lead and bromine enrichment in eclogite facies fluids extreme fractionation during lower crustal hydration hydration reactions associated with eclogite facies metamorphism of granulites in the norwegian caledonides led to the formation of saline brines with exceptional compositions primary omphacite and garnet hosted fluid inclusions from norwegian eclogites formed by hydration of granulites contain a plethora of solid phases a total of 18 different minerals have been identified in multiphase brines and 12 of these occur at the badsholmen locality in sunnfjord fluid inclusions from this locality are characterized by a high br cl mass ratio 0 03 and extreme pb enrichment as demonstrated by the presence of pb bearing daughter minerals including galena a pb cl bearing phase and a pb cl br bearing phase the fluid compositions may reflect enrichment of elements incompatible with the silicate structure during consumption of h 2 o by eclogite forming hydration reactions pb is believed to have been scavenged from the parent granulite by the increasingly saline brine during k feldspar breakdown

plume budgets in clear and cloudy convective boundary layers abstract from results of large eddy simulations of the clear convective boundary layer and of a stratus topped boundary layer mean properties of plumes that consist of updrafts and downdrafts are determined the plumes are defined locally by the sign of the vertical velocity or of moisture fluctuation or by a combination of both as a further alternative updraft and downdrafts in which the vertical velocity magnitude exceeds certain threshold values are considered the first two variants divide the motion field into two streams whereas in the other variants environmental air forms a separate stream the computed mean properties are in general agreement with existing measurements from the results we compute mean vertical fluxes assuming top hat profiles and compare these with the actual fluxes it is shown that the most uniform flux approximation is obtained if the plume structure is classified in terms of vertical velocity w for such w plumes the top hat profiles approximate about 60 of

structural mineralogical and petrophysical effects on deep crustal rocks of fluid limited polymetamorphism western gneiss region norway the proterozoic banded granulite facies complex of bardsholmen western gneiss region norway t 815 845 c was locally transformed to eclogite t 455 510 c p 12 kbar and amphibolite facies rocks t 460 c during the caledonian continental collision the granulite complex consists of mafic two pyroxene granulite and leucocratic orthopyroxene garnet bearing layers alternating on a scale from 1 cm to 10 m the granulite facies rocks change to eclogite facies rocks over centimetre scale distances along well defined fluid infiltration fronts the mafic granulite was transformed to omphacite garnet rich eclogites and the leucocratic rocks were converted to quartz phengite rich assemblages with minor garnet and local omphacite melange like lithologies consisting of mafic lenses of eclogite surrounded by felsic material represent an advanced stage in the process of converting deep crust to eclogite facies during amphibolitization this melange like lithology evolves to a rock where amphibolite lenses and layers are surrounded by granitoid gneiss a lithology typical of the western gneiss region the bardsholmen locality illustrates the profound control exerted by fluids on the timing of metamorphism the structural make up and petrophysical properties such as density and rheology of crustal root zones fluid induced metamorphism will therefore exert control on the attributes of orogenic belts such as topography and moho depth and influence the dynamics of collision zones by controlling the time of orogenic collapse and the buoyancy of the subducted crust we suggest that orogens may develop differently depending on the fluid budget

accelerated hydration of the earth s deep crust induced by stress perturbations the metamorphic cycle associated with the formation of mountain belts produces a lower crust containing little or no free fluid1 2 the introduction of external fluids to dry and impermeable volumes of the earth s crust is thus a prerequisite for the retrogressive metamorphism later observed in such regimes such metamorphism can cause significant changes in the crust s physical properties including its density rheology and elastic properties3 4 on a large scale the introduction of fluids requires the presence of high permeability channels such as faults or fractures which are the result of external tectonic stresses but extensive interaction between externally derived fluids and the fractured rock requires efficient mass transport away from the initial fractures into the rock itself and this transport often occurs over distances much longer than expected from grain boundary diffusion here we present both field observations and a simple network model that demonstrate how the transport of fluids into initially dry rock can be accelerated by perturbations in the local stress field caused by reactions with fluids we also show that the morphology of reaction fronts separating dry from wet rocks depends on the anisotropy of the external stress field

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

inferring marine atmospheric boundary layer properties from spectral characteristics of satellite borne sar imagery abstract for the commonly observed range of air sea temperature difference and surface wind speed the static stability of the atmospheric surface layer can have a significant effect on the mean surface stress and its turbulence scale horizontal variability while traditional satellite borne scatterometers have insufficient horizontal resolution to map this turbulence scale horizontal variability satellite borne synthetic aperture radars sar can this paper explores the potential for applying existing boundary layer similarity theories to these sar derived maps of turbulence scale horizontal variability in air sea stress two potential approaches for deriving boundary layer turbulence and stability statistics from sar backscatter imagery are considered the first approach employs monin obukhov similarity theory mixed layer similarity theory and a sar based estimate of the atmospheric boundary layer depth to relate the ratio of the mean and standard deviation of the sar derived wind speed field to the

a gabbro to eclogite transition on flemsoy sunnmore western norway the migmatitic gneisses on the nordoyane islands western norway enclose abundant inclusions of coronitic gabbros and different types of country rock eclogites gabbros on flemsoy show a prograde step wise transition to eclogite via a transitional stage in which garnet and orthopyroxene form coronas between igneous olivine and sodic plagioclase relics after igneous plagioclase cumulates eclogitization proceeds by a complex set of continuous and discontinuous reactions opx and spinel form as transient phases but are consumed in various omphacite forming reactions during eclogite recrystallization relict igneous clinopyroxene shows a continuous increase in jd content while garnet becomes less calcic and more homogeneous from the corona stage to recrystallized eclogite the reactions are strongly diffusion controlled and have been enhanced locally by oxidation and the presence of a fluid phase and deformation while low strain areas of the gabbros remained coronitic whole rock chemistry mineral parageneses and calculated p t conditions are similar for the gabbroeclogites and two types of country rock eclogites some of the layered country rock eclogites appear to have been derived from the coronite bodies p estimates are in the order 15 20 kbar while kgarcpxd values suggest maximum t values of 750 60 c for the eclogite metamorphism in the area

plumes in rotating convection part 1 ensemble statistics and dynamical balances atmospheric and oceanic convection often occurs over areas occupied by many localized circulation elements known as plumes the convective transports therefore may depend not only on the individual elements but also on the interactions between plumes and the turbulent environment created by other plumes however many attempts to understand these plumes focus on individual isolated elements and the behaviour of an ensemble is not understood geophysical convection may be influenced by rotation when the transit time of a convecting element is long compared to an inertial period for example in deep oceanic convection much recent attention has been given to the effect of rotation on individual plumes but the role of rotation in modifying the behaviour of an ensemble is not fully understood here we examine the behaviour of plumes within an ensemble both with and without rotation to identify the influence of rotation on ensemble plume dynamics we identify the coherent structures plumes present in numerical solutions of turbulent rayleigh benard convection a canonical example of a turbulent plume ensemble we use a conditional sampling compositing technique to extract the typical structure in both non rotating and rotating solutions the dynamical balances of these composite plumes are evaluated and compared with entraining plume models we find many differences between non rotating and rotating plumes in their transports of mass buoyancy and momentum as shown in previous studies the expansion of the turbulent plume by entrainment of exterior fluid is suppressed by strong rotation our most significant new result is quantification of the continuous mixing between the plume and ambient fluid which occurs at high rotation without any net changes in plume volume this mixing is generated by the plume plume interactions and acts to reduce the buoyancy anomaly of the plume by contrast in the non rotating case no such loss of buoyancy by mixing occurs as a result the total buoyancy transport by upwardly moving plumes diminishes across the layer in the rotating case while remaining approximately constant in the non rotating case at high values of rotation the net vertical acceleration is considerably reduced compared to the non rotating case due to loss of momentum through entrainment and mixing and a decelerating pressure gradient which partially balances the buoyancy driven acceleration of plumes as a result of the dilution of buoyancy the pressure gradient deceleration and the loss of momentum due to mixing with the environment in the rotating solutions the conversion of potential energy to kinetic energy is significantly less than that of non rotating plumes the combination of efficient lateral mixing and slow vertical movement by the plumes accounts for the unstable mean temperature gradient that occurs in rotating rayleigh benard convection while the less penetrative convection found at low rossby number is a consequence of the reduced kinetic energy transport within the ensemble of plumes identified by the conditional sampling algorithm distributions of vertical velocity buoyancy and vorticity mimic those of the volume as a whole plumes cover a small fraction of the total area yet account for most of the vertical heat flux

a second order bulk boundary layer model abstract bulk mass flux models represent the large eddies that are primarily responsible for the turbulent fluxes in the planetary boundary layer as convective circulations with an associated convective mass flux in order for such models to be useful it is necessary to determine the fractional area covered by rising motion in the convective circulations this fraction can be used as an estimate of the cloud amount under certain conditions matching conditions have been developed that relate the convective mass flux to the ventilation and entrainment mass fluxes these are based on conservation equations for the scalar means and variances in the entrainment and ventilation layers methods are presented to determine both the fractional area covered by rising motion and the convective mass flux the requirement of variance balance is used to relax the well mixed assumption the vertical structures of the mean state and the turbulent fluxes are determined analytically several aspects of this simple m

subduction and eduction of continental crust major mechanisms during continent continent collision and orogenic extensional collapse a model based on the south norwegian caledonides during continental collision in the middle silurian the thickness of the lithosphere under the caledonides of s norway was doubled by subduction of the western margin of baltica including the western gneiss region under laurentia crustal rocks of the baltic plate reached sub moho depths of near 100 km or more as inferred from the presence of coesite in eclogites isostatic calculations indicate an average elevation of the mountain chain of about 3 km at this stage the subducted lithosphere experienced vertical constrictional strains as a result of slab pull by its heavy and cold root eduction of the deeply buried crustal material was initiated by decoupling of the thermal boundary layer in the subducted lithosphere isostatic rebound resulted in very rapid uplift 1 2 mm yr 1 and the deep crust was exhumed mainly by tectonic extensional stripping over a period of 30 40 myr the eduction was probably related to a rolling hinge footwall uplift mechanism and the early high pressure coaxial fabrics were overprinted by extensional simple shear as the deep crust reached middle and upper crustal levels the model explains the present day normal crustal thickness under the exhumed deep rocks without necessarily invoking large scale lateral flow of material in the lower crust or igneous underplating

evolution of caledonian deformation fabrics under eclogite and amphibolite facies at vardalsneset western gneiss region norway the vardalsneset eclogite situated in the western gneiss region sw norway is a well preserved tectonite giving information about the deformation regimes active in the lower crust during crustal thickening and subsequent exhumation the eclogite constitutes layers and lenses variably retrograded to amphibolite and is composed of garnet and omphacite with varying amounts of barroisite actinolite clinozoisite kyanite quartz paragonite phengite and rutile the rocks record a five stage evolution connected to caledonian burial and subsequent exhumation 1 a prograde evolution through amphibolite facies t 490 63 c is inferred from garnet cores with amphibole inclusions and bell shaped mn profile 2 formation of l s tectonite eclogite t 680 20 c p 16 2 kbar related to the subduction of conti nental crust during the caledonian orogeny lack of asymmetrical fabrics and orientation of eclogite facies extensional veins indicate that the deformation regime during formation of the l s fabric was coaxial 3 formation of sub horizontal eclogite facies foliation in which the finite stretching direction had changed by approximately 90 disruption of eclogite lenses and layers between symmetric shear zones characterizes the dominantly coaxial deformation regime of stage 3 locally occurring mylonitic eclogites t 690 20 c p 15 1 5 kbar with top w kinematics may indicate however that non coaxial deformation was also active at eclogite facies conditions 4 development of a widespread regional amphibolite facies foliation t 564 44 c p 10 3 8 1 kbar quartz veins and development of conju gate shear zones indicate that coaxial vertical shortening and sub horizontal stretching were active during exhumation from eclogite to amphibolite facies conditions 5 amphibolite facies mylonites mainly formed under non coaxial top w movement are related to large scale movement on the extensional detachments active during the late orogenic extension of the caledonides the structural and metamorphic evolution of the vardalsneset eclogite and related areas support the exhumation model including an extensional detachment in the upper crust and overall coaxial deformation in the lower crust

progressive eclogitization under fluid present conditions of pre alpine mafic granulites in the austroalpine mt emilius klippe italian western alps metabasites from the austroalpine mt emilius klippe preserve different stages of the evolution from pre alpine granulite to alpine eclogite facies assemblages the pre alpine protolith includes layered garnet i clinopyroxene i plagioclase hornblende granulites and gabbros the eclogitic paragenesis comprises garnet ii clinopyroxene ii epidote ca amphibole chlorite eclogitic deformation is composite and involves two main episodes d1a d1b d1a produces a layer parallel foliation and incomplete transformation of granulites and is concluded by an episode of brittle deformation leading to the formation of eclogitic veins d1b gives rise to widespread s l tectonites and mylonites the eclogitic veins and surrounding haloes enriched in fluids during veining control the nucleation of d1b shear zones deformation is accomplished through ductile flow of reaction weakened plagioclase and hornblende sites and cataclasis of garnet i and clinopyroxene i both meso and microscale observations indicate that fluids play a primary role during eclogitization in both enhancing deformation and the kinetics of metamorphic reactions fluids influence plastic flow rates in matrix aggregates and promote fracturing of hard minerals the extent of metamorphic re equilibration is closely related to the density of the fluid pathways

structural development and petrofabrics of eclogite facies shear zones bergen arcs western norway implications for deep crustal deformational processes caledonian eclogite facies shear zones developed from grenvillian garnet granulite facies anorthosites and gabbros in the bergen arcs of western norway allow direct investigation of the relations between macroscopic structures and crystallographic preferred orientation cpo in lower continental crust field relations on the island of holsnoy show that the eclogites formed locally from granulite facies rocks by progressive development of 1 eclogite adjacent to fractures 2 eclogite in discrete shear zones 2 m thick 3 eclogite breccia consisting of 80 well foliated eclogite that wraps around rotated granulite blocks and 4 anastomosing subparallel eclogite facies shear zones 30 100 m thick continuous over distances 1 km within the granulite terrane these shear zones deformed under eclogite facies conditions at an estimated temperature of 670 50 c and a minimum pressure of 1460 mpa which corresponds to depths of 55 km in the continental crust detailed investigation of the major shear zones shows the development of a strong foliation defined by the shape preferred orientation of omphacite and by alternating segregations of omphacite garnet rich and kyanite zoisite rich layers a consistent lineation throughout the shear zones is defined by elongate aggregates of garnet and omphacite the cpo of omphacite determined from five axis universal stage measurements shows a strong b axis maximum normal to foliation and a c axis girdle within the foliation plane with weak maxima parallel to the lineation direction these patterns are consistent with deformation of omphacite by slip parallel to 001 and suggest glide along 010 the lineation and cpo data reveal a consistent sense of shear zone movement although the displacement was small localized faulting of high grade rocks accompanied by fluid infiltration can be an important mode of failure in the lower continental crust field relations show that granulite facies rocks can exist in a metastable state under eclogite facies conditions and imply that the lower crust can host differing metamorphic facies at the same depth deformation of granulite and partial conversion to eclogite such as is exposed on holsnoy island may be an orogenic scale process in the lowermost crust of collisional orogens

observations of the entrainment zone in a rapidly entraining boundary layer high rate turbulence data collected by the national center for atmospheric research electra aircraft on 13 january 1998 over lake michigan during the lake induced convection experiment are analyzed to explore the turbulence dynamics of the entrainment zone of a rapidly entraining convective boundary layer horizontal flight legs combined with the gentle slope of the lake enhanced boundary layer top yield high resolution profiles through the entrainment zone data analysis used a new maximally overlapping subleg reynolds decomposition algorithm to compute first second and third moment statistics for each flight leg then a compositing algorithm using 25 bins took like statistics from each flight leg and created smoothly varying curves that captured the variation of each statistic across the upper mixed layer and entrainment zone the analysis results reveal a conventional convective boundary layer below and a nonturbulent free atmosphere above a well resolved entrainment zone in the entrainment zone temperature and moisture skewness curves show that the last identifiable free atmosphere effects extend down well below the zero crossing of heat flux third moment statistics reveal considerable height dependence of the entrainment zone dynamics

localized polymorphic phase transformations in high pressure faults and applications to the physical mechanism of deep earthquakes earthquake mechanisms based on frictional instabilities are widely accepted for relatively shallow earthquakes such mechanisms in unmodified form are highly unlikely for deep earthquakes because of the expected high frictional shear stresses at depths of 300 700 km several alternative mechanisms have been proposed here i discuss a new type of shear instability observed in experiments on ordinary polycrystalline ice and polycrystalline tremolite by my colleagues and me these shear instabilities lead to rapid stress drops and sound emissions and have the following characteristics 1 a single sharp shear zone forms in the maximum shear stress orientation 2 confining pressure does not suppress the instability and under some conditions raising confining pressure pc lowers the differential stress at which it occurs 3 stress drops can occur repeatedly after reloading at about the same differential stress 4 the mean stress vs temperature conditions at which the instabilities occur in ice and tremolite place them in the fields of thermodynamic stability of ice ii and diopside talc respectively although i have not as yet confirmed the existence of these high pressure phases in the shear zones transformation in the shear zone is implicated because such shear instabilities do not occur in similar materials in which polymorphic phase changes do not occur reconstructive polymorphic phase changes localized along shear zones may be a general phenomenon in crystalline materials stressed non hydrostatically near transition boundaries moreover by analogy the reconstructive phase transformations that are thought to occur in deeply subducted lithosphere may lead to localized shear instabilities manifested by deep earthquakes and produce the observed double couple first motion distribution finally if this is the earthquake source mechanism in deeply subducted lithosphere then earthquakes should shut off when all of the polymorphic phase changes have occurred this may explain the maximum depth of earthquakes at about 680 km

prograde metamorphic zircon formation in gabbroic rocks the tale of microtextures u pb zircon dates of metagabbroic rocks such as eclogite mafic granulite and garnet amphibolite are used to constrain the timing of tectonometamorphic evolution in orogens worldwide for such interpretation however it is imperative to define at which stage of the p t evolution that zircon crystallization took place the prograde peak or retrograde stage in order to accurately interpret metamorphic zircon ages it is necessary to assess how the zircon crystallized or recrystallized as zircon can dissolve or grow under different metamorphic conditions zircon is robust to retrograde isotopic resetting under most crustal conditions but equilibrium zr mass balance models have suggested that zircon is largely produced during retrograde metamorphism this study takes a textural approach and identifies and reviews zircon forming textures and reactions in gabbro and metagabbro at different metamorphic grades ranging from subgreenschist to upper amphibolite and eclogite facies and at different stages of metamorphic recrystallization the textural relationships demonstrate that in metagabbro metamorphic zircon grows during the early stage of metamorphic recrystallization independent of pressure and temperature the mode of zircon formation is remarkably similar throughout different stages of metamorphic recrystallization and the most significant source of zr is igneous baddeleyite hence in contrast to the equilibrium mass balance model most zircon in metagabbro forms by prograde metamorphic reactions that consume igneous phases and not by late retrograde reactions and the onset of zircon forming reactions is governed primarily by the introduction of a hydrous fluid commonly accompanied by ductile deformation less

experimental modelling of corona textures formation of corona textures along olivine plagioclase and orthopyroxene plagioclase interfaces has been experimentally reproduced at 670 and 700 c and 5 kbar with either a pure h2o fluid phase or 0 1 and 37 m nacl h2o solution fluid in these experiments we investigate the interaction of primary olivine and or orthopyroxene and plagioclase in powders and polished crystals and in small samples of a natural gabbro the experiments result in the formation of corona textures with several layers of different assemblages according to the experimental conditions consisting of garnet grossular clinopyroxene orthopyroxene amphibole chlorite and phlogopite the experiments show major differences in the number of layers the mineral assemblages and mineral composition and in the trends of composition of plagioclase in coronas around olivine and orthopyroxene the fluid phase composition influences the corona assemblages and the composition of the minerals in the experimental coronas for example garnet appears in the coronas in the second experiment where the nacl h2o ratio is low experimental modelling of corona textures confirms a model of simultaneous growth of layers by the mechanism of diffusion metasomatism with participation of a fluid phase through which mass is transferred zoning in the experimental coronas shows opposing diffusion of al and ca from plagioclase and mg and fe from olivine orthopyroxene difference in the mobility of the components is inferred from observations in the coronas the experimental corona textures are compared with natural coronas from the belomorian belt baltic shield developed at 670 690 c and 7 8 kbar and the marun keu complex polar urals developed at 670 700 c and 14 16 kbar where the corona textures correspond to a transitional stage of the gabbro to eclogite transformation

coesite in clinopyroxene in the caledonides and its implications for geodynamics coesite is reported for the first time from the caledonide orogen it occurs as inclusions in clinopyroxene in the dolomite eclogite at grytting norway and provides valuable new evidence to support the hypothesis of extremely high pressure 30 kbar in certain norwegian eclogites this finding has implications for the geodynamics and kinetics of the concepts of microscale intracrystalline tectonic overpressure and of macroscale local or regional tectonic overpressure and for the hypotheses of subduction and obduction involving a more than 100km vertical component of transport

long term observations of the convective boundary layer using insect radar returns at the sgp arm climate research facility abstract a long term study of the turbulent structure of the convective boundary layer cbl at the u s department of energy atmospheric radiation measurement program arm southern great plains sgp climate research facility is presented doppler velocity measurements from insects occupying the lowest 2 km of the boundary layer during summer months are used to map the vertical velocity component in the cbl the observations cover four summer periods 2004 08 and are classified into cloudy and clear boundary layer conditions profiles of vertical velocity variance skewness and mass flux are estimated to study the daytime evolution of the convective boundary layer during these conditions a conditional sampling method is applied to the original doppler velocity dataset to extract coherent vertical velocity structures and to examine plume dimension and contribution to the turbulent transport overall the derived turbulent statistics are consistent with previous aircraft and lidar observations the obs

continental eclogites and the wilson cycle the wilson cycle the repeated opening and closing of oceans commonly along roughly the same lines is here attributed to the presence of eclogite facies roots of partially collapsed orogens we present a finite element thermal model that suggests that such roots will weaken the orogenic lithosphere relative to that of the adjacent foreland for hundreds of millions of years and make it a preferred site for later rifting

microdiamond in high grade metamorphic rocks of the western gneiss region norway three grains of microdiamond were recovered from high grade gneiss exposed in the western gneiss region norway identification and characterization of the diamond grains by raman and infrared spectroscopy indicate the presence of substitutional impurities of h and n primary fluid inclusions in garnet and quartz in the diamond bearing rock demonstrate the evolution of metamorphic volatile fluids from reduced n 2 co 2 compositions during the peak phase of metamorphism to n 2 ch 4 h 2 o bearing compositions during retrograde metamorphism compatible geologic petrologic and fluid composition data imply a metamorphic origin for the microdiamonds if so the metamorphic and fluid conditions recorded by the microdiamonds and gneissic host may be applicable to microdiamond investigations in other high pressure regionally metamorphosed orogens

zircon geochemical constraints on the protolith nature and metasomatic process of the mg rich whiteschist from the western alps abstract the mg rich silicic crustal rocks characterized by high sio2 and mgo contents are widespread in the alps providing rare targets to investigate the origin of mg rich fluids in the continental subduction zone however it is a prerequisite to elucidate the protolith nature of such mg rich rocks including the possible alteration process experienced before the alpine metamorphism for this purpose we carried out a detailed study of trace elements o hf isotopes and u pb ages for zircons from the coesite bearing whiteschist and its country rock metagranite at dora maria in western alps the whiteschist is characterized by much higher mgo contents than the adjacent metagranite relict magmatic zircons from the two types of rocks give essentially the same u pb ages of 262 ma similar ree contents and patterns the same range of ehf t1 values from 6 4 to 2 8 and 18o values from mostly 9 to 11 these features provide compelling evidence that the whiteschist and metagranite share the same protolith i e the permian granite all the above geochemical compositions are consistent with the argument that the high mgo content of the whiteschist was acquired from high mg fluids from dehydration of the serpentinized peridotite at the slab mantle interface in the continental subduction channel the hypothesis of a pre alpine hydrothermal alteration of the granitic protolith to cause the mgo enrichment is not favorable zircon in the metagranite does not show any metamorphic overgrowth during the alpine orogeny in contrast to the extensive overgrowth of metamorphic rims at 35 ma in the whiteschist the metamorphic rims show relatively low ree contents with variably flattened hree patterns different from the relict magmatic zircons that exhibit relative high ree contents with steep hree patterns this difference suggests that the breakdown of hydrous minerals plays a crucial role in dictating mineral reactions for zircon growth during the continental subduction zone metamorphism this interpretation is also consistent with the local occurrence of garnet coronae along the grain margins of biotite in the metagranite therefore this study provides not only the constraints on the protolith nature and metasomatic process of mg rich whiteschist from the western alps but also insights into the role of metamorphic fluids in controlling mineral reactions for the metamorphic growth of both zircon and garnet in the continental subduction zone

metasomatism of gabbro mineral replacement and element mobilization during the sveconorwegian metamorphic event widespread metasomatism affected the 100 km long and 25 km wide proterozoic bamble and modum kongsberg sectors south norway resulting in the chemical and mineralogical transformation of wide segments of continental crust scapolitization was associated with veining and was followed by albitization transforming metagabbros pervasively over large areas fluids played an active role in these reactions forming h2o co2 and cl bearing phases at the expense of the primary volatile free minerals causing depletion in fe and infiltration of k mg na b and p the transformation of gabbro to scapolite metagabbro is observed as a fluid front replacing the primary magmatic mineral assemblage in three stages during an incipient amphibolitization stage the primary mafic minerals were replaced by anthophyllite or hastingsite followed by pargasitic and edenitic ca amphibole magnetite was dissolved while rutile formed by the breakdown of ilmenite plagioclase was replaced by cl rich scapolite me19 42 reflecting cl saturation while k and mg saturation produced phlogopite enstatite sapphirine and rare corundum the high modal contents of chlorapatite and tourmaline in the scapolite metagabbro imply infiltration of b and p the albitites consist dominantly of albite ab95 98 with varying generally small amounts of chlorite calcite rutile epidote and pumpellyite they formed from a h2o co2 fluid rich in na the gabbro yields a zircon u pb age of 1149 7 ma and tonalite 1294 38 ma whereas rutile from scapolite metagabbro and albitite has u pb ages of 1090 1084 ma and phlogopite produced during scapolitization rb sr ages of 1070 1040 ma temperature conditions for the scapolitization are inferred to have been 600 700 c the reported ages combined with mineralogical and petrographic observations and inferred p t conditions indicate that the metasomatism was a part of the regional sveconorwegian amphibolite facies metamorphic phase initial 87sr 86sr of the scapolite ranges from 0 704 to 0 709 the sr signature the cl and b rich environment and regional distribution of lithologies suggest that the fluid may have originated from evaporites that were mobilized during the regional metamorphism

interaction between fluid flow fracturing and mineral growth during eclogitization an example from the sunnfjord area western gneiss region norway in sunnfjord western gneiss region of south norway a proterozoic layered gabbro complex displays various degrees of transformation to eclogite in the unreacted parts layering in the gabbro is defined by modal variations of plagioclase olivine pyroxenes and minor fe ti oxide and spinel coronitic and foliated eclogite formed from the gabbro by hydration reactions at t 510 620 c causing a volume decrease of c 13 in the coronitic eclogite the mafic magmatic phases are replaced by aggregates of omphacite barroisite tremolite talc and rutile whereas the plagioclase domains are pseudomorphed by omphacite barroisite clinozoisite kyanite paragonite and garnet the felsic and mafic domains are separated by a garnet rim up to 5 mm thick garnet was also formed along dilational veins connecting and radiating out of coronas including the same eclogite facies minerals in addition microfractures filled by amphibole and omphacite cut through the corona and vein garnet oriented perpendicular to the garnet layering the transformation of dry gabbro to eclogite with hydrous minerals requires supply of water the timing of metamorphic reactions is therefore dependent on the timing of fluid introduction the inclusion pattern of garnet in the holt tyssedalsvatnet metagabbro complex indicates that transformation started under eclogite facies conditions brittle deformation in form of fractures allowing infiltration of fluids and mobilisation of elements is shown to be the most important process initiating transformation brittle deformation is thereby active in deep crustal levels corresponding to eclogite facies conditions fracturing is interpreted as having been caused by a combination of high fluid pressure volume changes during mineral transformations and external stresses ductile deformation started after the initial metamorphic transformation garnet chemistry and zoning pattern are controlled by the chemistry of the growth place the fluid influx and element supply abrupt chemical variations across corona garnet may have been formed by an interaction between rapid growth and transport along microfractures between plagioclase and mafic domain the metamorphic transition proceeded rapidly the transformation of the deep crust to eclogite can be viewed as a dynamic process where the volume changes result in fracturing and these fractures funnelling fluid and element enhancing mineral reaction the densification causes further fracturing indicating that the process is self driven provided that fluid is available

flow variability in the scandinavian ice sheet modelling the coupling between ice sheet flow and hydrology abstract there is increasing geologic evidence for periodic flow variability within large ice sheets manifested as spatially and temporally variable areas of fast ice flow and resulting in the very complex patterns of lineations observed in formerly glaciated areas however many ice sheet models do not replicate this behaviour a possible reason for this is that such models do not include a detailed treatment of basal hydrology changes in the character of sub glacial drainage systems are believed to cause surges in valley glaciers recent ice sheet models which have included basal hydrology or at least a link between basal velocity and the presence of water at the bed often show flow variability however these models have typically assumed a deformable bed or have made no assumptions about the nature of the bed whilst these assumptions seem applicable to areas close to the former margins of quaternary ice sheets they are less applicable to interior areas these areas typically show thin or scanty till cover over eroded bedrock and the presence of eskers which are indicative of drainage in sub glacial tunnels we have developed a two dimensional time dependent ice sheet model that includes hard bed basal hydrology this allows calculation of sub glacial water pressures and the use of a water pressure dependent sliding law to calculate ice sheet velocities when used to simulate the weichselian scandinavian ice sheet with late quaternary climate and sea level as forcing functions this model develops localised areas of fast flowing ice which vary in extent and in distance of penetration into the interior of the ice sheet both spatially and temporally the behaviour of these lobes depends crucially on the influence of the evolving ice sheet topography on the routing of subglacial water flow due to the resulting variations in the subglacial hydraulic potential which drive the water flow bedrock topography also has some influence but fast flow areas are not confined to obvious topographic troughs a relatively thin ice sheet with low surface slopes is produced in areas experiencing fast ice flow generally two to four separate areas of fast flow can be recognised and these are similar in size and shape to the lobes identified in some geologically based reconstructions of the scandinavian ice sheet within the fast flowing areas sub glacial drainage is typically in a cavity based system however tunnel based drainage is predicted to have extended up to 150 km from the ice sheet margin particularly during deglaciation because of the changes in ice sheet topography associated with fast flow and the resulting changes in the pattern of sub glacial water flow the model predicts that these fast flowing lobes interacted in complex ways and exhibited quasi periodic switching between fast and slow flow

the significance of grain scale stresses in the kinetics of metamorphism during metamorphism phases grow and dissolve dominantly along grain boundaries bulk diffusion models for the development of metamorphic textures often assume that diffusion is homogeneous in regions of each phase rather than being localised along phase boundaries under isotropic stress chemical potentials of components involved in reactions are likely to be buffered along grain boundaries between phases thus inhibiting diffusion and growth motive forces must exist which overcome this and it is proposed here that local heterogeneous stresses will be important a mathematical theory for stress controlled growth is derived this theory predicts that the growth rates of two phases along their mutual interface will be linked in a quantifiable way it forms a basis for considering the important effects of stresses induced by local volumetric changes during metamorphism and it provides a link between these effects and those related to pressure solution in deforming rocks

rheology of the plate interface dissolution precipitation creep in high pressure metamorphic rocks abstract subduction zone models invoke deformation to be concentrated along the plate interface in a region of particularly low temperature geophysical observations do not provide constraints on temperature stress and deformation patterns with desired resolution in contrast the record of high pressure metamorphic rocks exhumed from subduction zones provides details on p t history deformation mechanisms and stress state albeit not readily correlated with the former dynamic situation on larger scale here we review available information on dissolution precipitation creep dpc in high pressure metamorphic rocks which if representative for subduction zones in general can pose constraints on conditions rheology and flow patterns along the plate interface the key observations and conclusions are that 1 deformation is typically highly inhomogeneous and localized into shear zones 2 stresses are generally too low to drive crystal plastic deformation 3 microfabrics suggest dissolution precipitation creep to be the predominant deformation mechanism 4 an aqueous fluid at quasi lithostatic pressure is available throughout allowing for tensile fracturing and crack healing or sealing 5 low stress combined with high strain rates required for localized deformation at typical subduction rates implies low viscosity and 6 contribution of shear heating to the thermal budget of subduction zones should be moderate the dominant deformation mechanism dpc is reviewed in some detail including experimental and theoretical approaches various examples of dpc in high pressure metamorphic rocks are illustrated emphasizing the role of interphase boundaries as sites of dissolution rheology governed by dpc is proposed to control interplate coupling and development of a subduction channel with return flow being a likely candidate for rapid exhumation of high pressure metamorphic rocks

geochronology of high pressure mafic granulite dykes in sw sweden tracking the p t t path of metamorphism using hf isotopes in zircon and baddeleyite although the u pb zircon chronometer has been widely used for dating metamorphism in moderate to high grade rocks it is generally difficult to link the u pb age of zircon to specific metamorphic reactions in this study the initial hf isotopic composition of secondary zircon is compared with the evolution of hf isotopic composition of the bulk sample back projected from the measured value through time this approach may enhance the interpretation of radiometric ages performed on metamorphic mineral assemblages here u pb sm nd and lu hf geochronology and thermobarometry have been integrated and applied to two metamorphosed diabase dykes in the sveconorwegian orogen sw sweden the dykes are located 5 km east of the nne trending gota alv deformation zone in the idefjorden terrane and trend parallel to this zone the lunden dyke is recrystallized into a coronitic granulite facies assemblage u pb isotopic analyses of baddeleyite in this dyke indicate an emplacement age of 1300 ma thermobarometric techniques applied to garnet and omphacitic clinopyroxene coronas indicate high pressure metamorphism at c 15 kbar and c 740 c growth of polycrystalline zircon at the expense of baddeleyite occurred at 1046 6 ma identical hf isotopic composition of polycrystalline zircon and baddeleyite shows that the baddeleyite to zircon transition took place before hf equilibration among the other metamorphic minerals and hence the c 1046 ma age of polycrystalline zircon sets an upper age limit of metamorphism of this sample the haregarden dyke is recrystallized into a granoblastic transitional upper amphibolite to granulite facies assemblage the estimated p t conditions are c 10 kbar and c 700 c analyses of small 30 m clear and round zircon in this sample yield a concordia u pb age of 1026 4 ma which is indistinguishable from the lu hf and sm nd mineral isochron ages of 1027 9 ma and 1022 34 ma this type of secondary zircon plots at the lower end of the lu hf isochron and indicates simultaneous growth with garnet at c 1026 ma a time when hf isotopic equilibrium among minerals must have been reached

incomplete high p t metamorphic transitions within the kvamsoy pyroxenite complex west norway a case study of disequilibrium the kvamsoy pyroxenite complex consists of olivine websterite olivine gabbro and leucogabbro norite which have been subjected to regional high p t hpt metamorphism the metamorphism has resulted in a range of disequilibrium textures with the development of coronas and pseudomorphism of the igneous phases reactions between felsic and mafic mineral domains have been controlled by variable and selective diffusion of elements resulting in a variety of local plagioclase breakdown reactions and in significant compositional variations for the product garnet restricted diffusion favours transient reaction stages with garnet spinel corundum zoisite after calcic plagioclase in olivine gabbro and olivine websterite and garnet spinel kyanite quartz sodic plagioclase in leucogabbro norite complete hpt reaction has produced garnet pyroxenite which consists of garnet diopside hornblende zoisite in gabbroic rocks while amphibolitization continued during the cooling and uplift history grt ky pl qtz geobarometry suggests pressures in the range 13 16 kbar for t 750 c comparable with the regional eclogite forming metamorphism

a multiple mass flux parameterization for the surface generated convection part i dry plumes abstract the present study introduces a parameterization for the mixing in the surface generated free convection regime including dry and moist convection cases the parameterization explicitly represents the plumes that drive the convective turbulence ascending parcels that have similar properties in the surface layer are grouped into updrafts with a determined fractional area the updrafts ascend according to an entraining plume model and may eventually overturn the plume model can either use a time or a length scale for the lateral entrainment closure the plumes environment is assumed to be horizontally uniform a one dimensional framework is used to evaluate the parameterization in the case of a dry convective boundary layer cbl the predicted variances are underestimated presumably due to the uniform environment assumption the contrast between the strong upward motions and the compensating subsidence is simulated and the skewness of w increases realistically with height the plumes dyn

processing of crust in the root of the caledonian continental collision zone the role of eclogitization segments of the root to the caledonian collision zone are exposed along the west coast of norway allowing the study of processes and petrophysical conditions at the deepest crustal levels p t conditions prevailing in these crustal root zones correspond to eclogite facies eclogitization is associated with marked changes in petrophysical properties notably a density 10 15 and vp increase which may give a mantle signature to an eclogitized crust the observed ductility enhancement may be caused by transformation plasticity reduction in grain size formation of new mineral assemblages and presence of fluid in the western gneiss region and the bergen arcs eclogites form along shear zones interpreted as fluid pathways with sharp boundaries to their metastable protolith this makes eclogite shear zones potential deep crustal reflectors dry crust subducted into roots of continental collision zones will undergo eclogitization only if hydrous fluids are available timing of metamorphic reactions does not depend on crossing of equilibrium boundaries in the p t space but rather on the introduction of fluids into the system eclogites are not only passive recorders of p t t paths illustrating very deep subduction of crust 100 km rapid changes in petrophysical properties make fluid induced eclogitization a dynamic process that influences geodynamics stresses set up by the volume changes or by tectonic forces are released by ductile deformation along shear zones and by seismic faulting as evidenced by syn eclogitic pseudotachylytes in the metastable protolith deformation including seismicity enhances fluid infiltration and further eclogitization dense and rheologically weak eclogites may delaminate and sink into the mantle in the absence of fluids crustal doubling may occur without metamorphic re equilibration the evolution of a collision zone depends on the fluid regime which should be considered in geodynamic modelling in addition to p and t

complex growth textures in a polymetamorphic metabasite from the kraubath massif eastern alps zoned garnet and amphibole occur in metabasites of the kraubath massif eastern alps that contain relic magmatic clinopyroxene the amphibole composition gradually changes from core xmg 1 4 0 83 to rim xmg 1 4 0 6 0 7 a number of compositional varieties of garnet occur in the metabasite an older porphyroblastic garnet py23 27 alm41 43 grs29 33 has two different compositional domains one relatively rich in mg py27 30 and the other rich in ca grs35 38 with a low mg py20 25 content the youngest variety which forms rims on or microveins in the porphyroblastic garnet has high ca and low mg grs40 57 py2 7 alm46 51 the amphibole cores and garnet porphyroblasts are interpreted to represent minerals formed during variscan regional metamorphism under amphibolite facies conditions alpine metamorphism is represented by the most recent ca rich and mg poor variety of garnet that coexists with the amphibole rims epidote and chlorite fracturing in the porphyroblastic garnet probably originated during retrogression of the variscan amphibolite facies assemblages textural relations suggest that the garnet in the microveins formed by dehydration of hydrous phases during an alpine metamorphic overprint that reached p t conditions of 550 583 c at 1 0 gpa

the complex hydrothermal history of granitic rocks multiple feldspar replacement reactions under subsolidus conditions recurring subsolidus re equilibration of granitic feldspars induced by fluid infiltration events provides a record of fluid rock interactions that affect large volumes of the earth s continental crust this has a direct bearing on the interpretation of the present day granitic rock mineralogy and geochemistry we examine palaeoproterozoic grey and red stained granitoids from the simpevarp and laxemar areas in se sweden particularly focusing on consecutive feldspar replacement reactions to provide an in depth understanding of subsolidus re equilibration of granitic rocks with hydrothermal fluids the apparently most unaltered grey granitoids contain highly porous oligoclase grains that enclose crystallographically continuous microcline relicts this texture suggests that the oligoclase is already secondary and may be a replacement product of original microcline oligoclase is progressively replaced by albite an9 along polysynthetic twinning and intragranular fractures the features of this replacement are characteristic of a dissolution reprecipitation mechanism finegrained mica sericite is closely associated with the albite porosity within micron sized pores observable with scanning electron microscopy as well as in nanopores imaged with transmission electron microscopy the reddening phenomenon in the vicinity of fractures is contemporaneously related to the k feldspathization of sericite which is restricted to the altered oligoclase submicron size hematite precipitation within orthoclase pores at the replacement front results in the red coloration the complex associations between the fluid feldspar reactions indicate that the replacement reactions may be due to sequential fluid infiltration events and that the granitoids have undergone extensive subsolidus re equilibration changing the original magmatic mineralogy therefore the effects of large scale re equilibrations of granitic rocks through hydrothermal convection systems should be more closely considered

a combined eddy diffusivity mass flux approach for the convective boundary layer a better conceptual understanding and more realistic parameterizations of convective boundary layers in climate and weather prediction models have been major challenges in meteorological research in particular parameterizations of the dry convective boundary layer in spite of the absence of water phase changes and its consequent simplicity as compared to moist convection typically suffer from problems in attempting to represent realistically the boundary layer growth and what is often referred to as countergradient fluxes the eddy diffusivity ed approach has been relatively successful in representing some characteristics of neutral boundary layers and surface layers in general the mass flux mf approach on the other hand has been used for the parameterization of shallow and deep moist convection in this paper a new approach that relies on a combination of the ed and mf parameterizations edmf is proposed for the dry convective boundary layer it is shown that the edmf approach follows naturally from a decomposition of the turbulent fluxes into 1 a part that includes strong organized updrafts and 2 a remaining turbulent field at the basis of the edmf approach is the concept that nonlocal subgrid transport due to the strong updrafts is taken into account by the mf approach while the remaining transport is taken into account by an ed closure large eddy simulation les results of the dry convective boundary layer are used to support the theoretical framework of this new approach and to determine the parameters of the edmf model the performance of the new formulation is evaluated against les results and it is shown that the edmf closure is able to reproduce the main properties of dry convective boundary layers in a realistic manner furthermore it will be shown that this approach has strong advantages over the more traditional countergradient approach especially in the entrainment layer as a result this edmf approach opens the way to parameterize the clear and cumulus topped boundary layer in a simple and unified way

metamorphic evolution of norwegian country rock eclogites as deduced from mineral inclusions and compositional zoning in garnets abstract detailed studies of pre early syn and post eclogite mineral associations in some west norwegian country rock eclogites have made it possible to reconstruct their metamorphic evolution pre eclogite stages are represented by various amphibolite facies associations found in the central parts of prograde zoned garnets early and syn eclogite stages are represented by various eclogitic assemblages containing low and high jd omphacites respectively the former located in the intermediate zones and the latter in the outermost rims of prograde zoned garnets and in the matrix post eclogite stages include granulite amphibolite and greenschist facies associations representing replacement phases after higher grade assemblages p t estimates indicate a prograde evolution along an extremely steep p t gradient 7 9 kbar over 100 200 c while the initial post eclogite evolution involved a nearly adiabatic decompression on the order of 10 kbar

the tectonic implications of solundian upper devonian magnetization of the devonian rocks of kvamshesten western norway the allochthonous old red sandstone of kvamshesten western norway records polyphase orogenic deformation and palaeomagnetic results from both the devonian sediments and mylonites associated with the basal thrust define a syn to post tectonic magnetization withd 218 i 3 and 95 9 7 the corresponding pole position lat 21 s long 324 e suggests a late devonian early carboniferous magnetization age solundian and probably dates the time of thrust movements

uranium lead zircon and titanite ages from the northern portion of the western gneiss region south central norway abstract the geochronologic history of the northern portion of the western gneiss region south central norway has been investigated by u pb analyses of zircon and titanite from various basement units and one supracrustal gneiss a six point four zircon and two titanite discordia line from a migmatite melt pod and its host gneiss astfjord migmatite gneiss defines upper and lower intercept ages of 1659 1 1 8 ma and 393 6 3 6 ma respectively the upper intercept age is interpreted as a time of tonalite emplacement and migmatite formation in the region a seven point three zircon and four titanite discordia line from the ingdal granite gneiss has similar upper and lower intercept ages 1652 9 1 7 ma and 396 1 4 9 ma respectively and the upper intercept age is interpreted as the time of granite crystallization the lower intercept age from both theastfjord migmatite gneiss and the ingdal granite gneiss is interpreted as the time of regional metamorphic resetting and is evidence for caledonian influence in the region titanite from these two gneiss units as well as from other tonalite granite and supracrustal gneisses throughout the western gneiss region displays a remarkably uniform pattern of discordance titanite discordance is variable from 6 to 100 and in general the degree of discordance is proportional to the caledonian metamorphic grade of nearby supracrustal schists episodic diffusional lead loss from titanite during caledonian metamorphism probably caused the discordance pattern but a combined mechanism of mixing and diffusional lead loss cannot be ruled out in any case the seventeen point titanite and zircon discordia line clearly indicates that 1 the bulk of the granitoid terrane in this portion of the western gneiss region was emplaced migmatized and cooled in a short time interval about 1657 ma ago 2 a second short lived thermal event that exceeded the blocking temperature of titanite occurred about 395 ma ago and 3 titanite and zircon in the region were not isotopically disturbed by comparable geologic events in the period from 1657 to 395 ma or at any time after 395 ma

eclogite facies polyphase deformation of the drosdal eclogite western gneiss complex norway and implications for exhumation abstract exhumation of the deep crust during orogenic extension is accepted as a geological phenomenon but structures formed during burial and the earliest stages of exhumation are often overprinted by deformation events occurring at shallower crustal levels the western gneiss complex wgc of norway comprises variably retrogressed high pressure hp and ultrahigh pressure uhp eclogite bodies enclosed in predominantly felsic amphibolite facies rocks the drosdal body located in the sunnfjord area is one of the largest and best preserved eclogites in the wgc and comprises over ca 3 km2 of exposed eclogite facies rocks it is an excellent example of an eclogite tectonite and displays a wealth of structures formed during deformation at a minimum depth of 50 km and peak temperatures of ca 800 c large volumes of mylonites with the eclogite facies assemblage garnet clinopyroxene quartz amphibole clinozoisite phengite kyanite rutile are preserved structures associated with the eclogite facies metamorphism include e w trending isoclinal folds boudinage hinge parallel lineations and meter scale kyanite dominated veins the drosdal body was tightly folded on the kilometer scale under eclogite facies conditions subsequently the shapes of the drosdal body and other mafic bodies in the sunnfjord area were modified during eclogite to amphibolite facies e w directed stretching to give boudin like lenses the timing of formation of a pervasive eclogite facies lineation eclogite facies folds and kyanite bearing veins overlapped substantially and this portion of the deformation history was dominated by a constrictional strain field partitioning of deformation occurred after a substantial amount of eclogite facies deformation had already taken place and resulted in the relative rotation of linear features in specific zones on the scale of 400 m the eclogite facies lineations and fold hinges within the drosdal body are subparallel to amphibolite and greenschist facies structures throughout the wgc although circumstantial this suggests that structures belonging to each of these three metamorphic facies formed during one progressive deformation event corresponding to extensional exhumation our observations are consistent with models involving inhomogeneous deformation of the lower crust during early orogenic extension we envisage that transtensional noncoaxial deformation dominated the extensional deformation of the wgc but that coaxial deformation must have occurred locally

coherent structures in large eddy simulations of a nonprecipitating stratocumulus topped boundary layer abstractthe properties of coherent convective structures are analyzed in a nonprecipitating marine nocturnal stratocumulus topped boundary layer stbl with a series of high resolution large eddy simulations less a new classification method based on octant analysis using vertical velocity and two passive scalars is introduced to systematically define convective structures in both the cloudy and the cloud free regions it is therefore possible to detect and track updrafts downdrafts and their turbulent shells both ascending and subsiding together with the entraining air from the inversion layer or the free troposphere the geometrical and thermodynamical characteristics e g areal fraction temperature liquid and total water mixing ratio buoyancy of those structures are then accurately described and particular attention is given to their respective contributions to the turbulent transport of mass heat and moisture it is shown that updrafts downdrafts and entrainment are equally important

eclogite formation and dynamics of crustal roots under continental collision zones field observations on deep parts of the root zone of the caledonian orogen are combined with the geophysical data available for recent continental collision zones such as the alps to provide a model for dynamics of crustal root zones rocks descending into the root zone are locally infiltrated by fluids which cause eclogitization along shear zones and fluid pathways the eclogite facies rocks vary in density from 3 1 to 3 6 g cm 3 reflecting the compositional variation in their protoliths where the amount of highly ductile eclogitic material reaches about 40 the descending crustal segment loses its coherence and disintegrates into a breccia where blocks of granulite facies rocks float in a matrix of eclogite material a density stratified root zone develops where light unreacted or partly eclogitized material floats on an ocean dominated by eclogite facies rocks the top of which may correspond to the moho catastrophic decent of this eclogitic layer may 1 transport blocks of light material to depths of 90 km which upon further disintegration due to eclogitization are released and return by buoyancy forces to the crust 2 result in extension and uplift of the partly eclogitized lighter material

distribution of hydrous components in jadeite of the dabie mountains two kinds of jadeite occur in the jadeite quartzite from the dabie mountains eastern china associated either with weak or strong deformation the former shows a uniform composition while the latter shows both uniform and zoning composition these jadeites were examined with infrared ir spectroscopy all jadeite displays hydroxyl oh stretching bands implying that hydrous components commonly exist in jadeite the concentration of the hydrous components in the jadeite with weak deformation is homogenous whereas the concentration of the hydrous components in strongly deformed samples is variable the correlation between the intensity of oh band absorbance and compositional zoning of jadeite with strong deformation indicates that na rich jadeite can accommodate more oh than na poor jadeite its interpretation is that there is more na associated with greater oh availability in the initial crystallization environment our data of the comparatively high oh concentrations recorded in the core of the jadeite which contains relative high vacancies in m2 site imply that both oh content and the vacancies in m2 site could decrease during exhumation of the jadeite quartzite the decrease of oh solubility in jadeite would result in the formation of h2o fluid during the early exhumation of uhp metamorphic rocks the h2o fluid transformed from oh during exhumation could trigger and enhance the early retrograde metamorphism of the host rocks and facilitate plastic deformation of jadeite grain by dislocation creep and diffusion creep

rates of grain boundary diffusion through enstatite and forsterite reaction rims the growth rates of enstatite rims produced by reaction of fo92 and sio2 were determined at 250 1500 mpa and 900 1100 c for a wide range of water contents growth rates were also determined for forsterite rims between mgo and mg2si2o6 and between mgo and sio2 rim growth rates are parabolic indicating diffusion controlled growth of the polycrystalline rims which are composed of 2 m diameter grains rim growth rates were used to calculate the product of the grain boundary diffusion coefficient d a times the effective grain boundary thickness assuming in turn that mgo sio2 and mg2si 1 are the diffusing components coupled diffusion of a cation and oxygen or interdiffusion of mg and si the values for d mgo d and d for enstatite at 1000 c and 700 mpa confining pressure with about 0 1 wt water are about five times larger than the corresponding d a values for samples initially vacuum dried at 250 c most of the increase in d a occurs with the first 0 1 wt water the activation energy for diffusion through the enstatite rims 1100 950 c is 162 30 kj mole the diffusion rate through enstatite rims is essentially unchanged for confining pressures from 210 1400 mpa but the nucleation rate is greatly reduced at low confining pressure for 1 0 wt water present and limits the conditions at which rim growth can be measured the corresponding values for d a through forsterite rims are essentially identical for the two forsterite producing reactions when 0 1 wt water is added and similar to the d a values for enstatite at the same conditions the d a values for forsterite are 28 times larger for samples starting with 0 1 wt water compared to samples that were first vacuum dried thus water enhances these grain boundary diffusion rates by a factor of 5 30 depending on the mineralogy but the total range in d a is only slightly more than an order of magnitude for as wide a range of water contents as expected for most crustal conditions

micro scale element migration during eclogitisation in the bergen arcs norway a case study on the role of fluids and deformation abstract understanding chemical element mobility during high pressure metamorphism is paramount to the knowledge of the transformations occurring during the course of eclogite facies metamorphism in particular the role of deformation and fluid circulation appear essential in order to better decipher this role we investigated two eclogite facies samples from the lindas nappe in the bergen arcs norwegian caledonides which are related to a fluid deformation metamorphic event this study based on detailed microtextural investigations coupled with major and trace element analyses either in situ empa and la icp ms or by conventional icp ms nebulisation on mineral fractions illustrates the complexity of chemical reactions accompanying the eclogite and amphibolite facies metamorphism a single eclogite facies mineral species two eclogite facies i e phengite and epidote depicts various chemical features depending on its textural location at thin section scale the correlation with the mineralogical reaction occurring in each textural site demonstrates that the compositional variations are inherited from the precursor minerals thus the composition of eclogite facies minerals is locally controlled by the composition of few hundred micron domains on the contrary alteration phases of the amphibolite facies symplectite and calcic amphibole display clear enrichment in lile pb sr and lree compared to their precursor minerals omphacite and garnet this supports that the transport of elements at hand sample scale was enhanced during the retrogression and elements were efficiently delocalised from one textural site to another the contrasting behaviour of element mobility between peak eclogite facies metamorphism and retrogression can be explained in terms of rate processes and fluid deformation activity during eclogitisation deformation allows the formation of textural and mineralogical microdomains contemporaneously the fluid circulation favours the development of heterogeneities by transport of elements in excess towards areas protected from deformation where phengite bearing quartz lenses crystallise this together with the very fast recrystallisation of eclogite facies minerals results in a heterogeneous redistribution of elements at sample scale and in a chemical disequilibrium between different microdomains of hundred micron size during retrogression in the amphibolite facies coeval with long term ductile deformation the fluids act as an efficient vector to redistribute the elements from a given textural site to another and thus allow to reach at hand sample scale a new chemical equilibrium between the different crystallising phases

pseudotachylytes generated during seismic faulting and eclogitization of the deep crust pseudotachylytes are typically interpreted to have formed by frictional melting during coseismic faulting within the upper to middle crust pseudotachylytes in the bergen arcs of western norway contain microlites including omphacite garnet plagioclase and quartz this eclogite facies assemblage is stable at temperatures of about 800 c and pressures of 18 to 19 kilobars corresponding to depths of 60 kilometers or more the pseudotachylytes are exposed in grenvillian granulites that locally underwent fluid induced eclogitization and corresponding volume reduction of approximately 10 percent during the caledonian continental collision the pseudotachylytes may have formed as a result of the rapid relaxation of stresses caused by the eclogitization process

uplift of tibet from eclogites to granulites implications for the andean plateau and the variscan belt abstract using a simplified petrogenetic grid and a one dimensional thermal model to compute the evolution of the density of the crust with time the contribution to the uplift of tibet of metamorphic transitions in the lower crust is shown to be large the computations are made for a lower crust of either mafic or intermediate composition a mafic lower crust would have a mantle like density incompatible with seismological results this conclusion implies that any pre thickening gabbroic lower crust has been removed during the orogenic process a lower crust of intermediate composition would be affected by about 3 km of post thickening uplift over a few tens of millions of years this uplift is essentially the result of the eclogite to granulite transformation the resulting altitude matches the present altitude and does not require any delamination of the mantle lithosphere such a process would also explain why the neogene uplift of tibet to an average elevation of 5 km appears to have occurred without crustal shortening the same model may explain the uplift of the altiplano puna plateau which also occurred without surface shortening since about 10 ma a comparison is made with the now collapsed variscan high mountain belt for which there is evidence of a progressive increase of the temperature in the crust over tens of million years