h2o fluid saturated melting of subducted continental crust facilitates exhumation of ultrahigh pressure rocks in continental subduction zones we present two dimensional numerical models of plate subduction and collision inspired by the scandinavian caledonian orogeny to investigate the possible impact of continental crust partial melting on the exhumation of ultra high pressure metamorphic rocks three possible reactions were tested low temperature solidus representing h2o fluid saturated partial melting and two end member reaction curves for dehydration melting thermo mechanical effects of partial melting were implemented as 1 a viscosity decrease as a determined rheologically critical melt percentage was reached here 0 1 2 a change in effective heat capacity and adiabatic heating cooling accounting for a latent heat term in the heat equation among the 3 tested reactions only h2o fluid saturated partial melting drastically modifies the collision dynamics from the non melting reference model holding all other parameters constant a substantially low general viscosity truncation here 1017 pa s is needed to properly resolve the effect of partial melting on deep collision processes low temperature melting indeed induces the development of a low viscosity buoyant plume prior to slab detachment where migmatites exhume from uhp conditions at rates and with pressure temperature paths similar to the natural values acknowledged for the norwegian caledonides high temperature melting has no drastic influence on early collision dynamics while positive buoyancy remains the first order driver for the exhumation of buried continental rocks exhumation initiates in these cases with eduction subsequent to slab detachment melting and formation of a migmatite plume can later occur along decompression path while continental crust undergoes thermal reequilibration at temperatures above 900 c some of the partially molten material can also relaminate in the overriding plate rather than exhume within the collision zone even if minor in terms of amount of magma produced h2o fluid saturated partial melting at uhp conditions could therefore have a dramatic rheological effect and actually limits continental rocks subduction and facilitates their exhumation

global variations of thermospheric winds and temperatures caused by substorm energy injection two numerical simulations of the thermospheric response to magnetospheric energy injection have been performed using a zonally averaged time dependent model of neutral composition dynamics and energy budget the simulations are distinguished by the duration of the source the first simulation has an energy injection of 1 hour representative of substorm type forcing and the second one has a 12 hour energy injection representative of main storm type forcing they were performed under the condition of equinox at solar minimum in the first simulation large scale atmospheric gravity waves agws generated by the substorm energy via joule heating of ionospheric currents are clearly identified in the wind field in a meridional plane as well as in the temporal and spacial variations of the total energy density of air above about 130 km height these waves reach the equator after about 3 hours and propagate into the opposite hemisphere the horizontal propagation speed is close to the speed of sound for example roughly 440 m s at about 150 km altitude and 670 m s at about 260 km altitude snapshots of the wind system affected by the substorm energy injection show a four cell pattern between the poles above 260 km the cells have the opposite rotational direction to those below these small scale features in the wind system are indicative of the internal atmospheric gravity waves with the vertical phase propagation from a term analysis of the energy conservation equation it is identified that the dominant energy process associated with the propagation of agws is adiabatic compressional heating and or expansive cooling process it can be concluded that the energy oscillations at middle and low latitude are mainly produced by agws propagating from high latitude during the substorm the second simulation indicated that horizontal and vertical advections vertical heat conduction and infrared radiative cooling by nitric oxide are important in addition to adiabatic compressional heating and or expansive cooling it is suggested that short duration energy injection preferentially generates agws which dominate the energy oscillations at low latitudes through adiabatic heating and cooling long duration energy injection is more effective in generating a meridional circulation which transfers energy by both advective and adiabatic processes

high temperature deformation during continental margin subduction exhumation the ultrahigh pressure western gneiss region of norway abstract a new dataset for the high pressure to ultrahigh pressure western gneiss region allows the definition of distinct structural and petrological domains much of the study area is an e dipping homocline with e plunging lineations that exposes progressively deeper more strongly deformed more eclogite rich structural levels westward although eclogites crop out across the wgr scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area the scandian reworking increases westward culminating in strong scandian fabrics with only isolated pockets of older structures the dominant scandian deformation was coaxial e w stretching the sinistrally sheared more trondelag fault complex and nordfjord mylonitic shear zone bound these rocks to the north and south there was moderate top e amphibolite facies deformation associated with translation of the allochthons over the basement along its eastern edge and the nordfjord sogn detachment zone underwent strong lower amphibolite facies to greenschist facies top w shearing a northwestward increase in exhumation related melting is indicated by leucosomes with hornblende plagioclase and scandian sphene in the western 2 3 of the study area exhumation related amphibolite facies symplectite formation in quartzofeldspathic gneiss postdated most scandian deformation further deformation was restricted to slip along biotite rich foliation planes and minor local folding that the western gneiss region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation implies that continental crust in general need not undergo pervasive deformation during subduction

ionospheric annual anomaly new insights to the physical mechanisms the ionospheric annual anomaly or nonseasonal anomaly of the ionosphere is characterized by globally increased ionization in december solstice than in june solstice though this phenomenon was reported several decades ago the causal mechanisms have not been fully understood till today in this paper the f2 layer peak electron density nmf2 data from formosa satellite 3 constellation observing system for meteorology ionosphere and climate radio occultation observations during the low solar activity year 2009 were systematically analyzed to investigate the physical mechanisms responsible for annual anomaly and its local time latitudinal and longitudinal variability it is found that the annual anomaly is primarily dominant at southern hemisphere at all local times with significant enhancements at equatorial ionization anomaly crest latitudes during noon to afternoon hours and at high latitudes during nighttimes the annual anomaly in northern hemisphere occurs with relatively smaller magnitudes and confined only to morning to early afternoon hours 08 14 lt this study brings out the important roles of effective neutral winds due to the geomagnetic field configuration and the offset between geomagnetic equator and subsolar point for the enhanced plasma density in the southern hemisphere during december that majorly contributes to the ionospheric annual anomaly these results provide new insights to the responsible mechanisms behind the ionospheric annual anomaly and its local time latitudinal and longitudinal variation

partial melting of metagreywackes part ii compositions of minerals and melts a series of experiments on the fluid absent melting of a quartz rich aluminous metagreywacke has been carried out in this paper we report the chemical composition of the phases present in the experimental charges as determined by electron microprobe this analytical work includes biotite plagioclase orthopyroxene garnet cordierite hercynite staurolite gedrite oxide and glass over the range 100 1000 mpa 780 1025 c biotites are na and mg rich with ti contents increasing with temperature the compositions of plagioclase range from an17 to an35 with a significant orthoclase component and are always different from the starting minerals at high temperature plagioclase crystals correspond to ternary feldspars with or contents in the range 11 20 mol garnets are almandine pyrope grossular spessartine solid solutions with a regular and significant increase of the grossular content with pressure all glasses are silicic sio2 67 6 74 4 wt peraluminous and leucocratic feo mgo 0 9 2 9 wt with a bulk composition close to that of peraluminous leucogranites even for degrees of melting as high as 60 vol with increasing pressure sio2 contents decrease while k2o increases at any pressure the melt compositions are more potassic than the water saturated granitic minima the h2o contents estimated by mass balance are in the range 2 5 5 6 wt these values are higher than those predicted by thermodynamic models modal compositions were estimated by mass balance calculations and by image processing of the sem photographs the positions of the 20 to 70 isotects curves of equal proportion of melt have been located in the pressure temperature space between 100 mpa and 1000 mpa with increasing pressure the isotects shift toward lower temperature between 100 and 200 mpa then bend back toward higher temperature the melting interval increases with pressure the difference in temperature between the 20 and the 70 isotects is 40 c at 100 mpa and 150 c at 800 mpa the position of the isotects is interpreted in terms of both the solubility of water in the melt and the nature of the reactions involved in the melting process a comparison with other partial melting experiments suggests that pelites are the most fertile source rocks above 800 mpa the difference in fertility between pelites and greywackes decreases with decreasing pressure a review of the glass compositions obtained in experimental studies demonstrates that partial melting of fertile rock types in the crust greywackes pelites or orthogneisses produces only peraluminous leucogranites more mafic granitic compositions such as the various types of calk alkaline rocks or mafic s type rocks have never been obtained during partial melting experiments thus only peraluminous leucogranites may correspond to liquids directly formed by partial melting of metasediments other types of granites involve other components or processes such as restite unmixing from the source region and or interaction with mafic mantle derived materials

the trace element compositions of s type granites evidence for disequilibrium melting and accessory phase entrainment in the source within individual plutons the trace element concentrations in s type granites generally increase with maficity total iron and magnesium content and expressed as atomic fe mg in this study the degree of variability in trace element concentration also expands markedly with the same parameter the strongly peraluminous high level s type granites of the peninsular pluton cape granite suite south africa are the product of biotite incongruent melting of a metasedimentary source near the base of the crust leucogranites within the suite represent close to pure melts from the anatectic source and more mafic varieties represent mixtures of melt and peritectic garnet and ilmenite trace elements such as rb ba sr and eu that are concentrated in reactant minerals in the melting process show considerable scatter within the granites this is interpreted to reflect compositional variation in the source in contrast elements such as lree zr and hf which are concentrated within refractory accessory phases zircon and monazite show well defined negative correlations with increasing sio2 and increase linearly with increasing maficity this is interpreted to reflect coupled co entrainment of accessory minerals and peritectic phases to the melt leucocratic rocks cannot have evolved from the more mafic compositions in the suite by a process of fractional crystallisation because in this case they would have inherited the zircon saturated character of this hypothetical earlier magma trace element behaviour of granites from the peninsular pluton has been modelled via both equilibrium and disequilibrium trace element melting in the disequilibrium case melts are modelled as leaving the source with variable proportions of entrained peritectic phases and accessory minerals but before the melt has dis solved any accessory minerals thus the trace element signature of the melt is largely inherited from the reactants in the melting reaction with no contribution from zircon and monazite dissolution in the equilibrium case melt leaves the source with entrained crystals after reaching zircon and monazite saturation a significant proportion of the rocks of the peninsular pluton have trace element concentrations below those predicted by zircon and monazite saturation in the case of the most leucocratic rocks all compositions are zircon undersaturated whilst the majority of the most mafic compositions are zircon oversaturated however in both cases zircon is commonly xenocrystic thus the leucocratic rocks represent close to pure melts which escaped their sources rapidly enough that some very closely match the trace element disequilibrium melting model applied in this study zircon dissolution rates allow the residency time for the melt in the source to be conservatively estimated at less than 500 years

conjugate hemisphere ionospheric response to the st patrick s day storms of 2013 and 2015 in the 100 e longitude sector the effects of the st patrick s day geomagnetic storms of 2013 and 2015 in the equatorial and low latitude regions of both hemispheres in the 100 e longitude sector is investigated and compared with the response in the indian sector at 77 e the data from a chain of ionosondes and gps global navigation satellite systems receivers at magnetic conjugate locations in the 100 e sector have been used the perturbation in the equatorial zonal electric field due to the prompt penetration of the magnetospheric convective under shielded electric field and the over shielding electric field gives rise to rapid fluctuations in the f2 layer parameters the direction of imf bz and disturbance electric field perturbations in the sunset sunrise period is found to play a crucial role in deciding the extent of prereversal enhancement which in turn affect the irregularity formation equatorial spread f in the equatorial region the northward southward imf bz in the sunset period inhibited supported the irregularity formation in 2015 2013 in the 100 e sector large height increase hmf2 during sunrise produced short duration irregularities during both the storms the westward disturbance electric field on 18 march inhibited the equatorial ionization anomaly causing negative positive storm effect in low latitude equatorial region the negative effect was amplified in low midlatitude by disturbed thermospheric composition which produced severe density total electron content depletion the longitudinal and hemispheric asymmetry of storm response is observed and attributed to electrodynamic and thermospheric differences

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

experimental deformation of partially molten westerly granite under fluid absent conditions with implications for the extraction of granitic magmas the mechanical behavior of partially molten westerly granite was investigated in the temperature range 800 1100 c 250 mpa confining pressure by means of constant strain rate creep and stress relaxation tests the only water in the samples came from the breakdown of hydrous phases biotite minor chlorite and muscovite and alteration products of feldspars thus the amount of melt was controlled by the test temperature and ranged from 3 at 800 c to 50 at 1100 c over that temperature range strength decreased from 500 mpa to less than 1 mpa and a preliminary constitutive flow law for the partially molten rock was obtained to allow extrapolation to low strain rates the comparative viscosity of the melt alone was estimated at 950 and 1000 c from the distance it could be made to penetrate into a porous sand under a known pressure gradient under all conditions deformation of the matrix of solid grains was by brittle fracture only samples containing up to 10 vol melt failed with the formation of a shear fault zone at higher melt fractions melt filled pores collapsed by shear enhanced compaction squeezing the melt into axial cracks above 40 vol melt unfractured solid grains were carried about passively in the flowing liquid there was no evidence of a rheologically critical melt percentage in this system by analogy with the uniaxial compaction of water saturated soils a simple model is erected to describe a two stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress shear enhanced compaction is inferred to drive melt into a network of melt filled veins whereupon porous flow through the high permeability vein network allows rapid drainage of melt to higher crustal levels

exhumation mechanisms of melt bearing ultrahigh pressure crustal rocks during collision of spontaneously moving plates a series of 2d petrological thermomechanical numerical experiments was conducted to i characterize the variability of exhumation mechanisms of ultrahigh pressure metamorphic uhpm rocks during collision of spontaneously moving plates and ii study the possible geodynamic effects of melting at ultrahigh pressure conditions for the exhumation of high temperature ultrahigh pressure metamorphic ht uhpm rocks to this end the models include fluid and melt induced weakening of rocks five distinct modes of exhumation of u hpm rocks associated with changes in several parameters in the models of plate collision and continent subduction are identified as follows vertical crustal extrusion large scale crustal stacking shallow crustal delamination trans lithospheric diapirism and channel flow the variation in exhumation mechanisms for u hpm rocks in numerical models of collision driven by spontaneously moving plates contrasts with the domination of the channel flow mode of exhumation in a majority of the published results from numerical models of collision that used a prescribed plate convergence velocity and or did not include fluid and melt induced weakening of rocks this difference in the range of exhumation mechanisms suggests that the prescribed convergence velocity condition and the neglect of fluid and melt related weakening effects in the earlier models may inhibit development of several important collisional processes found in our experiments such as slab breakoff vertical crustal extrusion large scale stacking shallow crustal delamination and relamination and eduction of the continental plate consequently the significance of channel flow for the exhumation of uhpm rocks may have been overstated based on the results of the earlier numerical experiments in addition the results from this study extend over a larger proportion of the high temperature range of p t conditions documented from uhpm rocks including those retrieved from ht uhpm rocks than the results of experiments from previous numerical models in particular the highest peak metamorphic temperatures up to 1000 degrees c are recorded in the case of the vertical crustal extrusion model in which subducted continental crust is subjected to a period of prolonged heating by asthenospheric mantle abutting the continental side of the vertically hanging slab nonetheless some extreme temperature conditions which have been suggested for the kokchetav and bohemian massifs perhaps up to 1100 1200 degrees c are still to be achieved in experiments using numerical models

from sediment to granite timescales of anatexis in the upper crust abstract granite formation is the culmination of a sequence of events initiated by prograde heating of the protolith and followed by formation of a grain boundary melt melt segregation into a vein network ascent of the melt through the network and finally crystallisation of the melt experimental constraints on the formation of a crustal melt from the incongruent melting of muscovite combined with geochemical studies of anatexis in the high himalaya allow the timescales required for each of these processes to be assessed discordant temperatures determined from monazite and zircon thermometry for himalayan anatectic granites indicate that at least for some intrusives the melt was undersaturated in lree implying that melts have probably been extracted in less than 10 ka experimental studies suggest that some himalayan melts are also undersaturated in zr implying segregation may have occurred within 100 years such short timescales confirm that deformation driven mechanisms are important in extracting these melts from their source the transport distances of himalayan granitic melts of 10 km may be achieved by the ascent of magma through dykes in about 1 day at such rates even the largest granite could theoretically be emplaced in 10 years crystallisation of himalayan melts involves much longer periods if emplaced as thin sheets 100 m wide a timescale of 500 years is required compared with 30 ka for single stage intrusion of the larger laccoliths for composite sheet complexes magma crystallisation rather than melt ascent comprises the rate determining step on the emplacement of the intrusion the overall timescales of melt segregation and emplacement for many orogenic granites are therefore less than 10 ka and possibly less than 1 ka in contrast the timescale required for prograde heating of the protolith is 1 ma since the melt production rate is determined by heat flow into the protolith and not by reaction kinetics for any geologically significant period we conclude that heat flow determined by both the mechanism of heating and the thermal diffusivities of crustal rocks provides the overall rate determining step of crustal anatexis

on 226ra and 222rn concentrations in the brackish waters of coastal aquifers lab investigations and confirmation in the carbonate aquifer of brindisi italy the ground waters circulating in the apulian mesozoic carbonate aquifer of coastal type show high concentrations of 222rn everywhere considering their variation during the different phases of a hydrological year such high concentration values can reach activity of 20 bq l in the more internal zones of the aquifer moreover it is often observed that in correspondence of wells and springs nearest the coast the concentrations of radioactive gas reach values greater than 400 bq l and vary considerably during the course of a day and with withdrawals the research carried out over the last few years has confirmed that 226ra and 222rn concentrations in the karst groundwater of apulia are mainly related to the occurrence of terra rossa inside the aquifer and the capacity of these paleosols to fix the salts of 226ra coming from the dissolution of the calcareous and calcareous dolomitic rocks this paper shows the results of the analysis performed to define 222rn increase in the brackish waters that come in contact with carbonate rocks and terra rossa it also indicates the results of surveys performed in a coastal zone with well known hydrogeological features the controls performed during one hydrological year have confirmed the relationships between the salt content of the ground waters and the enrichment of 222rn and have highlighted that the manner of increase of this radioisotope is related to cases of ionic exchange and adsorption regulated by the dynamics of marine intrusion

dehydration melting of tonalites part ii composition of melts and solids dehydration melting of tonalitic compositions phlogopite or biotite plagioclase quartz assemblages is investigated within a temperature range of 700 1000 c and pressure range of 2 15 kbar the solid reaction products in the case of the phlogopite plagioclase an45 quartz starting material are enstatite clinopyroxene and potassium feldspar with amphiboles occurring occasionally at 12 kbar zoisite is observed below 800 c and garnet at 900 c the reaction products of dehydration melting of the biotite ann50 plagioclase an45 quartz assemblage are melt orthopyroxene clinopyroxene amphibole and potassium feldspar at pressures 8 kbar and temperatures below 800 c epidote is also formed almandine rich garnet appears above 10 kbar at temperatures 750 c the composition of melts is granitic to granodioritic hence showing the importance of dehydration melting of tonalites for the formation of granitic melts and granulitic restites at pressure temperature conditions within the continental crust the melt compositions plot close to the cotectic line dividing the liquidus surfaces between quartz and potassium feldspar in the haplogranite system at 5 kbar and ah2o 1 the composition of the melts changes with the composition of the starting material temperature and pressure with increasing temperature the melt becomes enriched in al2o3 and feo mgo potash in the melt is highest just when biotite disappears the amount of cao decreases up to 900 c at 5 kbar whereas at higher temperatures it increases as amphibole clinopyroxene and more an component dissolve in the melt the na2o content of the melt increases slightly with increase in temperature the composition of the melt at temperatures 900 c approaches that of the starting assemblage the melt fraction varies with composition and proportion of hydrous phases in the starting composition as well as temperature and pressure with increasing modal biotite from 20 to 30 wt the melt proportion increases from 19 8 to 22 3 vol 850 c and 5 kbar with increasing temperature from 800 to 950 c at 5 kbar the increase in melt fraction is from 11 to 25 8 vol the effect of pressure on the melt fraction is observed to be relatively small and the melt proportion in the same assemblage decreases at 850 c from 19 8 vol at 5 kbar to 15 3 vol at 15 kbar selected experiments were reversed at 2 and 5 kbar to demonstrate that near equilibrium compositions were obtained in runs of longer duration

ostwald ripening as a possible mechanism for zircon overgrowth formation during anatexis theoretical constraints a numerical model and its application to pelitic migmatites of the tickalara metamorphics northwestern australia a fundamental dichotomy exists between the low solubility of zircon in peraluminous melt predicted by experimental and geochemical studies and the large volume proportions of zircon overgrowths formed during high temperature metamorphism and anatexis that are revealed by cathodoluminescence imaging we investigate the potential of ostwald ripening as a possible mechanism for overgrowth formation by presenting a numerical solution to the continuity equation governing open system diffusion rate limited ostwald ripening in a zircon saturated melt application of the model to a typical log normal initial zircon crystal size distribution csd suggests that despite uncertainties associated with the interfacial free energy of zircon significant grain coarsening is possible via this mechanism under geological conditions and time scales relevant to high grade metamorphism primary influences on the rate at which ostwald ripening proceeds are i the temperature of the system ii the duration of the time interval for which the system is above its solidus and iii the nature of the initial premelting zircon csd to test the viability of the model we examine zircon csds from three high grade pelitic migmatites of the tickalara metamorphics northwestern australia assuming that zircon crystals hosted by melanosome biotite were permanently occluded from the melt and therefore approximate the premelting csd the model predicts that within 1 to 2 ma these biotite hosted zircon csds will evolve into the observed leucosome hosted zircon csds via melt present ostwald ripening under geological conditions applicable to peak metamorphism although we have not conclusively demonstrated that ostwald ripening contributed to changes in zircon csds during anatexis of the tickalara metapelites our results suggest that ostwald ripening is a viable mechanism for zircon volume transfer in a zircon saturated melt and capable of playing a significant role in overgrowth formation in rocks where the total volume of zircon overgrowths substantially exceeds the concentration of zircon dissolvable in the coexisting melt

long duration penetration of the interplanetary electric field to the low latitude ionosphere during the main phase of magnetic storms 1 it is well known that the interplanetary electric field can penetrate to the low latitude ionosphere it is generally believed that the penetration of electric fields can last only for 30 min because of the shielding effect in the ring current in this paper we present the observations of the dayside ionospheric electric field enhancements at middle and low latitudes in association with reorientations of the interplanetary magnetic field imf in six cases the eastward electric field in the dayside equatorial ionosphere measured by the jicamarca incoherent scatter radar was enhanced for 2 3 hours after the imf turned southward and remained continuously southward in one case the eastward electric field in the dayside midlatitude ionosphere measured by the millstone hill incoherent scatter radar was continuously enhanced for 10 hours during southward imf since millstone hill is close to the equatorward boundary of the auroral zone during magnetic storms the penetration electric field there may be different from that at the equatorial ionosphere the most striking feature of the measurements is that the enhancements of the ionospheric electric field can last for many hours without significant decay the electric field enhancements in the middle and low latitude ionosphere are closely related to magnetic activity and occur during the main phase of magnetic storms the observations show that the interplanetary electric field can continuously penetrate to the low latitude ionosphere without shielding for many hours as long as the strengthening of the magnetic activity is going on under storm conditions

duskside enhancement of equatorial zonal electric field response to convection electric fields during the st patrick s day storm on 17 march 2015 the equatorial zonal electric field responses to prompt penetration of eastward convection electric fields ppef were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 march 2015 at dusk sector indian longitudes a rapid uplift of equatorial f layer to 550 km and development of intense equatorial plasma bubbles epbs were observed these epbs were found to extend up to 27 13 n and 25 98 s magnetic dip latitudes indicating their altitude development to 1670 km at apex in contrast at few degrees east in the premidnight sector thailand indonesian longitudes no significant height rise and or epb activity has been observed the eastward electric field perturbations due to ppef are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo idd fields whereas they were mostly counter balanced by the idd fields in the premidnight sector in situ observations from swarm a and swarm c and communication navigation outage forecasting system satellites detected a large plasma density depletion near indian equatorial region due to large electrodynamic uplift of f layer to higher than satellite altitudes further this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator this study brings out the significantly enhanced equatorial zonal electric field in response to ppef that is uniquely confined to dusk sector the responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field bz

melt segregation in the continental crust before melt will segregate from its restite and source there must be both a driving force and space into which the melt can move the continental crust is anisotropic and in most cases is subject to deviatoric stresses during melting under these conditions melt segregation begins when an interconnected network of melt forms and the source becomes permeable melt is driven by pressure gradients from its restite toward dilatant sites set up in the heterogeneously deforming source the source is continually drained of melt and so need never contain more melt than that required to maintain permeability 26 where the solid matrix breaks down and diapirism can occur

multiple zircon growth during fast exhumation of diamondiferous deeply subducted continental crust kokchetav massif kazakhstan diamondiferous rocks from the kokchetav massif kazakhstan represent deeply subducted continental crust in order to constrain the age of ultra high pressure uhp metamorphism and subsequent retrogression during exhumation zircons from diamondiferous gneisses and metacarbonates have been investigated by a combined petrological and isotopic study four different zircon domains were distinguished on the basis of transmitted light microscopy cathodoluminescence trace element contents and mineral inclusions mineral inclusions and trace element characteristics of the zircon domains permit us to relate zircon growth to metamorphic conditions domain 1 consists of rounded cores and lacks evidence of uhp metamorphism domain 2 contains diamond coesite omphacite and titanian phengite inclusions providing evidence that it formed at uhp metamorphic conditions p 43 kbar t 950 c domain 3 is characterised by low pressure mineral inclusions such as garnet biotite and plagioclase which are common minerals in the granulite facies overprint of the gneisses p 10 kbar t 800 c this multi stage zircon growth during cooling and exhumation of the diamondiferous rocks can be best explained by zircon growth from zr saturated partial melts present in the gneisses domain 4 forms idiomorphic overgrowths and the rare earth element pattern indicates that it formed without coexisting garnet most probably at amphibolite facies conditions p 5 kbar t 600 c the metamorphic zircon domains were dated by shrimp ion microprobe and yielded ages of 527 5 528 8 and 526 5 ma for domains 2 3 and 4 respectively these indistinguishable ages provide evidence for a fast exhumation beyond the resolution of shrimp dating the mean age of all zircons formed between uhp metamorphic conditions and granulite facies metamorphism is 528 3 ma indicating that decompression took place in less than 6 ma hence the deeply subducted continental crust was exhumed from mantle depth to the base of the crust at rates higher than 1 8 cm year we propose a two stage exhumation model to explain the obtained p t t path fast exhumation on top of the subducted slab from depth 140 to 35 km was driven by buoyancy and facilitated by the presence of partial melts a period of near isobaric cooling was followed by a second decompression event probably related to extension in a late stage of continental collision

calculation of partial melting equilibria in the system na2o cao k2o feo mgo al2o3 sio2 h2o nckfmash a thermodynamic model for haplogranitic melts in the system na2o cao k2o al2o3 sio2 h2o nckash is extended by the addition of feo and mgo with the data for the additional end members of the liquid incorporated in the holland powell 1998 internally consistent thermodynamic dataset the resulting dataset with the software thermocalc is then used to calculate melting relationships for metapelitic rock compositions the main forms for this are p t and t x pseudosections calculated for particular rock compositions and composition ranges the relationships in these full system pseudosections are controlled by the low variance equilibria in subsystems of nckfmash in particular the solidus relationships are controlled by the solidus relationships in nkash and the ferromagnesian mineral relationships are controlled by those in kfmash however calculations in nckfmash allow the relationships between the common metapelitic minerals and silicate melt to be determined in particular the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks particularly relating to open system behaviour of rocks under high grade conditions

deep subduction and rapid exhumation role of crustal strength and strain weakening in continental subduction and ultrahigh pressure rock exhumation 1 the exhumation of crustal ultra high pressure uhp material depends on temporal and spatial variations in its detachment within the subduction channel this dependence is investigated using numerical models with variable initial crustal strengths representing a range of initial crustal compositions and parameterized strain weakening representing a range of processes that reduce effective crustal viscosity during deformation competition between down channel shear traction favoring subduction and up channel buoyancy favoring exhumation is expressed as the exhumation number e which can vary with time and position along the channel exhumed lower strength crust which resists subduction owing to weak down channel traction records peak conditions 38 kbar given sufficient strain weakening exhumation proceeds at 60 km ma 1 indicating that buoyancy e 1 drives exhumation in these models in all models exhuming uhp material forms a deforming ductile plume with a range of possible structural relationships predicted between exhumed uhp and hp materials

high fluxes of radium and barium from the mouth of the ganges brahmaputra river during low river discharge suggest a large groundwater source the annual flux of sediment from the ganges brahmaputra river is among the highest in the world the desorption of226ra and ba from this sediment produces a major point source of226ra and ba input to the ocean highest226ra and ba fluxes are expected to occur during high river flow june september when most of the sediment is discharged surprisingly during low discharge of the ganges brahmaputra river fluxes of226ra and ba to the northern bay of bengal are comparable to expected river derived fluxes during peak river discharge a large non riverine source of ra and ba is required to explain the high fluxes during low river discharge i suggest that this source is submarine discharge of groundwater containing high concentrations of226ra and ba total annual fluxes of226ra and ba to the ocean from this system are significantly greater than estimated previously

thermobarometric modelling of zircon and monazite growth in melt bearing systems examples using model metapelitic and metapsammitic granulites u pb age data collected from zircon and monazite are used to draw fundamental inferences about tectonic processes in the earth despite the emphasis placed on zircon and monazite ages the understanding of how to relate the timing of growth of zircon and monazite to an evolving rock system remains in its infancy in addition few studies have presented large datasets of geochronological data from zircon and monazite occurring in the same metamorphic rock sample such information is crucial for understanding the growth of zircon relative to monazite in a systematic and predictive manner as per this study the data that exist support the generally held conception that zircon ages tend to be older than monazite ages within the same rock here experimental data for zircon and monazite saturation in melt bearing rocks are integrated with phase diagram calculations the calculations constrain the dissolution and growth behaviour of zircon and monazite with respect to evolving pressure temperature and silicate mineral assemblages in high grade melt bearing metasedimentary rocks several key results emerge from this modelling first that in aluminous metapelitic rocks i e garnet cordierite sillimanite assemblages zircon ages are older than monazite ages in the same rock second that the growth rate of accessory minerals is nonlinear and much higher at and near saturation than at lower temperatures and third that the difference in zircon and monazite ages from the same rock may be ascribed to differences in the temperature s at which zircon and monazite grow rather than differences in closure temperature systematics using our methodology the cooling rate of granulites from the reynolds range central australia have been constrained at 4 c myr 1 this study serves as a first pass template on which further research in applying the technique to a field study can be based

crustal rheology of the himalaya and southern tibet inferred from magnetotelluric data the collision between the indian and asian continents which began about 70 million years ago involved a convergence of at least 1 400 km and raised the tibetan plateau since crustal material is too buoyant to be transported downwards into the earth s interior the mechanisms at work in plateau formation are important in understanding the evolution of the continents yet still a matter of debate geophysical observations in the himalaya and tibet using ultra low frequency radio waves now reveal that a partially molten layer is present along the entire length of the himalaya this weak layer implies that widespread crustal flow is occurring and explains many features of plateau evolution the cenozoic collision between the indian and asian continents formed the tibetan plateau beginning about 70 million years ago since this time at least 1 400 km of convergence has been accommodated1 by a combination of underthrusting of indian2 and asian lithosphere crustal shortening3 horizontal extrusion4 and lithospheric delamination5 rocks exposed in the himalaya show evidence of crustal melting1 6 and are thought to have been exhumed by rapid erosion and climatically forced crustal flow7 8 magnetotelluric data can be used to image subsurface electrical resistivity a parameter sensitive to the presence of interconnected fluids in the host rock matrix even at low volume fractions here we present magnetotelluric data from the tibetan himalayan orogen from 77 e to 92 e which show that low resistivity interpreted as a partially molten layer is present along at least 1 000 km of the southern margin of the tibetan plateau the inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in southern tibet

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

phase equilibria of the lyngdal granodiorite norway implications for the origin of metaluminous ferroan granitoids the proterozoic 950 ma lyngdal granodiorite of southern norway belongs to a series of hornblende biotite metaluminous ferroan granitoids hbg suite coeval with the post collisional rogaland anorthosite mangerite charnockite amc suite this granitoid massif shares many geochemical characteristics with rapakivi granitoids yet granodiorites dominate over granites to constrain both crystallization p t fo2 h 2o in melt and magma generation conditions we performed crystallization experiments on two samples of the lyngdal granodiorite with 60 and 65 wt sio2 at 4 2 kbar mainly at fo2 of nno nickel nickel oxide to nno 1 and under fluid saturated conditions with various h2o co2 ratios for each temperature comparison between experimental phase equilibria and the mineral assemblage in the lyngdal granodiorite indicates that it crystallized between 4 and 2 kbar from a magma with 5 6 wt h2 oa t an fo2 of nno to nno 1 these oxidized and wet conditions sharply contrast with the dry and reduced conditions inferred for the petrogenesis of the amc suite and many other rapakivi granites worldwide the high liquidus temperature and h2o content of the lyngdal granodiorite imply that it is not a primary magma produced by the partial melting of the crust but is derived by the fractionation of a mafic magma lyngdal type magmas appear to have volcanic equivalents in the geological record in particular our results show that oxidized high silica rhyolites such as the bishop tuff could be derived via fractionation of oxidized intermediate magmas and do not necessarily represent primary crustal melts this study underlines the great variability of crystallization conditions from anhydrous to hydrous and reduced to oxidized and petrogenetic processes among the metaluminous ferroan magmas of intermediate compositions granodiorites quartz mangerites quartz latites suggesting that there is not a single model to explain these rocks

transient hot channels perpetrating and regurgitating ultrahigh pressure high temperature crust mantle associations in collision belts abstract two dimensional numerical modeling of early continental collision associated with subduction of the lithospheric mantle shows that the formation and exhumation of coesite and diamond bearing rocks metamorphosed at 700 to 900 c in the presence of dense supercritical silicate fluids and melts may be explained by a transient hot channel effect anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper crustal rocks especially sediments of passive margin origin and mantle rocks heating is associated with partial melting of crustal rocks caused by pervasive flow of aqueous fluids relieved by rapid dehydration deserpentinization of the overriding mantle lithosphere that has been hydrated during earlier subduction stages the channel penetrates the plate interface to the bottom of the lithosphere of the overriding plate 150 200 km and is characterized by metamorphic temperatures reaching 700 to 900 c low effective viscosity of rocks subsequent to increased temperature partial melting and fluid infiltration permits profound mixing of hydrated mantle and crustal rocks the hot channel exists only during early collision but rapidly produces large amounts of ultrahigh pressure high temperature rocks further collision closes the channel by squeezing rheologically weak partially molten buoyant rocks between the strong lithospheric mantles of the two colliding plates assemblages of complicated p t paths with repetitive loops characterize exhumation of ultrahigh pressure rocks in the convoluted flow pattern of the hot channel

natural radioactivity of some red mediterranean soils abstract seventeen samples of b horizon of pleistocene terra rossa soils from carbonate rock were collected in different countries of the mediterranean regions spain italy and southern turkey the concentration of naturally occurring radionuclides 238 u 232 th k nat was measured in all samples using gamma ray spectrometry at the gran sasso national laboratory of infn italy the uranium content in terra rossa paleosols ranges from 1 to 5 ppm for thorium the concentration ranges from 3 ppm up to 30 ppm whereas for potassium it goes from 0 13 up to 1 3 the results indicated that soils characterised by absence or scarcity of 2 1 clay minerals are poor in uranium whereas soils with illite smectite as the dominant minerals in clay fraction are noticeably richer then it is suggested that uranium occurring in traces in the calcite lattice of carbonate rocks after it is the released by weathering migrates in solution as uo 2 2 and can be adsorbed by the soil exchange complex mainly by clay minerals of terra rossa soils

a simulation study of the equatorial ionospheric response to the october 2013 geomagnetic storm the ionospheric observation from ionosonde at sao luis 2 5 s 44 2 w 6 68 s dip latitude around the magnetic equator showed that the nighttime ionospheric f2 layer was uplifted by more than 150 km during the october 2013 geomagnetic storm the changes of the f2 peak height hmf2 at the magnetic equator were generally attributed to the variations of vertical drift associated with zonal electric fields in this paper the thermosphere ionosphere electrodynamics general circulation model tiegcm simulation results are utilized to explore the possible physical mechanisms responsible for the observed increase of hmf2 at sao luis the tiegcm generally reproduced the changes of f2 peak electron density nmf2 and its height hmf2 during the main and recovery phases of the october 2013 storm a series of controlled simulations revealed that storm time hmf2 changes at the magnetic equator are not purely associated with the changes of electric fields horizontal plasma transport due to meridional winds and thermospheric expansion also contributed significantly to the profound increase of nighttime hmf2 observed at sao luis on 2 october moreover the changes of meridional winds and neutral temperature in the equatorial region are associated with storm time travelling atmospheric disturbances originating from high latitudes

geochemistry and age of ultrahigh pressure metamorphic rocks from the kokchetav massif northern kazakhstan isotopic and geochemical data of the zerenda series metamorphic rocks from the kokchetav massif are reported some of these rocks contain microdiamond inclusions in garnets and other indicators of ultrahigh pressure metamorphism p 40 kbar t 900 1000 c the diamond bearing rocks exhibit distinctive geochemical characteristics compared to typical crustal rocks the ree patterns range from lree depleted to slightly lree enriched chondrite normalized la yb n 0 1 5 4 with a negative eu anomaly they are depleted in incompatible elements e g sr ba u th with respect to the upper crust in contrast non diamondiferous rocks of the zerenda series exhibit normal crustal geochemistry all rocks of the zerenda series have very radiogenic lead isotopes the measured values 238u 204pb compared with those calculated for the interval between crust formation and ultrahigh pressure uhp metamorphism suggest a decrease by factors of up to 200 during the uhp metamorphism the sm nd mineral isochrons from the diamond bearing rocks and other rock types of the zerenda series give a middle cambrian 524 535 ma age of metamorphism the nd model ages show that crust formation occurred about 2 3 ga ago significant fractionation of sm and nd and loss of incompatible elements may be due to partial melting of the protoliths the ar ar age determinations of secondary biotite and muscovite from the diamond bearing rocks yield an age of 517 5 ma this cooling age requires a short time interval between uhp metamorphism and uplift to a crustal level ultrahigh pressure metamorphism might be a significant source of pb for the mantle we propose that the radiogenic pb of the oceanic array is the contamination traces of numerous uhp events beside the geological aspect we demonstrate a method of dating a high grade metamorphic terrain using nd isotopes we compare whole rock isochrons and mineral isochrons and in this way get some insight into the behaviour of the sm nd system during very high grade metamorphic events

behavior of the f2 peak ionosphere over the south pacific at dusk during quiet summer conditions from cosmic data 1 the six satellite constellation observing system for meteorology ionosphere and climate cosmic mission makes routine ionospheric measurements over the entire globe using occultation techniques these observations have been used in this study to develop global scale climate maps of nmf2 and hmf2 during the southern northern summer winter enhanced electron densities that appear to be associated with the southern equatorial appleton anomaly are displaced far southward at dusk and within about an hour form the weddell sea anomaly coincidentally the height of the f2 peak increases on the northern boundary of this anomaly this height increase is also displaced southward as the enhanced electron densities are displaced southward suggesting that the electron density increases are associated with the f2 peak rising as well as being an interesting phenomenon in its own right this behavior may shed new light on the formation of the weddell sea anomaly no unambiguous explanation for this behavior can be determined from the data presently available but an examination of some possibilities suggests that an evening downward flux of plasma from the plasmasphere may be at least partly responsible for the phenomenon

rheology of some continental lower crustal rocks abstract to gain insight into the rheology of selected feldspar bearing rocks from the continental lower crust clc three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca 10 strain at confining pressures of 0 8 1 0 gpa temperatures of 600 900 c and constant strain rates of 10 4 10 7 s 1 the most extensive work was done on the mafic pikwitonei and felsic adirondack granulites the pikwitonei mg hornblende plag an70 2 px has only a limited t range of apparent steady state behavior and strain softens at t 800 c at 10 5 10 6s 1 apparently associated with developing shear zones this strain softening is pressure insensitive from pc 0 8 1 0 gpa at t 850 c 10 6s 1 even though the dominant strain accommodation mechanisms change from semibrittle cataclastic to crystal plastic including dynamic recrystallization with increasing pressure plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs kapuskasing plag cpx gt granulite deformed at 800 c and at 850 c 10 6 s 1 has deformed in the steady state at stress levels only slightly greater than the pikwitonei the stillwater microgabbro and adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady state behavior over the entire range of conditions investigated for the adirondack 2 felds 2 px gt qtz granulite quartz 21 appears to control the creep rate at these low strains and steady state mechanical data fit well a creep power law with a 8 10 3 mpa ns 1 qc 243 kj mol and n 3 1 extrapolation of this flow law and of preliminary power law creep relations for the pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone with the lower crust generally being the weaker material in addition the stain softening exhibited by the pikwitonei may bear directly on the development of detachment zones at mid to lower crustal depths during prograde metamorphism

effects of disturbed electric fields in the low latitude and equatorial ionosphere during the 2015 st patrick s day storm the 2015 st patrick s day geomagnetic storm with sym h value of 233 nt is an extreme space weather event in the current 24th solar cycle in this work we investigated the main mechanisms of the profound ionospheric disturbances over equatorial and low latitudes in the asian australian sector and the american sector during this super storm event the results reveal that the disturbed electric fields which comprise penetration electric fields pefs and disturbance dynamo electric fields ddefs play a decisive role in the ionospheric storm effects in low latitude and equatorial regions pefs occur on march 17 in both the american sector and the asian australian sector the effects of ddefs are also remarkable in the two longitudinal sectors both the ddefs and pefs show the notable local time dependence which causes the sector differences in the characteristics of the disturbed electric fields this differences would further lead to the sector differences in the low latitude ionospheric response during this storm the negative storm effects caused by the long duration ddefs are intense over the asian australian sector while the repeated elevations of hmf2 and the eia intensifications caused by the multiple strong pefs are more distinctive over the american sector especially the storm time f3 layer features are caught on march 17 in the american equatorial region proving the effects of the multiple strong eastward pefs

water fluxed melting of the continental crust a review abstract water fluxed melting also known as fluid or water present melting is a fundamental process in the differentiation of continents but its importance has been underestimated in the past 20 years during which research efforts focused mostly on dehydration melting reactions involving hydrate phases in the absence of a separate aqueous phase the presence of a free aqueous phase in anatectic terranes influences all major physical and chemical aspects of the melting process from melt volumes viscosity and ability to segregate from rock pores to melt chemical and isotopic composition a review of the literature shows that melting due to the fluxing of aqueous fluids is a widespread process that can take place in diverse tectonic environments active tectono magmatic processes create conditions for the release of aqueous fluids and deformation driven transient high permeability channels capable of fluxing high temperature regions of the crust where they trigger voluminous melting water fluxed melting can be either congruent in regions at the water saturated solidus or incongruent at suprasolidus p t conditions incongruent melting reactions can give rise to peritectic hornblende or to nominally anhydrous minerals such as garnet sillimanite or orthopyroxene in this case the presence of an aqueous phase is indicated by a mismatch between the large melt fraction generated and the much smaller fractions predicted in its absence the relatively small volumes of aqueous fluids compared to that of rocks imply that melting reactions are generally rock buffered fluids tend to move upwards and down temperature however there are cases in which pressure gradients drive fluids up temperature potentially fluxing suprasolidus terranes crustal regions at conditions equivalent to the water saturated solidus represent a natural impediment to the up temperature migration of aqueous fluids because they are consumed in melting reactions in this case continued migration into supra solidus terranes take place through the migration of water rich melts thus melts become the transport agent of water into supra solidus terranes and responsible for water fluxed melting other processes such as the relatively rapid fluid migration through fractures also allow regional aqueous fluids to by pass the water saturated solidus fluid trap and trigger melting above solidus conditions when aqueous fluids or hydrous melts flux rocks at supra solidus conditions they equilibrate with the surroundings through further melting decreasing water activity and giving rise to undersaturated melts it is in these conditions that hornblende or anhydrous peritectic phases are stabilized unlike dehydration melting the melt fraction generated in this case is not limited by the water contained in hydrous minerals but by the volume of water added to the system unlike melting at the water saturated solidus these melts are capable of rising without freezing and do give rise to upper crustal granitic bodies

observations of ion neutral coupling associated with strong electrodynamic disturbances during the 2015 st patrick s day storm we use incoherent scatter radar observations at millstone hill mho and arecibo ao and topside ionosphere in situ dmsp observations during the great geomagnetic storm on 17 18 march 2015 to conduct a focused study on ion neutral coupling and storm time ionosphere and thermosphere dynamics some of these observations were made around the time of large ionospheric drifts within a sub auroral polarization stream saps during the storm main phase we identify multiple disturbance characteristics in the north american late afternoon and dusk sector 1 strong sub auroral westward drifts occurred between 20 24 ut near mho accompanied by a storm enhanced density plume passage over mho in the afternoon with a poleward upward ion drift the strongly westward flow reached 2000 m s speed near the poleward plume edge 2 prompt penetration electric field signatures appearing as poleward upward ion drifts on the dayside over both mho and ao were consistent with dmsp vertical drift data and contributed to plume development 3 meridional wind equatorward surges occurred during daytime hours at mho followed by 2 3 hr period oscillations at both mho and ao the zonal electric field at ao was strongly correlated with the wind oscillation 4 large ion temperature enhancements as well as 50 m s upward ion drifts throughout the e and f regions were observed during the saps period these were presumably caused by strong frictional heating due to large plasma drifts the heating effects appeared to drive significant atmospheric upwelling and corresponding ion upflow was also observed briefly this study highlights some of the important effects of fast plasma transport as well as other disturbance dynamics on ion neutral coupling during a single intensification period within a great geomagnetic storm

fluids p t paths and the fates of anatectic melts in the earth s crust this paper presents a model for the longevity and physical behaviour of anatectic melts in the earth s crust it is assumed that a thermal anomaly has caused partial fusion of biotite plagioclase quartz rocks to produce a granitic melt and restitic solids the focus is on the potential chemical and physical outcomes as a function of the various p t fluid conditions rocks undergoing fluid present melting will sustain an increase in bulk density and will become more gravitationally stable diapiric up welling of such material should not occur in fluid absent melting the bulk density will decrease and foster gravitational instability stresses in the surrounding rocks could however lead to fracture and rapid evacuation of the melt with excess fluid and without melt segregation isobaric cooling will cause immediate freezing if t rises above the biotite quartz melting reaction freezing will still occur at the original reaction t diapiric up welling should not occur biotite bearing diatexites might be formed by large degrees of fusion but magma ascent is unlikely in isothermal decompression immediate freezing will ensue and the migmatite should contain orthopyroxene rather than biotite with excess fluid and melt segregation cooling will induce freezing at the fluid saturated granite solidus magma ascent could however occur even for xflh2o 1 in isothermal decompression melt will persist to the granite solidus for the imposed xflh2o limited magma ascent could occur all granites should contain primary igneous biotite for fluid deficient rocks without melt segregation freezing will occur at the t of the original melting if the reaction is overstepped solidification will occur at the original xflh2o magma formation is unlikely migmatites should contain either pyroxene retrogressed to biotite or biotite alone on decompression immediate freezing is likely if t remains at the biotite quartz reaction for higher t melt will survive decompression and freeze at the fluid saturated solidus for some increased xflh2o magma ascent is possible and the melt will freeze very close to the wet granite solidus in fluid deficient rocks with melt segregation cooling and crystallization will cause fluid saturation in situ segregated melt will freeze at the original xflh2o melt ascent will however cause exsolution of a co2 rich fluid with fluid escape melt will freeze close to the wet granite solidus an increase in melt proportion may accompany magma ascent or source up welling any low p granite intrusion should be charnockitic for fluid absent rocks without melt segregation freezing will occur on cooling to the t of the original reaction only transitory migmatites could be formed but melt will survive decompression almost to the h2o saturated granite solidus the rocks will reveal former melt presence only in the existence of veins of coarse retrograde biotite with isothermal decompression further melting may occur forming an orthopyroxene bearing granulite facies migmatite in fluid absent situations with melt segregation magma could be efficiently transported to higher crustal levels if the melt proportion were insufficient for magma formation granulite facies migmatites would result ascending melt would progressively dissolve any entrained restite the granites produced should be charnockitic to aid in interpretation of the modelling results we suggest that it may be slightly more common for the highest grade metamorphic terranes to exhibit isobaric cooling paths that fluid present anatexis is normally limited to the shallower parts of the crust and that fluid absent reactions are more likely at greater depths we conclude that the best models for natural fluid present anatexis are those dealing with essentially pure h2o fluid and that fluid deficient conditions will dominate over fluid excess we also believe that it is common for melts to be physically segregated on scales larger than the diffusion paths of many elements

thermomechanical modelling of slab detachment abstract slab detachment or breakoff is appreciated as an important geological process as shown by recent tomographic imaging using a 2 d upper mantle model 660 km deep and 2000 km wide we have investigated with a 2 d finite difference and marker in cell numerical technique the multi resolutional character of the thermomechanical phenomena related to this complex geological process our experiments show that this process can be initiated in form of slab necking by a prolonged 8 30 my period of slab weakening due to thermal diffusion 60 c my due to strong positive thermal feedback from shear heating detached slab fragments sink rapidly with a tendency for coherent rotation the influence of temperature and pressure dependent thermal conductivity on the process of thermal weakening of the slab is quite significant this supports the idea that the breakoff process is triggered by thermal diffusion on a time scale linearly dependent on heat conductivity rapid topographic changes and increasing volcanic activities due to the melting of subducted oceanic crust are possible scenarios of this vigorously driven geodynamic process

variation of the equatorial height anomaly during the main phase of 2015 st patrick s day geomagnetic storm using annim and tiegcm

inclusion host relations involving accessory minerals in high grade metamorphic and anatectic rocks in general accessory minerals are expected to participate in partial fusion of their host rocks to a degree determined simply by their solubilities in the melt the possibility must be recognized however that a given accessory grain may be physically isolated from the melt by inclusion within a residual major mineral because of the importance of accessory minerals to crustal rock trace element and isotope geochemistry and because of their common existence as inclusions in major phases we undertook an evaluation of the factors that affect inclusion formation during ultrametamorphism three approaches are taken 1 a review of interfacial energy considerations is used to show that the free energy of the system is lowered by location of accessory minerals at major phase grain perimeters and that the magnitude of this effect is proportional to the square of the accessory grain radius 2 annealing and partial melting experiments 1000 c 10 and 15 kbar on rock analogs are described and the results are shown to confirm the predicted tendency of accessory minerals to occupy grain boundaries and 3 the results of a study of accessory phase rutile and zircon distribution in a migmatite from the tibetan slab are reported again in confirmation of the prediction that accessories tend to be situated at majorphase grain perimeters the latter two aspects of the study reveal that although included accessory grains are common their generally small size results in only a minor contribution to the bulk rock budget of accessory mineral components most of the mass of these components is contained within populations of generally larger accessory grains located at major phase grain boundaries accordingly the assumption that accessory minerals are involved in crustal melting is generally valid

responses in the polar and equatorial ionosphere to the march 2015 st patrick day storm the st patrick day storm of 2015 17 march 2015 occurred at a unique time when there were multiple spacecraft observing the earth s ionosphere between 350 and 885 km observations of the plasma flows and densities from the five operational polar orbiting dmsp spacecraft combined with those from the equatorial orbiting c nofs spacecraft provided a comprehensive global record of the both the polar and equatorial ionosphere regions responses to the storm this paper presents an overview of the data from this suite of spacecraft focusing on the following aspects 1 the polar cap ionosphere s reaction to the storm 2 the change in the penetration electric field in the midlatitude region as a function of time and the solar local time during the storm 3 the equatorial ionosphere s response of the meridional vertical flows to the penetration electric field and the disturbance dynamo during the storm and 4 the creation of a predawn ionospheric bubble system near the equator during the storm s main phase that was observed at low altitudes by c nofs and later at high altitudes by several dmsp examining these phenomenon enable us to trace the dynamic flow of energy from the solar wind input in the polar ionosphere all the way to the equatorial ionosphere

electrodynamic disturbances in the brazilian equatorial and low latitude ionosphere on st patrick s day storm of 17 march 2015 the st patrick s day storm of 17th march 2015 has a long lasting main phase with the dst reaching a minimum of 223 nt during the main phase two strong prompt penetration electric field ppef phases took place first with the southward turning of imf bz around 1200 ut and the second with the onset of a substorm around 1725 ut leading to strong equatorial zonal electric field enhancements the consequent spatio temporal disturbances in the ionospheric total electron content tec and the resultant modifications in the equatorial ionization anomaly eia over the brazilian longitudinal sector are investigated in detail the simultaneous measurements from a large network of gps receivers ionosonde and magnetometers over the brazilian longitudinal sector are used for this study in the presence of enhanced zonal electric field the equatorial f2 layer peak hmf2 experienced a rapid uplift without any significant change in the base height h f while the f2 layer is redistributed into f2 and f3 layers the enhanced zonal electric filed due to ppef led to the strong super fountain effect under which the anomaly crest departed poleward to 40o s latitude in the presence of westward and equatorward wind surge over brazil with the co existing disturbance dynamo fields strong hemispheric asymmetry is seen in the storm time response of eia during both the ppef phases

a study of the weddell sea anomaly observed by formosat 3 cosmic 1 more than two years of cosmic electron density profiles at low solar activities are collected to study the evolution of the weddell sea anomaly wsa which appears as an evening enhancement in electron density during local summer observations show that the change in nmf2 the f2 peak electron density is associated with the change in hmf2 the f2 peak height while the latter is correlated closely with the components of the geomagnetic field we find that 1 in the afternoon hmf2 is more liable to rise drastically in regions with a larger jsin 2i j value which would occur early at certain declinations eastward in the southern hemisphere and westward in the northern hemisphere 2 subsequently a larger increment of hmf2 is coincidentally followed by a stronger enhancement of nmf2 and the enhancement ends just around the local sunset and 3 in midlatitudes the evolution pattern of hmf2 in the evening of equinoxes and winter is similar to that in summer albeit without a lasting nmf2 enhancement as that in summer these features suggest that the nmf2 enhancement and the hmf2 increase could arise from the thermospheric wind effect and solar photoionization plays a crucial role in the enhancement as well the general midlatitude f2 layer enhancement in local summer evening is consistent with the wsa on the above features indicating that the wsa is a manifestation with a particular geometry of the magnetic field of the evening enhancement induced by the winds

presence of palaeoproterozoic and archean components in the granulite facies rocks of central iberia the hf isotopic evidence abstract hf isotope analyses in previously dated zircon crystals from four variscan granulite facies rocks from central iberia have been studied to examine crustal evolution processes two samples are from exposed migmatite terranes the other two are granulite xenoliths from lower crustal levels hf model ages show that lower crustal granulites display a bigger contribution of archean components than exposed high grade rocks 14 of the zircon population instead of 6 reinforcing ideas of preservation of ancient crustal material in the lower crust the distribution of age hf isotope data from zircon suggests two juvenile crust formation events in central iberia the main one during the neoproterozoic 540 620 ma and a possible second mesoproterozoic event around 1 0 1 2 ga magmatism appears in the central iberian zone exclusively related to that younger juvenile addition hf data of granulite zircons agrees with recent palaeogeographical reconstruction models which present central iberia as a peri gondwanan terrane located between the west african craton and the arabian shield far from the amazonia microplate

fractionation of metaluminous a type granites an experimental study of the wangrah suite lachlan fold belt australia abstract crystallisation experiments were performed on two metaluminous a type granite compositions ab412 and ab422 from the wangrah suite a representative a type granite suite from the lachlan fold belt south eastern australia ab412 is more mafic than ab422 and zircon saturation temperatures are 897 and 843 c respectively experiments were performed at 200 mpa f o 2 between nno and nno 1 05 in a temperature range between 700 and 900 c for various melt h 2 o contents experimental results were compared to the natural phase compositions to constrain the water content of the melt and the phases involved in fractionation processes in the wangrah suite with decreasing temperature fe ti oxide orthopyroxene and plagioclase are the first phases to crystallise followed by biotite the orthopyroxene stability is mainly restricted to temperatures above 750 c hornblende is only stable in the less evolved composition if the water content of the melt is at least 4 5 wt h 2 o the initial water content in the more mafic melt ab412 was between 2 and 3 wt h 2 o although orthopyroxene is not observed in the natural assemblages of the wangrah suite it has influenced the early fractionation of the wangrah suite granites mass balance calculations show that composition ab422 can be obtained after the crystallisation of 4 7 wt iron rich orthopyroxene plus 8 5 wt plagioclase from ab412

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

observations and simulations of the ionospheric and thermospheric response to the december 2006 geomagnetic storm initial phase 1 we have investigated the thermospheric and ionospheric response to the 14 15 december 2006 geomagnetic storm using a coupled magnetosphere ionosphere thermosphere cmit 2 0 model simulation in this paper we focus on observations and simulations during the initial phase of the storm about 8 h when the shock was driving changes in geospace the global ionospheric maps of total electron content tec ionosonde data at four stations and millstone hill incoherent scatter radar isr observations are compared with the corresponding simulation results from the cmit model the observations showed significant positive storm effects occurred in the atlantic sector after the onset of this storm the cmit model is able to capture the temporal and spatial variations of the ionospheric storm effects seen in the gps tec observations although the model slightly underestimates the daytime positive ionospheric storm in the south american sector the simulations are also in agreement with the ionosonde and isr ionospheric measurements term analysis of the ion continuity equation demonstrates that changes in the electric fields play a dominant role in generating the observed ionospheric positive storm effect in the american sector during the initial phase although neutral winds and composition changes also contribute the difference in the strength of the enhancements over north and south america can be explained by the slope of the topside electron density profiles in the two hemispheres in the southern hemisphere electron densities decrease slowly with altitude whereas the decrease is much more rapid in the northern winter hemisphere the electric fields therefore cannot cause large increases in electron density by uplifting the plasma so positive storm effects are small in the southern hemisphere compared with the northern hemisphere even though the increase in hmf2 is greater in the southern hemisphere nighttime changes in electron density in other longitude sectors are small because the topside electron densities also decrease slowly with altitude at night

u pb dates and trace element geochemistry of zircon from migmatite western gneiss region norway significance for history of partial melting in continental subduction article i nfo thewesterngneissregion wgr norway isdominatedbymigmatiticgneissthatcontainsinclusionsofeclogite some of which contain evidence for ultrahigh pressure metamorphism to evaluate geochemical and age relation ships between host migmatite and eclogite we obtained la icp ms u pb dates and trace element analyses for zircon from a variety of textural types of leucosome from layer parallel to crosscutting zircon textures euhedral oscillatory and sector zone grains indicate a likely magmatic origin of the leucosomes caledonian u pb zircon dates from zircon rim and near rim regions are as old as 410 406 ma coeval with previously determined ages of high and ultrahigh pressure metamorphismof wgr eclogite trace elementanalysesobtained simultaneously with u pb dates indicate crystallization of zircon under garnet present conditions in the majority of leucosomes other zircons including those from crosscutting pegmatite yield younger ages as young as 385 ma coinciding with dates determined for amphibolite facies retrogression of eclogite trace element analyses suggest that these zircons grew under plagioclase present garnet absent conditions combined age and trace element data for leucosome zircons record the transition from high pressure garnet present plagioclase absent crys tallization to lower pressure plagioclase present crystallization if the euhedral zircons that yield ages coeval with peak or near peak uhp metamorphism represent crystallization from anatectic leucosomes these results combined with field and petrographic observations of eclogite migmatite relationships are consistent with the presence of partially molten crust in at least part of the wgr during continental subduction the decreased viscosity and increased buoyancy and strain weakening associated with partial melting may have assisted the rapid ascent of rocks from mantle to crustal depths

chemical and isotopic δ18o δ2h δ13c 222rn multi tracing for groundwater conceptual model of carbonate aquifer gran sasso infn underground laboratory central italy summary a hydrochemical and isotope study was conducted on the drainage waters of an underground laboratory located inside the gran sasso massif central italy the study was expected to improve the conceptual model of groundwater circulation at the base of an over 1000 thick unsaturated zone in the gran sasso partitioned karst aquifer this lithostratigraphically and tectonically complex aquifer is typical of africa europe thrust and fold collision belt in the mediterranean area in this case investigations on water rock interactions during recharge in complex aquifers overlaid by a thick unsaturated zone have been made thanks to the strategic location of the gran sasso underground laboratories located in the core of a huge carbonate aquifer knowledge of the local basic hydrogeological setting was the starting point for a detailed hydrogeochemical and isotopic study which was carried out at the aquifer scale and at the fine scale in the underground laboratories the water rock interaction processes were investigated both spatially and in temporal sequences analysing recharge waters and groundwater in the underground laboratories by multitracing techniques including major ions and 18o 2h and 13c stable isotopes use of 222rn provides information on transit time in the aquifer processes proved to be typical of carbonate rocks with clear influence of vertical movement of water on chemical physical parameters through the unsaturated zone conversely in the saturated zone these processes proved to be dominantly affected by local geological structural conditions a conceptual model with dual flow velocity is proposed directly related to the local geological structural setting 222rn decay enables to calculate an effective velocity of around 10 m day for the fracture network through the sequence of less permeable dolomites and underlying limestone lag time between recharge and chemical changes in the saturated zone testifies to an effective velocity of about 35 m day for fast flow through recent and active extensional faults

quantifying frozen melt in crustal rocks a new melt o meter based on zircon rim volumes abstract quantifying the distribution of granitic melt at all scales in mid to lower crustal migmatitic terranes is critical to understand crustal melting processes chemical differentiation of the crust and its rheological behavior during deformation we propose a new method to determine the fraction of frozen granitic melt on a hand specimen scale based on the relative volumes of newly precipitated to total zircon fpz fraction of newly precipitated zircon as obtained by image analysis on dated zircon cores and rims using the calculated zr solubility zr sat in the melt at the inferred melting temperature and the zr concentration in the bulk sample zr bulk the fraction of melt fmelt can be determined through fmelt fpz zr bulk zr sat the such obtained fmelt corresponds to the melt fraction in the hand specimen at the time the system closed for melt mobility thermodynamic modelling further allows estimation of h2o contents required to maintain the melt fraction obtained from the melt o meter in a molten stage the applicability of this method has been tested on eight migmatitic samples with peak temperatures between 725 and 925 c most of the lower temperature migmatites 800 c retained fmelt of 0 35 0 50 0 07 0 10 at these melt fractions melt extraction and melt migration from and within the source should be efficient consequently these samples are likely open system migmatites affected by melt accumulation or depletion processes the melt o meter requires that the rock types under consideration produced a granitic melt that remained zircon saturated and is therefore restricted to migmatitic meta sediments and meta granitoids when applied carefully this melt o meter offers a new and powerful tool to not only quantify melt distribution but also evaluate the extent of melt mobility in migmatites

penetration of magnetospheric electric fields to the equator during a geomagnetic storm 1 penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 november 2001 by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator yap 0 3 gml and low latitude okinawa 14 47 gml the penetrated electric field caused the dp2 currents at the equator i e eastward currents during the main phase of the storm while the overshielding currents i e westward currents dominated during the recovery phase it is shown that the ring current started to develop simultaneously with the onset of the equatorial dp2 within the temporal resolution of a few minutes these results imply prompt transmission of the dawn to dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere it is found that the equatorial dp2 started to decrease one hour after the onset of the ring current development indicating shielding effects becoming effective at the equator during the latter half of the storm main phase the dp2 was then overwhelmed by the overshielding which resulted in the counter electrojet cej in the beginning of the storm recovery phase the image magnetometer chain data indicate that the westward auroral electrojet aej in the dawn sector was driven over midlatitude centered at 57 corrected geomagnetic latitude cgml during the main phase while the aej shifted rapidly poleward to the auroral latitude centered at 67 cgml in the beginning of the recovery phase the overshielding must be caused by the abrupt poleward shift of the rl facs as inferred from the poleward shift of the aej in addition to the decrease in their magnitude due to the decrease in magnitude of the southward imf the geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2 7 as compared with the geomagnetic storm at low latitude this amplification is a result of both effects of the dp2 currents and the cej associated with the main and recovery phases respectively it is suggested that the electric field associated with the dp2 currents contributed to the development of the ring current during the main phase while the overshielding electric field may contribute to cease developing the ring current during the recovery phase

dynamics of slab detachment 1 we investigate the dynamics of slab detachment around the detachment zone and evaluate the amount of time necessary for slabs to detach the study combines results of two dimensional 2d state of the art thermomechanical numerical simulations and a 1d analytical solution for viscous necking under gravity we show that the dominant deformation mechanism during slab detachment is viscous necking independent of the depth of slab detachment when the slab dip is moderate 35 70 slab detachment is partly affected by localized simple shearing in the colder parts of the slab brittle fracturing breaking plays a minor role during slab detachment our 2d thermomechanical models indicate that the duration of slab detachment quantified from the onset of slab thinning until the actual detachment i e vanishing of slab pull force is relatively short 250 km can occur within a short time interval 1 ma which has implications for geodynamic interpretations using slab detachment as explanation for processes such as melting exhumation or surface uplift the thinning of the slab during detachment observed in 2d simulations agrees well with predictions from a 1d analytical solution indicating that the 1d solution captures the first order features of the detachment process we also evaluate the impact of shear heating on the duration of slab detachment the predictions of a simple semi analytical solution based on dimensionless parameters agree well with our and previously published results

styles of post subduction collisional orogeny influence of convergence velocity crustal rheology and radiogenic heat production abstract a number of models of continental collision already exist but the role of foregoing oceanic plate subduction or variable coupling between plates still remains to be explored in addition heat generation by radioactive decay may be quite variable for example our geochemical data from low to high grade metamorphic rocks of the lesser and higher himalayan sequences reveal measured heat production values on the order 4 5 w m 3 which is considerably higher than normal inferred upper crustal values 3 therefore we performed 2d numerical experiments of oceanic continental subduction followed by continental collision for varying continental lower crustal strength convergence velocity and radiogenic heating rate oceanic subduction produces thinning and upwarping of the overriding lithospheric wedge such as is observed in andean type collisional settings cascadia and central andes after collision two main orogenic styles develop depending on the values of key parameters either a slow convergence rates weak shear heating and consequently strong rheological coupling between plates and or a weak lower crust generate a two sided thick and narrow symmetrical collisional zone or b high convergence rates strong shear heating and therefore weak rheological coupling between plates and a strong lower crust produce a one sided thin and broad asymmetrical collisional zone in this case a vertical lithospheric body divides two upper crustal wedges that develop distinct deformation patterns in both cases enhanced radiogenic heating favors the formation of midcrustal partially melted channels that propagate toward the surface and the pro foreland partial melting triggers lateral extrusion of metamorphic rocks from different depths 15 23 kbar 700 c on top of coherent lp lt units the geometry of metamorphic isograds inverted shapes of p t paths at different grades and exhumation rates are similar to those observed in parts of the himalayan chain indicating that the models capture the essence of real systems the model results demonstrate that internal heat production rate is a crucial parameter in determining the timing of slab breakoff polarity reversal and exhumation of the inverted metamorphic sequence with respect to the timing of partial melting late stages of some numerical experiments showed interesting geodynamical evolution of the collisional zone with the appearance of polarity reversal roll over of both plates and roll back of the subducting slab irrespective of these details hundreds of km of continental lithosphere are recycled into the mantle in all models supporting the idea that continental crustal consumption is indeed a common and considerable process during collision this affects inferences about extents of convergence and or shortening during orogenesis moreover crustal recycling into the deep mantle during collisional orogeny needs to be considered in models of crustal growth and evolution

double crests of peak height in the equatorial ionospheric f2 layer observed by cosmic for the first time we report daytime double crests of peak height hmf2 in the f2 layer based on the constellation observing system for meteorology ionosphere and climate cosmic observations during 2007 2014 evident double crests of hmf2 occurred at around 10 geomagnetic latitude with a trough over the magnetic equator at low solar activity and at march equinox this phenomenon is referred to as an equatorial height anomaly eha of the ionospheric f2 layer the double crests became less obvious at september equinox and disappeared at solstices at solstices only one crest was observed in the summer hemisphere which is probably associated with transequatorial neutral winds in addition the double eha crests generally take place during 10 00 14 00 local times our results indicate that the eha favors the conditions of strong vertical plasma drifts and weak transequatorial neutral winds during low solar activity the eha feature is reproduced by the thermosphere ionosphere electrodynamics global circulation model at march equinox and low solar activity

phase relationships of s type granite with h2o to 35 kbar muscovite granite from harney peak south dakota muscovite granite 13 8 muscovite 4 8 normative corundum was reacted with varying percentages of h 2o in cold seal vessels at 2 kbar and in piston cylinder apparatus between 10 and 35 kbar the diagrams illustrating melting crystallization relationships are p t sections with both excess h 2o and with no h 2o added 0 66 h 2o in rock t x h 2o sections at 15 kbar and 25 kbar showing h 2o undersaturated conditions the h 2o undersaturated surface for the crystallization of quartz coesite small amounts of aluminosilicate minerals persist to higher temperatures glass compositions measured by electron microprobe from samples with 5 h 2o at 15 kbar confirm that liquids are syenitic through at least 100 c above the solidus as predicted from the effect of pressure on the residua system results are explained successfully by phase relationships involving muscovite quartz and orthoclase in k 2o al 2o 3 sio 2 h 2o with reactions depicted in a p total p e h 2o t model with special reference to the divariant surfaces in the region p e h 2o p total with reduced p e h 2o or a h 2o produced either by small amounts of h 2o and h 2o undersaturation or by co 2 h 2o mixtures subsolidus dehydration reaction temperatures decrease vapor present solidus temperatures increase and muscovite stability in presence of liquid increases in general muscovite biotite and amphibole can be precipitated from magmas containing only a few tenths per cent h 2o although the h 2o undersaturated liquids coexisting with crystals may contain 3 or more dissolved h 2o this particular granite cannot be a primary magma from mantle or subducted oceanic crust it is a possible product of partial fusion of pelitic rocks between about 20 km and 40 km depth given sufficient h2o and xenocrystal muscovite or sillimanite from the source rocks the phase relationships are consistent with the idea of s type granites but not sufficient to prove the origin of this rock additional tests require phase relationships of other associated granitic rocks and details of geochemistry geophysics and field relationships

three dimensional ionospheric electron density structure of the weddell sea anomaly 1 this paper provides the first three dimensional description of the ionospheric density structure of the weddell sea anomaly wsa the wsa is characterized by a nighttime ionospheric density greater than that in daytime in the weddell sea region around the antarctic peninsula during the southern hemisphere summer it was first observed by ground based ionosondes located in the antarctica back in the 1950s and was further investigated by two dimensional maps over the oceans using tec measurements collected by the topex poseidon recently although these tec maps have provided two dimensional views for tracking the time evolution and spatial coverage of the wsa the vertical distribution of this peculiar feature is still unavailable with the vertical ionospheric density profiles observed by the formosat 3 cosmic three dimensional density structure of the wsa is presented here for the first time meanwhile a similar wsa signature is observed in the northern and eastern hemisphere during june solstice by both the gps tec and the formosat 3 cosmic electron density observations from the observed altitudinal structure of the wsa during 1800 2400 lt and the similar feature occurred in the opposite hemisphere suggest that the southward offset of the magnetic equator with respect to the geographic equator plays a major role for the wsa formation

slow subduction of a thick ultrahigh pressure terrane 1 high precision lu hf and sm nd ages reported here cover a large portion of the western gneiss region wgr ultrahigh pressure uhp terrane norway and range from 413 9 3 7 to 397 1 4 8 ma collectively new and existing geochronologic data for eclogites demonstrate that eclogite facies metamorphism occurred over a large area 60 000 km2 for an unexpectedly long period of 20 ma a thermal model using slow subduction 2 4 mm a 1 of a relatively warm and thick slab can reproduce the observed p t t history of the wgr uhp terrane indicating that large uhp terranes with protracted peak or near peak histories probably reflect slow subduction of relatively thick crustal sections

behavior of zircon in the upper amphibolite to granulite facies schist migmatite transition ryoke metamorphic belt sw japan constraints from the melt inclusions in zircon behavior of zircon at the schist migmatite transition is investigated syn metamorphic overgrowth is rare in zircon in schists whereas zircon in migmatites has rims with low th u that give 90 3 2 2 ma u pb concordia age between inherited core and the metamorphic rim a thin dark cl annulus containing melt inclusion is commonly developed suggesting that it formed contemporaneous with the rim in the presence of melt in diatexites the annulus is further truncated by the brighter cl overgrowth suggesting the resorption and regrowth of the zircon after near peak metamorphism part of the zircon rim crystallized during the solidification of the melt in migmatites preservation of angular shaped inherited core of 5 10 m in zircon included in garnet suggests that zircon of this size did not experience resorption but developed overgrowths during near peak metamorphism the ostwald ripening process consuming zircon less than 5 10 m is required to form new overgrowths curved crystal size distribution pattern for fine grained zircons in a diatexite sample may indicate the contribution of this process zircon less than 20 m is confirmed to be an important sink of zr in metatexites and ca 35 m zircon without detrital core are common in diatexites supporting new nucleation of zircon in migmatites in the ryoke metamorphic belt at the aoyama area monazite from migmatites records the prograde growth age of 96 5 1 9 ma using the difference of growth timing of monazite and zircon the duration of metamorphism higher than the amphibolite facies grade is estimated to be ca 6 myr

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

geospace system responses to the st patrick s day storms in 2013 and 2015 this special collection includes 31 research papers investigating geospace system responses to the geomagnetic storms during the st patrick s days of 17 march 2013 and 2015 it covers observation data assimilation and modeling aspects of the storm time phenomena and their associated physical processes the ionosphere and thermosphere as well as their coupling to the magnetosphere are clearly the main subject areas addressed this collection provides a comprehensive picture of the geospace response to these two major storms we provide some highlights of these studies in six specific areas 1 global and magnetosphere plasmasphere perspectives 2 high latitude responses 3 subauroral and mid latitude processes 4 effects of prompt penetration electric fields and disturbance dynamo electric fields 5 effects of neutral dynamics and perturbation and 6 storm effects on plasma bubbles and irregularities we also discuss areas of future challenges and the ways to move forward in advancing our understanding of the geospace storm time behavior and space weather effects

low latitude ionospheric height variation as observed by meridional ionosonde chain formation of ionospheric ceiling over the magnetic equator a multipoint ionosonde observation campaign was conducted along the magnetic meridional plane in southeast asia to study ionosphere thermosphere coupling one station was near the magnetic equator and two of the other stations were at off equatorial latitudes 10 magnetic latitude the daytime ionospheric peak height hmf2 was analyzed for each season during the solar minimum years 2006 2007 and 2009 the peak height increased for 3 h after sunrise at the magnetic equator and off equatorial latitudes as expected from the daytime upward e b drift the apparent upward drift at the magnetic equator ceased before noon while the drift at the off equatorial latitudes continued upward and the layer height exceeded the equatorial height around noon the noontime limited layer peak height at the magnetic equator which was termed the ionospheric ceiling did not depend on the season while the maximum peak height at the off equatorial latitudes largely varied with each season numerical modeling using the sami2 code was conducted and the features of the ionospheric ceiling were reproduced quite well the dynamical parameters provided by the sami2 modeling runs showed that the ionospheric ceiling is formed by the field aligned plasma diffusion which is a part of the fountain effect

equatorial ionization anomaly in the low latitude topside ionosphere local time evolution and longitudinal difference although the equatorial ionization anomaly eia has been widely studied it was seldom investigated from observations for the topside ionosphere in this paper the climatology characteristics of the latitudinal structure of topside ion density ni were investigated in detail using rocsat 1 and dmsp ni observations eia double peak structure may exist at 600 km depending on longitude local time season and solar activity while it is not a prevalent characteristic at 840 km even at solar maximum sunset local time evolution of the eia at 600 km was presented the double peak structure begins to appear at noontime being later than the appearance of the eia in f2 peak region the pronounced eia induced by the strong prereversal enhancement at solar maximum begins to appear at 19 00 lt and can last to pre midnight eia crest to trough ratio ctr is largest lowest at march equinox june solstice and reaches a maximum at 20 00 lt in all seasons eia structure shows evident longitudinal difference pronounced eia exists around about 100 e at 13 00 lt at the two equinoxes and june solstice while it exists at more extensive longitudes about 90 e to 240 e at december solstice the trans equator plasma transport induced by neutral winds can weaken the double peak structure in the topside ionosphere the longitudinal difference in the eia structure at 600 km is related to the longitudinal variations of equatorial upward plasma drift and geomagnetic declination