sector trilling in cordierite and equilibrium overstepping in metamorphism the origin of sector trilling in cordierite is due to the hexagonal orthorhombic al si ordering transformation which under non equilibrium conditions proceeds via a short range ordered modulated structure the growth of these distortion waves associated with progressive ordering produces a strain field which is minimized by a cyclic distribution of symmetrically equivalent modulations sector and complexly trilled cordierites in metamorphic rocks grew as the hexagonal polymorph with a considerable degree of al si disorder the enthalpy and entropy of disorder are evaluated from recent experimental work the implication is that in metamorphic rocks substantial overstepping of stable equilibrium phase boundaries is required to nucleate hexagonal cordierite moreover its composition coexisting with other phases will also be significantly different from that of the stable ordered form

calcium and sodium exchange during hydrothermal alteration of calcic plagioclase at 400 c and 400 bars a series of experiments were conducted to measure the effect of plagioclase composition on the composition of coexisting cl dominated hydrothermal fluids assemblages containing quartz and natural plagioclase with a composition of either an60 or an82 were reacted with na ca cl fluids at 400 c and 400 bars using flexible cell hydrothermal facilities plagioclase remained homogeneous during these experiments despite the fact that homogeneous solid solutions with intermediate compositions are likely metastable with respect to mechanical mixtures at these conditions it was found that ca and na exchange between fluids and minerals appears to be reversible and highly dependent on plagioclase composition but mca m2na ratios remained constant with increasing cl for a given plagioclase composition in fact a solid solution model which approaches ideal behavior appears to account best for the chemistry of fluids coexisting with an60 and an82 plagioclase these data may have a direct bearing on hydrothermal alteration processes responsible for the chemistry of hot spring fluids at mid ocean ridges which appear to have equilibrated with metastable plagioclase solid solutions of composition an60 to an70

inertial instability and mesoscale convective systems part ii symmetric cisk in a baroclinic flow abstract numerous budget studies of organized persistent systems of convective clouds outside the tropics suggest that circulations of mesoscale proportions are important in supplying moisture to the convective clouds though the dynamical nature of mesoscale flows remains poorly defined in part i emanuel 1979 hereafter referred to as part i it is demonstrated that circulations resulting from symmetric instability of shear flows in rotating fluids have a fundamentally mesoscale character in that both ambient rotation and ageostrophic advection are necessary for instability the results of part i are here extended to include the effects of latent heat release in a conditionally unstable atmosphere using the formalism of the cisk approach it is found that the presence of shear parallel to the wave fronts introduces new wave cisk modes which are not strongly dependent on the specified vertical structure of the cumulus heating the new baroclinic modes are of mesoscale dimensions have growth rates pro

wavelet isolation of meridionally moving geopotential height perturbations near the subtropics of eastern africa and their relationship with the madden julian oscillation

circulation anomalies associated with tropical convection during northern winter abstract lagged cross correlations between outgoing longwave radiation olr and national meteorological center global analyses are utilized to isolate the preferred upper level and surface circulation anomalies associated with tropical convection during northern winter three intraseasonal time scales are studied 30 70 14 30 and 6 14 days in the 30 70 day band the upper level circulation signals are zonally elongated with zonal wavenumbers 0 2 dominant higher frequency signals are dominated by zonal wavenumbers 5 and 6 in the 14 30 day band convection over the eastern hemisphere is associated with upper level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains the strongest signals are for convection over africa australia and the eastern indian ocean only weak signals are seen for convection over indonesia in these regions of upper level easterlies olr anomalies peak prior to the maximum anomalies in wind suggesting forcing of the circulation b

formation of sapphirine and corundum in scapolitised and mg metasomatised gabbro terra nova 22 166 171 2010 abstract sapphirine mg3 41fe0 11al4 45 al4 55si1 45 o20 and corundum are found as inclusions 0 2 mm in cl rich scapolite me24 25 and plagioclase an20 24 in the metasomatised parts of the odegarden gabbro bamble sector south norway microtextural relationships suggest that the overall reaction plagioclase mg cl sapphirine corundum scapolite ca fe took place in two stages possibly related to infiltration of two metasomatic fronts gresen analyses support that the scapolitisation was combined with a strong mg metasomatism and removal of fe and ca on a whole rock scale the ferromagnesian minerals associated with sapphirine in the scapolite metagabbro have especially high mg ratios orthopyroxene mg 0 96 phlogopite mg 0 95 amphibole mg 0 81 0 87 clinopyroxene mg 0 95 this is much higher than in biotite mg 0 60 and clinopyroxene mg 0 78 0 81 in the unscapolitised parts of the gabbro and comparable with that found in sapphirine bearing orthoamphibole cordierite schists in the region suggesting that they also formed by metasomatism a metasomatic origin for the sapphirine has consequences for models of crustal growth and metamorphic history

cross equatorial response to middle latitude forcing in a zonally varying basic state abstract a nonlinear model based on the shallow water equations is used to study cross equatorial propagation of forced waves in the presence of a longitudinally varying time mean basic state zonal wind field it is found that global scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes however if the longitudinally asymmetric basic state includes a duet in which the zonal winds are westerly waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally symmetric mean zonal wind remains easterly in the equatorial region the amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct the existence and annual variations of a westerly duct region in the upper troposphere in the eastern pacific appear to account for some features of the low frequency variability in the no

a review of cold fronts with prefrontal troughs and wind shifts the conceptual model of a classical surface based cold front consists of a sharp temperature decrease coincident with a pressure trough and a distinct wind shift at the surface many cold fronts however do not conform to this model time series at a single surface station may possess a pressure trough and wind shift in the warm air preceding the cold front hereafter called a prefrontal trough and prefrontal wind shift respectively although many authors have recognized these prefrontal features previously a review of the responsible mechanisms has not been performed to date this paper presents such a review ten disparate mechanisms with different frontal structures have been identified from the previous literature these mechanisms include those external to the front i e those not directly associated with the cold front itself synoptic scale forcing interaction with lee troughs drylines interaction with fronts in the mid and upper troposphere and frontogenesis associated with inhomogeneities in the prefrontal air mechanisms internal to the front i e those directly associated with the structure and dynamics of the front include the following surface friction frontogenesis acting on alongfront temperature gradients moist processes descent of air ascent of air at the front and generation of prefrontal bores gravity waves given the gaps in our knowledge of the structure evolution and dynamics of surface cold fronts this paper closes with an admonition for improving the links between theory observations and modeling to advance understanding and develop better conceptual models of cold fronts with the goal of improving both scientific understanding and operational forecasting

the tropical extratropical interaction between high frequency transients and the madden julian oscillation abstract the interaction between high frequency transient disturbances and convection and the madden julian oscillation mjo is investigated using ncep ncar reanalysis and satellite outgoing longwave radiation data for 15 northern winters during the phase of the mjo with enhanced convection over the east indian ocean and indonesia and suppressed convection over the south pacific convergence zone both the asian pacific jet and the region of upper tropospheric tropical easterlies over the warm pool are displaced westward these changes in the basic state lead to a weaker or leakier waveguide in the asian pacific jet with a westward displaced forbidden region of tropical easterlies such that high frequency transient waves propagate equatorward into the deep tropics over the central pacific near the date line as these waves induce convection in the region of ascent and reduced static stability ahead of the upper level cyclonic disturbances there is an enhancement of high frequency convective var

mechanisms and rates of plagioclase carbonation reactions abstract plagioclase is one of the most abundant sources of calcium in the earth s crust and it may play an important role for co2 storage this study address the carbonation of anorthite rich plagioclase an67 an73 in a system with fluid transport and under stagnant conditions a combined approach of flow through column and batch experiments has been used experimental conditions ranging from 100 to 250 c and 20 to 120 bar and different preparations of the starting material were applied the overall carbonation reaction consists of plagioclase dissolution coupled to a number of precipitation reactions the flow through column experiments at 250 c showed stoichiometric dissolution of the plagioclase al hydroxide proto al hydroxide nucleated on the plagioclase as the first phase to precipitate a secondary porosity developed between the shrinking plagioclase and the enclosing proto al hydroxide calcite as the second phase to precipitate filled the primary pore space a reaction front was developed separating the zone at the inlet where all the plagioclase had dissolved and the less reacted outlet of the column redissolution of the calcite and formation of euhedral boehmite crystals occurred when a sufficient amount of plagioclase had dissolved clay minerals were not precipitated in the column experiments between 11 and 30 of the plagioclase was dissolved within 72 168 h of reaction a much higher extent of plagioclase dissolution was observed in the high pressure experiments compared to the low pressure however a smaller share of the released ca was trapped as calcite in the high pressure experiments both observations are consistent with a more rapid progression of the dissolution front at high pressure the batch experiments showed conversion of the plagioclase to a mixture of al hydroxide possibly gibbsite clays and calcite a range in conversion from below the detection limit to 91 was observed within reaction periods of 24 72 h crystallinity of the feldspar was the most important factor contributing to increased reaction rates a general positive effect of increasing temperature on the conversion is observed for all materials whereas pressure and the addition of cacl2 did not have any effect the carbonation of plagioclase at stagnant conditions is slow compared to olivine at temperatures around 200 c however industrial operations involving high fluid flows of co2 water mixtures induce gradients in ph or solute concentrations which may lead to increased reaction rates and changes in porosity permeability

effect of dry large scale vertical motions on initial mjo convective onset anomalies of eastward propagating large scale vertical motion with 30 day variability at addu city maldives move into the indian ocean from the west and are implicated in madden julian oscillation mjo convective onset using ground based radar and large scale forcing data derived from a sounding array typical profiles of environmental heating moisture sink vertical motion moisture advection and eulerian moisture tendency are computed for periods prior to those during which deep convection is prevalent and those during which moderately deep cumulonimbi do not form into deep clouds convection with 3 7 km tops is ubiquitous but present in greater numbers when tropospheric moistening occurs below 600 hpa vertical eddy convergence of moisture in shallow to moderately deep clouds is likely responsible for moistening during a 3 7 day long transition period between suppressed and active mjo conditions although moistening via evaporation of cloud condensate detrained into the environment of such clouds may also be important reduction in large scale subsidence associated with a vertical velocity structure that travels with a dry eastward propagating zonal wavenumbers 1 1 5 structure in zonal wind drives a steepening of the lapse rate below 700 hpa which supports an increase in moderately deep moist convection as the moderately deep cumulonimbi moisten the lower troposphere more deep convection develops which itself moistens the upper troposphere reduction in large scale subsidence associated with the eastward propagating feature reinforces the upper tropospheric moistening helping to then rapidly make the environment conducive to formation of large stratiform precipitation regions whose heating is critical for mjo maintenance

detailed description of deformation induced semi geostrophic frontogenesis examen dans la limite de la semi geostrophie d une variante du probleme classique de la frontogenese de surface induite par la deformation le systeme particulier d ecoulement considere constitue la reponse a un champ de deformation donne d une atmosphere barocline semi infinie stratifiee et a vorticite potentielle uniforme resultats obtention d une classe de solutions analytiques simples dans l espace geostrophique obtention d une solution explicite de l equation de sawyer eliassen relative a la circulation ageostrophique obtention d une equation autonome non lineaire dans l espace reel relative au developpement a la surface de la composante du vent alignee le long du front application aux divers aspects frontogenes a savoir l echelle temporelle du developpement du front la co occurrence des differents types frontaux la pente et le mouvement des figures frontales la structure et la force de la circulation ageostrophique et le degre de validite de l approximation semi geostrophique

discrete frontal propagation over the sierra cascade mountains and intermountain west abstract on 25 march 2006 a complex frontal system moved across the sierra cascade mountains and intensified rapidly over the intermountain west where it produced one of the strongest cold frontal passages observed in salt lake city utah during the past 25 yr observational analyses and numerical simulations by the weather research and forecast wrf model illustrate that the frontal system propagated discretely across the sierra cascade mountains and western nevada this discrete propagation occurs in a synoptic environment that features a mobile upper level cyclonic potential vorticity pv anomaly that is coupled initially with a landfalling pacific cyclone and attendant occluded front the eastward migration of the upper level cyclonic pv anomaly ultimately encourages the development of a new surface based cold front ahead of the landfalling occlusion as troughing confluence and convergence downstream of the sierra nevada intensify preexisting baroclinity over nevada trajectories show that the n

implications of trace element geochemistry for the origin of cordierite orthoamphibole rocks from orijarvi sw finland we present the first comprehensive geochemical data major elements and 31 trace elements by xrf and inaa for the metamorphic cordierite orthoamphibole anthophyllite gedrite rocks cor that occur in the early proterozoic 1 85 ga svecofennian supracrustal rocks at orijarvi finland eight samples and associated cummingtonite biotite plagioclase gneisses five samples cor 57 3 76 9 wt sio are distinguished from 50 4 61 7 wt sio by lower sc cr and co and by higher zr hf nb tth and u cor have enriched and fractionated lree 45 105x chondrites flat hree 10 21x and prominent negative eu anomalies display highly variable lree 10 90x chondrites flat hree 4 20x and mostly positive eu anomalies four of five samples for all samples concentrations of sr 18 304 ppm correlate strongly with cao 0 1 9 4 wt cor and have low concentrations of cu 10 90 ppm and moderate concentrations of zn 50 400 ppm several elemental parameters la th sc and th hf co proportions z

discrete frontal propagation in a nonconvective environment abstract surface discrete frontal propagation in a wintertime nonconvective environment is documented using conventional surface and upper air data and simulated using the psu ncar mesoscale model synoptic and mesoscale surface analyses show a cold front associated with a synoptic scale low pressure system propagating from northwest to southeast across the central united states apparently discrete frontal propagation occurs when the surface front dissipates and a new front forms approximately 500 km ahead of the original front with no compelling evidence of frontal passage in the intervening space upper air analyses indicate the infusion of three different airstreams into the frontal region resulting in the formation of a ribbon of low static stability air parallel to and several hundred kilometers in advance of the original front this static stability structure appears to be involved in the observed evolution of the front the development of precipitation over the intervening zone between the old

mg metasomatism of metagranitoids from the alps genesis and possible tectonic scenarios terra nova 24 423 436 2012 abstract mg metasomatic rocks e g whiteschists leucophyllites derived from post variscan granitoids are common in the alps previously reported field petrological geochemical and fluid inclusion data are combined to trace the genetic processes and the associated tectonic scenarios many common features can be recognised in all of the continental mg metasomatic rocks indicating that the genetic process is likely common in the entire range of the alps this process assumes highly channelised fluids derived from ultramafic rocks previously interacting with seawater that infiltrated the continental crust along strain zones and produced chromatographic fractionation of major and trace elements three tectonic scenarios involving distinct mantle sources are proposed rift related ocean continent transition continental subduction and continent continent collision all these data suggest that the mg metasomatism was diachronous and occurred at different structural levels during the alpine history

the development of upper tropospheric wind over the western hemisphere in association with mjo convective initiation abstractthis study examines the structure and driving mechanisms of upper tropospheric intraseasonal zonal wind anomalies over the western hemisphere wh during the convective initiation of the madden julian oscillation mjo over the indian ocean using composite and budget analyses the initiating mjo convection is more often associated with wh upper tropospheric intraseasonal easterly wind anomalies and when it is it tends to develop a stronger and zonally broader envelope of enhanced convection than events associated with westerly wind anomalies the wh upper tropospheric zonal wind anomaly associated with the mjo is often described as a dry kelvin wave radiated from mjo convection but the results show that both the structure and driving mechanisms are different from the ones of theoretical kelvin waves unlike the theoretical kelvin wave the zonal wind anomaly is not driven mainly by the zonal pressure gradient force and it is strongly coupled with rotational wind associated with subtropical and

cordierite formation during the experimental reaction of plagioclase with mg rich aqueous solutions the reaction between plagioclase labradorite and oligoclase and mg rich aqueous solutions was studied experimentally at hydrothermal conditions 600 700 c 2 kbar during the experiments plagioclase grains were readily converted to cordierite and quartz within 4 days the cordierite crystals had well developed polyhedral shapes but showed skeletal internal morphologies suggesting that the initial growth occurred fast under high driving force conditions in pure mgcl2 solutions 0 5 5 m plagioclase dissolution and cordierite precipitation were spatially uncoupled indicating that al was to some extent mobile in the fluid cordierite crystals formed at 700 c showed orthorhombic symmetry whereas those formed at 600 c dominantly persisted in the metastable hexagonal form suggesting a strong increase in al si ordering speed between 600 and 700 c the thermodynamic evolution of the fluid solid system ultimately resulted in stabilization of ca rich plagioclase as demonstrated by partial anorthitization of unreacted plagioclase grains cordierite was also observed to form when mg was added to a potentially albitizing na silicate bearing solution in that case cordierite precipitation appeared to be more closely coupled to plagioclase dissolution and secondary alteration of remnant plagioclase grains did not occur most likely due to armoring of the plagioclase by the cordierite overgrowth the fast reaction rates observed in our experimental study have potential implications for mg metasomatism as a rock forming process

boron isotopes in tourmaline as a tracer of metasomatic processes in the bamble sector of southern norway the bamble sector of southern norway comprises metagabbros and metasediments that were metasomatically altered to various extents during a late stage of the sveconorwegian orogeny 1 06 ga the infiltration of highly saline brines along veins led to penetrative scapolitization and albitization on a regional scale and the local deposition of fe ti oxides typical secondary mineral assemblages include either scapolite apatite amphibole phlogopite tourmaline or albite epidote calcite chlorite white mica indicating that the fluids introduced large amounts of na cl mg ca k p and b to the system metasomatic tourmalines associated with different alteration stages as identified by variations in major element composition and initial 87sr 86sr were analyzed for b isotopic compositions to constrain possible sources and the evolution of the hydrothermal fluid s measured 11b values range from 5 to 27 relative to srm 951 suggesting marine evaporites interlayered with various amounts of continental detritus and pelagic clay as a possible b source reservoir the influence of a seawater derived component is clearly indicated by the heavy b isotope signature of tourmaline related to al mg rich metapelites in contrast negative 11b values can be explained by the influence of pneumatolytic fluids associated with granitic pegmatites on a regional scale i e several km 11b values in tourmaline vary widely whereas variations within a single outcrop tens of m are typically small and can be ascribed to different generations of tourmaline related to several fluid pulses

mjo initiation in the real time multivariate mjo index abstractmadden julian oscillation mjo initiation in the real time multivariate mjo rmm index is explored through an analysis of observed case studies and composite events specific examples illustrate that both the dates of mjo initiation and the existence of the mjo itself can vary substantially among several well known mjo indices depending on whether the focus is on convection or circulation composites of primary mjo initiation events in which the rmm index rapidly increases in amplitude from a non mjo state to an mjo state are presented and are supplemented by two case studies from the 1985 86 winter season results illustrate that for primary mjo initiation events in the indian ocean rmm phase 1 slowly eastward propagating 850 hpa 200 hpa easterly westerly anomalies over the indian ocean precede the amplification of the rmm index by at least 10 days while suppressed convection over the western pacific ocean precedes the amplification by 5 days these local eastern hemispheric prede

k metasomatism and detachment related mineralization harcuvar mountains arizona the bullard detachment fault a regional low angle normal fault exposed in the harcuvar mountains of west central arizona separates lower plate mylonitic rocks and chloritic breccia from upper plate volcanic and sedimentary rocks areally extensive k metasomatism has converted upper plate mafic flows and felsic ash flow tuffs into rocks with 8 to 12 wt k 2 o 2 o and a simple k feldspar hematite quartz mineralogy the secondary k feldspar is very pure or 95 to 99 5 monoclinic and structurally similar to orthoclase differences in 18 o values between secondary k feldspar replacing sanidine phenocrysts 9 to 11 and k feldspar replacing groundmass 11 to 14 in the tuffs imply differential o exchange with migrating fluids whole rock 18 o values for tuffs 10 to 14 and mafic flows 6 to 9 do not therefore represent primary igneous values the rocks apparently became k metasomatized and 18 o enriched while interacting with low to moderate temperature neutral to alkaline oxidizing brines that accumulated in an extensional basin above the detachment fault cu au ag mineralization is concentrated in faults and fissures in metasomatized mafic flows above the detachment fault fluid inclusion studies show that mineralizing fluids had minimum temperatures of 290 to 330 c along the detachment fault 240 to 290 c in mafic flows above the detachment fault and 100 to 130 c in barite calcite mn oxide veins farther from the detachment fault the predominant mineralizing fluids near the detachment fault and in the mafic flows were saline brines with 13 to 17 equivalent wt naci more dilute brines with 6 to 12 equivalent wt naci formed the barite calcite mn oxide veins inferred 18 o values of the mineralizing fluids range from 3 for high temperature quartz sulfide veins to 5 for lower temperature barite calcite mn oxide veins the high salinities oxygen isotope compositions and geologic setting indicate that the mineralizing fluids were basinal brines the mineralizing fluids apparently evolved from early deep level reducing basin brines to a later stage marked by the influx of higher level oxidizing basin brines relatively minor amounts of less evolved lower 18 o meteoric water entered the system during the very late stages of mineralization paragenetic relations and geochemical and isotopic data indicate that mineralization was superimposed on previously k metasomatized rocks mineralization and k metasomatism may be indirectly linked however because both occurred during detachment faulting and both involved basinal brines specifically k metasomatism of upper plate units liberated elements such as cu pb zn mn sr and na that were incorporated into the mineralizing basin brines multiple fluid regimes during detachment faulting are indicated because basin brine dominated mineralization overprinted lower plate mylonitic rocks and breccia that had probably previously equilibrated with igneous or metamorphic fluids at deeper levels of the detachment system

a case study of the mechanics of extratropical influence on the initiation of the madden julian oscillation abstract mechanisms for extratropical influences on the initiation of the madden julian oscillation mjo are investigated using numerical simulations and a global reanalysis product previous simulations by a tropical channel model captured the timing and gross features of the initiations of two mjo events and suggested that the initiations were due to influences from the extratropics in this study latitudinal transport of momentum from the extratropics is found to be crucial in generating the lower tropospheric westerlies in the tropics associated with the mjo initiation the diagnoses of the zonal momentum budget for the mjo initiation region revealed that the advection by meridional winds could be important prior to the initiation of the mjo the time evolution of the wave activity identifies its source over the southern indian ocean where it grows by extracting kinetic energy from the mean flow the time scale of the lateral boundary conditions that is responsible for the mjo initiation is also inv

mg metasomatism and formation conditions of mg chlorite muscovite quartzphyllites leucophyllites of the eastern alps w hungary and their relations to alpine whiteschists the lower austroalpine orthogneiss micachist complex of the sopron fertorakos area of w hungary contains mg chlorite muscovite quartzphyllites leuco phyllite and mg chlorite bearing kyanite quartzites whose chemical compositions differ greatly from their surrounding rocks formation of leucophyllites took place in shear zones and was associated with depletion in alkalies and iron and enrichment of magnesium and h2o mg zonation of relict igneous muscovites of leucophyllites and changes in the whole rock chemical compositions suggest mg metasomatism material gains and losses have been assessed using the composition volume relationship approach proceeding from metagranite through transition rocks to leucophyllites mgo h2o feo and alkalies show continuously increasing dispersion in isocon plots with mg enrichment even in sheared gneiss not in contact with leucophyllite the metasomatic processes that formed the mg rich rocks may be similar to those responsible for the formation of high pressure whiteschists in the central and western alps the geochemical characteristics of the dora maira whiteschists italy and their country gneisses are very similar to those of the sopron leucophyllites supporting the theory that mg metasomatism produced the whiteschist chemistry on the basis of oxygen isotope compositions of relict igneous muscovites the precursor granitic rock had a 18o value around 13 proving its crustal anatectic origin the leucophyllites have whole rock oxygen isotope compositions around 8 5 which is in conflict with the theory of an mg rich sedimentary protolith rather the low 18o values reflect fluid rock interaction with a low 18o fluid quartz mineral oxygen isotope fractionations yield a metamorphic temperature of 560 30 c which agrees with earlier estimates from mineral stabilities silicon contents of phengites correspond to a metamorphic pressure of 13 gpa at this temperature indicating eclogite facies metamorphism the fluids in equilibrium with leucophyllites had oxygen isotope compositions around 7 9 similar to those calculated for the ultrahigh pressure dora maira whiteschists 7 6 further supporting the genetic link between the leucophyllites and whiteschists hydrogen isotope compositions of mixed white mica chlorite samples from leucophyllites range from 40 to 35 correlating with chlorite contents the calculated endmember chlorite and white mica have d values of 30 and 40 respectively the similar d values of the white micas in leucophyllites gneisses and metagranites suggest an overall equilibration with respect to h isotopes the calculated d value of the fluid is approximately 0 suggesting a seawater origin this conclusion was also reached for the dora maira whiteschists a possible fluid source that satisfies both metasomatic and isotopic data is dehydration of hydrothermally altered oceanic crust the mafic ultramafic complex of the alpine penninic unit underlying the austroalpine nappes is a likely candidate the subduction and subsequent dehydration of the ophiolite series would supply the mg rich fluids whose migration brought about the metasomatic alteration of the overlying gneiss micaschist complexes

geochemistry and origin of cordierite orthoamphibole gneiss and associated rocks at an archaean volcanogenic massive sulphide camp manitouwadge ontario canada abstract cordierite orthoamphibole gneiss amphibolites quartz biotite schist and calc silicate rocks occur in spatial association with archaean metamorphosed volcanogenic massive sulphide vms deposits at manitouwadge ontario trace element characteristics particularly those of the high field strength elements hfse support field relationships that most of the cordierite orthoamphibole gneisses represent metamorphosed equivalents of chlorite rich rocks that were derived hydrothermally from tholeiitic basalts as an integral part of the syngenetic ore forming processes on the archaean seafloor however a garnet rich cordierite orthoamphibole dike that is characterized by low tio2 content and high concentrations of zr y nb and ree and has single zircon pb evaporation 207 pb 206 pb ages of 2715 2743 ma may have been derived from a synvolcanic felsic dike evidently the seafloor hydrothermal alteration at manitouwadge resulted in similar alteration products from contrasting protoliths and therefore was a fluid dominant system the amphibolite lenses within the cordierite orthoamphibole gneiss also have been affected by the seafloor hydrothermal alteration and some of them most likely represent metamorphosed equivalents of calcsilicate alteration products formed on the seafloor mass balance calculations indicate that hfse and ree were mobilized during the seafloor hydrothermal alteration the mobility of hfse and ree was controlled by both their host minerals and the hydrothermal fluids in particular a significant portion of igneous zircon in the garnet rich dike has survived the seafloor hydrothermal alteration and the subsequent high grade regional metamorphism the regional metamorphism did not change the bulk rock ree characteristics but was important in redefining the mineralogy of ree trace element geochemistry of mafic metavolcanic rocks at manitouwadge are similar to those of the adjacent schreiber hemlo greenstone belt and are consistent with a volcanic island arc setting however further work is required to determine whether the manitouwadge and adjacent greenstone belts of the wawa subprovince were originally a larger continuous terrane

interactions between serpentinite devolatilization metasomatism and strike slip strain localization during deep crustal shearing in the eastern alps the greiner shear zone in the tauern window eastern alps changes from a zone of distributed dominantly sinistral shear in supracrustal rocks to a series of narrow gully forming dextral splays where it enters basement gneisses within these splays granodiorite is transformed into quartz poor biotite and or chlorite schists reflecting hydration removal of si ca and na and concentration of fe mg and al stable isotope analyses show a prominent increase in d and a decrease in 18o from granodiorite into the shear zones these changes indicate significant channelized flow of an externally derived low 18o high d fluid through the shear zones the shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the greiner zone and the stable isotope data support alteration via serpentinite derived fluid monazite in schist from one shear zone yields spot dates of 29 20 ma indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the alpine orogeny c 30 ma we suggest that alpine metamorphism of serpentinites released large amounts of high d low 18o si undersaturated fe mg saturated fluids that became channelized along prior zones of weakness in the granodiorite infiltration of this fluid facilitated growth of chlorite and biotite which in turn localized later dextral strain in the narrow splays via cleavage parallel slip this dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the eastern alps this study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis

plagioclase and epidote buffering of cation ratios in mid ocean ridge hydrothermal fluids experimental results in and near the supercritical region abstract experiments have been performed with na ca k cl fluids of seawater chlorinity and diabase basalt and plagioclase bearing mineral mixtures at 350 425 c and 250 400 bars to help constrain hydrothermal alteration processes at mid ocean ridges dissolved ca na and ph for all experiments responded systematically to differences in dissolved sio2 concentrations and the compositions of plagioclase reactants diabase alteration at low fluid rock mass ratios 0 5 to 1 produces fluids undersaturated with respect to quartz during hydration of primary olivine and orthopyroxene whereas basalt alteration under similar conditions yields fluids slightly supersaturated with respect to quartz during breakdown of glass to smectite and amphibole fluid chemistry in all experiments appears to approach a partial equilibrium state with the albite and anorthite components in plagioclase and approaches a ph consistent with plagioclase alteration to epidote trace element data from vent fluids specifically b and sr together with major element chemistry ca na sio2 ph provides evidence that the reaction zone for black smoker fluids at mid ocean ridges is composed of only slightly altered diabase and is characterized by small amounts of epidote nearly fresh plagioclase and clinopyroxene and partially to completely hydrated olivine and orthopyroxene fluids reacting with this rock may be undersaturated with respect to quartz so pressure estimates based on the quartz geobarometer should be regarded as minimums using equilibrium between plagioclase the dominant reactant and epidote the dominant reaction product in experiments we estimate that temperatures in reaction zones are in excess of 375 c for most vent systems these temperatures are higher than measured vent temperatures suggesting that hotspring fluids commonly loose heat during ascent to the seafloor

circulation anomalies associated with tropical temperate troughs in southern africa and the south west indian ocean daily rainfall variability over southern africa sa and the southwest indian ocean swio during the austral summer months has recently been described objectively for the first time using newly derived satellite products the principle mode of variability in all months is a dipole structure with bands of rainfall orientated northwest to southeast across the region these represent the location of cloud bands associated with tropical temperate troughs ttt this study objectively identifies major ttt events during november to february and on the basis of composites off ncep reanalysis data describes the associated atmospheric structure the two phases of the rainfall dipole are associated with markedly contrasting circulation patterns there are also pronounced intra seasonal variations in early summer the position of the temperate trough and ttt cloud band alternates between the swio and southwest atlantic in late summer the major ttt axis lies preferentially over the swio associated with an eastward displacement in the indian ocean high in all months positive events in which the ttt cloud band lies primarily over the swio are associated with large scale moisture flux anomalies in which convergent fluxes form a pronounced poleward flux along the cloud band this suggests that ttt events are a major mechanism of poleward transfer of energy and momentum moisture transport occurs along three principle paths 1 the northern or central indian ocean where anomalous fluxes extend eastward to the maritime continent 2 south equatorial africa and the equatorial atlantic 3 from the south within a cyclonic flow around the tropical temperate trough the relative importance of 2 is greatest in late summer thus synoptic scale ttt events over sa swio often result from large scale planetary circulation patterns hovmoeller plots show that ttt development coincides with enhanced tropical convection between 10 30 e itself exhibiting periodicity of around 5 days and often with convergence of eastward and westward propagating convection around 40 e harmonic analysis of 200 hpa geopotential anomalies show that ttt features are forced by a specific zonally asymmetric wave pattern with wave 5 dominant or significant in all months except february when quasi stationary waves 1 2 and 3 dominate these findings illustrate the importance of tropical and extratropical dynamics in understanding ttt events finally it is suggested that in november januar ttt rainfall over sa swio may be in phase with similar rainfall dipole structures observed in the south pacific and south atlantic convergence zones

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

reaction of plagioclase feldspars with co2 under hydrothermal conditions abstract geological storage of co 2 in plagioclase bearing sediments granitic rocks and fractured basalts is expected to have a variety of geochemical and geomechanical effects including mineral trapping and porosity permeability changes the amount of co 2 trapped by mineralisation and the extent of any changes in host rock transport or mechanical properties depend on rock composition to date studies of mineralisation have mainly been based on dissolution and precipitation experiments performed at ambient surface conditions or at slightly elevated temperature and pressure however the reactions that occur under in situ conditions are poorly constrained in an attempt to determine the secondary phases formed in the plagioclase co 2 water system under such conditions we performed a set of batch experiments at temperatures in the range 200 300 c using carbon dioxide pressures from 0 4 to 15 mpa we investigated reaction of anorthite and albite which are expected to precipitate calcite and kaolinite and dawsonite and quartz respectively however in most of our experiments reactions precipitating clays kaolinite and smectite or illite boehmite and a mg ni fe hydrotalcite like phase dominated the nickel being derived from the reaction vessel little or no carbonate and no dawsonite were detected additional feldspar free control experiments employing mg rich brine showed that carbonates would be preserved in our feldspar experiments if formed but that a carbonate substrate is needed to promote precipitation since the secondary phases formed in our plagioclase experiments are stable under a wide range of conditions we expect that they will also form under co 2 storage systems with suitable fluid rock composition from our results we conclude that clay precipitation can proceed or accompany carbonate precipitation depending on the availability of carbonate substrate though an artefact in our experiments in the context of subsurface alkaline waste injection hydrotalcite may play a positive role here by immobilising heavy metals while carbonates will mineralise the co 2

some aspects of western hemisphere circulation and the madden julian oscillation abstractalthough the greatest variance in convection associated with the madden julian oscillation mjo occurs over the indo pacific warm pool the mjo is associated with substantial circulation patterns in the tropics and the extratropics of the western hemisphere reanalysis data suggest that upper tropospheric easterly wind anomalies on the equator between 40 and 140 w precede 86 of active convective phases of mjo events greater than one standard deviation in amplitude over the indian ocean basin during the northern hemisphere winter composites of those mjo events that are preceded by westerly wind anomalies and those events preceded by easterly wind anomalies are compared results show that those events that are preceded by westerly wind anomalies fail to thrive and do not yield the amplitude in convection or the canonical atmospheric circulation response that is associated with those preceded by easterly wind the composite of events preceded by easterly winds reveals that these winds amplify coi

the formation of multiple fronts using two dimensional semi geostrophic frontogenesis models and three dimensional semi geostrophic baroclinic wave models it is shown that atmospheric development in the presence of non uniformities in pre existing temperature distributions may be expected to lead to the frequent occurrence of multiple frontal structures in general such non uniformities in the temperature distribution will be important if they significantly change the ambient temperature gradient the frontal structures associated with the irregularities tend to be very shallow they are possible candidates for the triggering mechanism for frontal troughs well behind a cold front and for shallow rainbands ahead of such a front however it seems that a separate mechanism is still necessary for the production of the middle level banded structures that are frequently observed

interactions between the tropical iso and midlatitude low frequency flow in this study we investigate the interaction between the tropical intraseasonal oscillation iso and midlatitude atmospheric low frequency variability using observational data and numerical models with a special emphasis on the role of the synoptic eddy feedback a statistical closure for the synoptic eddy to low frequency flow feedback is constructed based on a singular value decomposition svd method with observational data applying this statistical closure to a barotropic model and a baroclinic 2 layer model we study the role of the synoptic eddy feedback in the midlatitude response to the tropical iso forcing both observational and modeling studies show that the strongest synoptic eddy forcing appears at the pacific and atlantic storm track regions and the synoptic eddy exerts a positive feedback to the midlatitude low frequency flow induced by tropical iso forcing our numerical experiments demonstrate the possible role of midlatitude disturbance forcing in the iso initiation at the equator the signal of the midlatitude perturbations propagates southeastward in the form of a rossby wave package it may reach the equator within several days under either easterly or westerly basic flow regimes the response at the equator has observed iso like structure and eastward propagation characteristics

warm and occluded fronts in two dimensional moist baroclinic instability the two dimensional eady mode of baroclinic instability exhibits a strong cold front structure after a period of development using semi geostrophic equations excluding moist processes indeed the surface wave has a single centre of cyclonic vorticity on the cold side of the warm air anomaly here results are presented from a semi geostrophic numerical model including moist effects which predicts an eady wave with a cold and a warm front associated with two centres of surface vorticity located on either side of the warm anomaly the ascent regions are taken to be saturated and close to moist neutral which in this baroclinic environment corresponds to a condition of zero equivalent potential vorticity the descent is taken to be unsaturated this development of a structure resembling a warm front occurs only when the moist effects become dominant within a pre existing weak dry eady mode using the same condensation representation starting from an extremely small and random amplitude disturbance a pure moist eady mode develops with a single vorticity maximum in the form of a cold front in nature it is likely that often the moisture becomes dominant after a period albeit sometimes a short period of essentially unsaturated growth although observational evidence is limited therefore the process of warm frontogenesis described here may be a contributory factor to those minority of mid latitude cyclones which exhibit a strong warm front the model indicates that the warm front moves more slowly than the cold front resulting in a cold occlusion process these investigations require a detailed examination of the initial growth of small amplitude disturbances near the limit of neutral moist ascent i e pure moist modes results of previous such calculations using an analytical 2 level model are confirmed here using a numerical multi level model the more accurate estimates obtained here show that the finite growth rate in the limit of zero equivalent potential vorticity has a value of 1 9 times the dry value compared with the 2 4 fold increase given by the 2 level model

mesoscale atmospheric dynamics and modeling of rainfall fields a nonuniform potential vorticity model for frontogenesis is used to study the effects of height dependent inhomogeneities in the potential temperature and potential vorticity fields at the mesoscale the model simulation results show that these irregularities induce in the vertical velocity field mesoscale patterns which have considerable vertical extent it is suggested that these mesoscale inhomogeneities may be possible causes for the high degree of organization of precipitation fields and the formation of middle level rainbands

the 1985 86 intraseasonal oscillation and the role of the extratropics abstract an intraseasonal oscillation that occurred in the 1985 86 northern winter is documented in this study the tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the indian ocean into the central pacific the time evolution of the upper tropospheric circulation patterns instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation is characterized by a series of wave patterns in the northern hemisphere and does not complete the cycle around the globe the familiar moist kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind height field streamfunction and potential vorticity only in the lower troposphere near the date line is the convincing evidence for its existence found a scenario for the intraseasonal oscillation which is suggested by the analysis includes

diabatically driven discrete propagation of surface fronts a numerical analysis discrete frontal propagation has been identified as a process whereby a surface front discontinuously moves forward without evidence of frontal passage across a mesoscale region numerical simulations are employed to examine the upper level evolution of a discrete frontal propagation event and to explore the processes that were responsible for the discrete movement model results indicate that a frontal pressure trough was not able to penetrate through a deep surface based layer of cool air created by a precipitating convective system several hundred kilometers in advance of the front meanwhile a new low level baroclinic zone formed well ahead of the front along the southern side of the cool layer as the midlevel front moved continuously over the cool layer a new low level front developed in the new baroclinic zone and the original low level front dissipated at the surface the simulated front did not pass through the cool layer frontogenesis terms reveal that the prefrontal circulation that becomes the new frontal circulation initially forms directly from diabatic frontogenesis daytime heating in the prefrontal boundary layer and cooling from thunderstorms combine to create a thermal gradient and a mesoscale pressure perturbation winds turn in response to the altered pressure field and form a convergent boundary resulting in kinematic frontogenesis the boundary subsequently undergoes rapid intensification sensitivity studies were conducted in which latent heating due to precipitation was withheld and the influence of clouds on the radiation scheme was ignored in a simulation with both of these effects withheld the original front passes continuously through the region that is there is no discrete propagation thus diabatic processes associated with a large complex of thunderstorms were necessary to induce the discrete frontal propagation in this case this conclusion contrasts with previous studies where fronts were observed to propagate discretely in dry environments

role of the atmospheric mean state on the initiation of the madden julian oscillation in a tropical channel model tropical channel models defined as models that are global in the zonal direction but bounded in the meridional direction are particularly useful for simulating the madden julian oscillation mjo and understanding its physical and dynamical basis influences from the extratropics through the lateral boundaries have been found to be essential to the reproduction of the initiation of certain mjo events this led to a hypothesis that multi year simulations using a tropical channel model would reproduce reasonable mjo statistics under the influence of prescribed lateral boundary conditions derived from global reanalyses interestingly the mjo statistics in such a multi year simulation by a high resolution tropical channel model are not better than those from global climate models the error in the atmospheric mean state is found to be a possible reason for the poor mjo statistics in the simulation nevertheless even with a large error in the mean state the multi year simulation captures two mjo events previously found to be initiated by extratropical influences however the model does not reproduce a third event whose initiation is not directly influenced by the extratropics this implies that in the absence of dynamical interactions between the mjo and the lateral boundary conditions the error in the mean state could be sufficient to prevent the mjo initiation to explore this third mjo event further a series of sensitivity tests are conducted these tests show that the simulation of this event is neither critically influenced by the cumulus parameterization employed nor the initial conditions when the model is integrated 2 weeks prior to the mjo initiation the model captures this event when the mjo signal is already present in the initial conditions the use of high resolution sea surface temperature does not improve the simulation of the third mjo event a higher resolution nested domain covering the indo pacific warm pool region and including a cloud system resolving domain over the indonesian maritime continent has little effect on the mjo initiation over the indian ocean in 2 weeks the error in the simulation is comparable to the climate error the role of the simulated mjo on the mean state is also explored implications and limitations of these results are discussed

influence of the madden julian oscillation on southern african summer rainfall composite maps of outgoing longwave radiation olr anomalies over the madden julian oscillation mjo cycle show marked intraseasonal fluctuations over southern africa south of 15 s large scale convective clusters are seen to propagate eastward and then northward over the continent mainly between 10 and 20 s the corresponding response of the rainfall field presents the alternation over the cycle of dry and humid phases which are both significant moisture flux anomalies indicate an intraseasonal modulation of the midtropospheric easterly flow over the congo basin at 700 hpa these fluctuations are coupled to meridional flux anomalies that extend from the tropical to the subtropical austral latitudes and favor occurrences of wet or dry conditions over the domain though statistically significant the influence of the mjo on southern africa is however not homogeneous spatially and only the tropical areas exhibit sharp periodicities in the 30 60 day period range the olr dipole observed in previous studies at the interannual and synoptic time scales between the hinterland parts of southern africa and the southwestern indian ocean in the north of madagascar is investigated next as it also shows strong fluctuations at the intraseasonal time scale the study points out that the dipole is partly influenced by the mjo though the strongest periodicities are found for slightly longer periods 35 80 days than those typically associated with the oscillation the forcing of the mjo on the olr dipole though significant remains thus partial

mass transfer and porosity evolution during low temperature water rock interaction in gneisses of the simano nappe arvigo val calanca swiss alps late alpine fissures and fractures in amphibolite facies basement gneisses at arvigo val calanca swiss alps show distinct cm sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high grade gneiss assemblages the process of selvage or reaction vein formation occurred in the brittle deformation regime and at temperatures characteristic of first the prehnite pumpellyite facies and then later of the zeolite facies the vein formation occurred during uplift and cooling at very late stages of the alpine orogeny the reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space the central zone of the arvigo veins contains an early assemblage with epidote prehnite and chlorite and a late succession sequence of various species of zeolite the veins of the arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate ca zeolite this is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of ca zeolite species vein formation during late uplift and cooling of the alps occurred at continuously decreasing t and at hydrostatic pressure 1 coexisting prehnite epidote records temperatures of 330 380 c 2 chlorite formation at temperature of 333 32 c and 3 formation of zeolites 250 c in the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss in addition to albitisation chloritisation of biotite is the second important reaction in the alteration process the reactions release components for the formation of ca al silicates the water rock interaction is associated with a depletion of al si ca fe and k in the altered wall rock the overall reaction is associated with an increase in porosity of up to 14 2 2 2 in the selvage zone altered wall rock caused by the volume decrease during albitisation and the removal of biotite the propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution reprecipitation mechanism zeolite formation is tied to the plagioclase alteration reaction in the rock matrix which releases components for zeolite formation to a co2 poor aqueous liquid

timing and nature of fluid flow and alteration during mesoproterozoic shear zone formation olary domain south australia the development of shear zones at mid crustal levels in the proterozoic willyama supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration monazite dating of shear zone fabrics reveal that they formed at 1582 22 ma at the end of the olarian d3 deformational event and immediately prior to the emplacement of regional s type granites two stages of fluid flow are identified in the area first an albitizing event which involved the addition of na and loss of si k and fe and a second phase of calcsilicate alteration with additions of ca fe mg and si and removal of na fluid fluxes calculated for albitization and calcsilicate alteration were 5 56 109 to 1 02 1010 mol m 2 and 2 57 108 5 20 109 mol m 2 respectively these fluxes are consistent with estimates for fluid flow through mid crustal shear zones in other terranes the fluids associated with shearing and alteration are calculated to have 18o and d values ranging between 8 and 11 and 33 and 42 respectively and nd values between 2 24 and 8 11 our results indicate that fluids were derived from metamorphic dehydration of the willyama supergroup metasediments fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent retrograde fluid flow event thus the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times prior to regional granite formation during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing

35 ma old ultrahigh pressure metamorphism and evidence for very rapid exhumation in the dora maira massif western alps abstract ion microprobe shrimp data on zircons from various rock types of an ultrahigh pressure uhp metamorphic whiteschist type pyrope quartzite lens of the dora maira massif dmm consistently show domains giving a late eocene age of 35 4 1 0 ma which is taken as the age of uhp metamorphism these domains partially replace the older oscillatory zoning pattern of the zircons formed during primary magmatic crystallization at about 275 ma zircons of a metagranitic country rock next to the uhp metamorphic lens have these primary features best preserved all zircons measured also yield intermediate ages between 275 and 35 ma with a statistical concentration between 260 and 210 ma thus the uniformity of the initial zircon population both in the lens and the country rock evidences a common protolith that is a granite intruded during the late herynian while the intermediate ages are at least partly due to incomplete resetting of the zircons during uhp metamorphism those in the 260 210 ma range may be related to rifting episodes in the permotriassic the mg rich chemistry of the whiteschist lenses is due to local metasomatic alterations of the granite perhaps by fluids derived from evaporitic sediments dating as early as the permotriassic as well the more pervasive resetting of zircon ages during uhp metamorphism in the pyrope quartzite lenses is explained by the ubiquity of fluids and or melts produced during subduction by a series of dehydration reactions that occurred only in the more hydrous mg rich protoliths and not in their drier granitic neighborhood fission track ages determined partly on the same zircon samples yielding 29 9 1 4 ma mark the time when the uhpm unit had reached about 290 c at a shallow location within the crust thus exhumation over a vertical distance of about 120 km must have occurred within about 5 6 ma indicating an average uplift rate of about 20 24 km ma and an average cooling rate of about 85 100 c ma the radiometric data obtained do not lend any support to an eo alpine cretaceous subduction event so that deep subduction and immediately following exhumation all took place during early to mid tertiary time this scenario seems to apply to large portions of the western and central alps as well calling for drastic geodynamic reinterpretations of these parts of the alps

microstructural evolution during experimental albitization of k rich alkali feldspar crystals of k feldspar c2 m in contact with highly concentrated aqueous nacl solutions at 500 c and 200 mpa are pseudomorphically replaced by high albite c bar 1 as a result of an interface coupled dissolution reprecipitation process the reaction occurs at an extremely sharp reaction front 10 nm and involves the complete breakdown of the initial framework structure this results in the release of tetrahedrally incorporated elements such as fe3 and ti4 and a significant increase in si al disorder across the reaction interface the evolving microstructure is controlled by crystallographic relations between the phases this leads to highly anisotropic sawtooth shaped intergrowths of albite and initial k feldspar resulting in the least structural misfit between the two framework structures as a result the newly formed interfaces appear to be semicoherent and cracks across the reaction fronts even indicate elastic strain the reaction produces 2 distinctive albite types albite 1 and albite 2 both are polycrystalline with albite 2 showing significantly larger subgrain sizes this indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product the reaction also produces a highly porous rim however the porosity is not evenly distributed resulting in a porous albite 1 and a non porous albite 2 that mostly surrounds large euhedral pores despite the substantial volume fraction of porosity in albite 1 no significant 3d interconnectivity could be detected making the presence of a pervasive porosity unlikely however the result of coarsening is the continuous modification of the 3d porosity distribution this could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved

the role of global circumnavigating mode in the mjo initiation and propagation a series of convection permitting regional model simulations are used to study the influences of intraseasonal forcings from the periphery of the tropical indian ocean on the october 2011 mjo event well observed during the dynamics of the madden julian oscillation dynamo field campaign these sensitivity experiments demonstrate the predominant role of a global circumnavigating mode in the initiation and propagation of this mjo event although the regional framework would not completely rule out influences from the extratropics through the western boundary of the model domain it is found that filtering out intraseasonal forcing leads to the absence of kelvin waves which may reduce moisture transport and weakened lower level convergence at the leading edge of the westerlies and further leads to diminishing mjo signatures in these sensitivity experiments meanwhile for the same regional domain initiated two weeks before the onset of the mjo convection there is little impact of whether or not the global mjo signals retained in the initial conditions on the other hand the removal of the global mjo signals from the lateral boundary conditions will not affect the propagation of the mjo after it has been initiated in the regional model domain

precipitation banding in idealized baroclinic waves abstractmoist idealized baroclinic wave simulations show the development of precipitation bands from a zonally uniform initial midlatitude jet for a frictionless lower boundary and with no latent heat release or surface heat and moisture fluxes warm advection is strong and a bent back warm front forms although a narrow vertical velocity maximum forms within the area of synoptic scale ascent near the triple point only a wide warm frontal band forms as surface roughness length increases between simulations to that of an ocean then a land surface warm advection is reduced and the cold front becomes stronger relative to the warm front a separate narrow rainband forms along the cold front which is more intense and farther removed from the wide warm frontal band when roughness length is greater in the simulation with roughness length appropriate to the ocean after the narrow band decays the precipitation becomes oriented along the warm conveyor belt in the warm sector when latent heat release is in

whiteschists and orthoamphibole cordierite rocks and the p t t path of the modum complex south norway abstract this paper describes the second known occurrence of whiteschist from norway whiteschists and orthoamphibole cordierite rocks which can both be described in the m f ash system are found in the modum complex together with albitites in contact zones between metagabbros and supracrustals they are formed due to extensive hydrothermal activity bulk rock and mineral chemistry define a bimodal fe mg distribution talc kyanite schists and fe poor orthoamphibole cordierite rocks form a leucocratic group and fe rich orthoamphibole cordierite rocks a melanocratic group the break down of an early orthoamphibole cordierite paragenesis to a later talc kyanite paragenesis indicates a cooling path at isobaric conditions or under increasing pressure the temperature pressure regime is of the order of 600 750 c and 6 8 kb reaction textures with talc albite kyanite forming pseudomorphs after gedrite indicate excess albite these nonisochemical reactions indicate the presence of an active na bearing fluid at deep levels in the crust

the replacement of plagioclase feldspars by albite observations from hydrothermal experiments oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600 c and 2 kbars the replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation reaction rims of albite up to 50 m thick can be readily achieved within 14 days re equilibration of plagioclase in an 18o enriched sodium and silica bearing solution results in oxygen isotope redistribution within the feldspar framework structure the observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface coupled dissolution reprecipitation mechanism chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major minor and trace elements also including elements such as al and ti which are commonly regarded as immobile during hydrothermal alteration the results contribute to developing our understanding of the close association between large scale albitisation and secondary ore mineralisation which is common in nature

intraseasonal variability in a dry atmospheric model abstract a long integration of a primitive equation dry atmospheric model with time independent forcing under boreal winter conditions is analyzed a variety of techniques such as time filtering space time spectral analysis and lag regressions are used to identify tropical waves it is evident that oscillations with intraseasonal time scales and a kelvin wave structure exist in the model tropical atmosphere coherent eastward propagations in the 250 hpa velocity potential and zonal wind are found with a speed of about 15 m s 1 the oscillation is stronger in the eastern hemisphere than in the western hemisphere interactions between the tropical and extratropical flows are found to be responsible for the simulated intraseasonal variability wave activity flux analysis reveals that a tropical influence occurs in the north pacific region where a northeastward wave activity flux is found associated with the tropical divergent flow in the western and central pacific in the north atlantic sector on the ot

the spectrum of convectively coupled kelvin waves and the madden julian oscillation in regions of low level easterly and westerly background flow abstractthe zonal wavenumber frequency power spectrum of outgoing longwave radiation in the global tropics suggests that power in convectively coupled kelvin waves and the madden julian oscillation mjo is organized into two distinct spectral peaks with a minimum in power in between this work demonstrates that integration of wavelet power in the wavenumber frequency domain over geographical regions of moderate trade winds yields a similar pronounced spectral gap between these peaks in contrast integration over regions of background low level westerly wind yields a continuum of power with no gap between the mjo and kelvin bands results further show that signals in tropical convection are redder in frequency in these low level westerly wind zones confirming that kelvin waves tend to propagate more slowly eastward over the warm pool than other parts of the world results are consistent with the perspective that portions of disturbances labeled as kelvin waves and the mjo that are proximate to kelvin wa

composite intraseasonal oscillations of convection over southern africa abstract intraseasonal rainfall variability over the summer rainfall region of south africa is studied spectral analysis of an areas precipitation minus evaporation index and a co located outgoing longwave radiation olr index over central south africa reveal a dominant oscillation of 20 35 days major wet spells are linked to a host of external factors including midlatitude and equatorial waves and local energy sources hovmoller analysis at 25 s describes a wide variety of convective characteristics the most frequent mode being stationary followed in descending order by eastward and westward propagating systems a composite analysis of 16 intraseasonal oscillation iso cases reveals a tropically initiated signal in the water vapor flux wvf anomaly field a westward moisture flux is found over the central indian ocean 10 15 days before the wet spell over southern africa wvf convergence from the southwestern indian ocean and southern mozambique channel together with ridging of an anticyclone fro

partial eclogitisation of gabbroic rocks in a late precambrian subduction zone zambia prograde metamorphism triggered by fluid infiltration gabbros and eclogites occur closely associated in a 200 km long and up to 40 km wide area of the zambezi belt in central zambia this area is interpreted to represent part of a late precambrian suture zone with the mafic rocks being relics of subducted oceanic crust gradual stages of prograde transformation from gabbro to eclogite are preserved by disequilibrium textures of incomplete reactions this resulted in kyanite omphacite bearing assemblages for eclogites that have al poor bulk compositions undeformed eclogites typically preserve features of a former gabbroic texture reflected by replacements of plagioclase and magmatic pyroxene by eclogite facies minerals textures of deformed eclogites range from sheared porphyroclastic to porphyroblastic relics of magmatic pyroxene are common and complete eclogitisation occurred only in millimetre to centimetre scale domains in most of the rocks no evidence for prograde blueschist or amphibolite facies mineral assemblages was found in eclogites in contrast the fine grained intergrowth of omphacite garnet kyanite and quartz which replace former plagioclase or was formed in the pressure shadow of magmatic pyroxene relics indicates that eclogitisation might have affected the gabbroic protoliths directly without any significant intervening metamorphic reactions eclogitisation took place under p t conditions of 630 690 degreesc and 26 28 kbar suggesting a large overstepping 10 kbar of reaction boundaries eclogitisation was initialised and accompanied by a channelised fluid flow resulting in veins with large subhedral grains of omphacite kyanite and garnet the gabbro to eclogite transformation was enhanced by a fluid which allowed the necessary material transport for the dissolution precipitation mechanism that characterises the metamorphic mineral replacements the process of eclogitisation was limited by reaction kinetics and dissolution precipitation rates rather than by the metamorphic p t conditions even though ductile deformation occurred and equilibrium phase boundaries were overstepped the infiltration of fluids was necessary for triggering the gabbro to eclogite transformation