water solubility in pyrope to 100 kbar the solubility and incorporation mechanism of water in natural almost pure pyrope from dora maira western alps was investigated the infrared spectrum of the natural untreated sample 58 ppm water shows several exceptionally sharp bands in the oh stretching region including a single band at 3601 9 cm 1 and a band system with main components at 3640 5 3650 8 and 3660 6 cm 1 high temperature and high pressure infrared spectra suggest that the two absorption features arise from almost free oh groups in sites with different compressibility and thermal expansivity with the site causing the 3601 9 cm 1 band being much stiffer pyrope samples were annealed in a piston cylinder or multi anvil apparatus for several days in the presence of excess water excess sio2 and excess al2sio5 to determine the equilibrium solubility of water in pyrope to 100 kbar total solubility increases with pressure however this is exclusively due to the high frequency band system while the intensity of the low frequency band decreases with pressure at 1000 c and the oxygen fugacity of the ni nio buffer the bulk solubility can be described by the equation c oh af h2o 0 5exp p v rt with a 0 679 ppm bar0 5 and v 5 71 cm3 mol this equation implies the incorporation of water in the crystal as isolated oh groups with increasing temperature solubility appears to decrease with h 14 kj mol at fe feo buffer conditions solubility is 30 to 50 lower than with the ni nio buffer suggesting that the incorporation of oh is not coupled to the reduction of fe3 possibly the 3601 9 cm 1 band is associated with the tetrahedral oh b defect and the high frequency system with the dodecahedral oh li defect based on the experimentally established solubility model it is estimated that garnet in a hot subducted slab will transport 170 ppm of water into the mantle beyond the breakdown limit of amphibole in a cold slab 470 ppm of water can be incorporated into garnet at the breakdown limit of phengite these numbers imply that a significant fraction of the total water in the hydrosphere has been recycled into the mantle since the proterozoic

guided wave propagation in laterally varying media ii lg waves in north western europe summary lg wave observations at norsar from a sequence of explosions straddling the central graben in the north sea show that the phase is almost extinguished by passing through this structure for models of the graben structure based on seismic refraction experiments with crustal thinning beneath a zone of thickened sediments numerical modelling of lg propagation shows very poor transmission the inclusion of attenuation simulating the effects of scattering from faults and other complex structures further diminishes the transmittivity the theoretical effect of a crustal pinch is to redistribute s energy over a wide range of groups velocities a pattern that fits well with the observations three components recordings at norsar of explosive charges fired in water covering a wide range of azimuths show significant transverse components to the seismograms the transverse energy builds up with travel time and for lg is of the same order as the vertical component these results are consistent with the theoretical prediction of progressive net transfer of energy from rayleigh to love modes as the wavetrain propagates through a three dimensionally heterogeneous medium

a transitional eclogite to high pressure granulite facies overprint on coesite eclogite at taohang in the sulu ultrahigh pressure terrane eastern china abstract a transitional eclogite to high pressure granulite facies paragenesis omp pl qtz grt after peak coesite eclogite facies metamorphism and predating the later amphibolite facies overprint is identified in coesite eclogite from the taohang area of the sulu ultrahigh pressure uhp terrane in eastern china these minerals were equilibrated at 17 kbar and 820 c this reveals that fluid infiltration might activate retrograde recrystallisation even at a deep level during the exhumation process of the uhp rocks the tectono metamorphic significance of the unusually high pressure overprint is also discussed

coesite and pure pyrope in high grade blueschists of the western alps a first record and some consequences a pyrope quartzite originally described by vialon 1966 from the dora maira massif was resampled and reinvestigated garnet up to 25 cm in size phengite kyanite talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz the garnet is a pyrope almandine solid solution with 90 to 98 mol mg end member it contains inclusions of coesite which has partially inverted to quartz resulting in a typical radial cracking of the host garnet around the inclusions several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite

seismic recognition of local inhomogeneities a simple method to contour local inhomogeneities using seismic data is proposed it formalizes an approximate inversion method which is based on the interpretation of local inhomogeneities as making the differences between an actual seismic data set and a previous reference model it uses the optimal statistical criteria of parameter estimation and recognition and the ray representation of the waves spreading any combination of direct reflected and or other types of waves may be used as the database inhomogeneities having a size two times above the wavelength of the seismic waves can be resolved laboratory experiments using ultrasonic waves and analysis of data from field experiments confirmed the theoretical results the method can be used to search for ore bodies kimberlite cubes oiltraps etc

grain scale pressure variations and chemical equilibrium in high grade metamorphic rocks in the classical view of metamorphic microstructures fast viscous relaxation and so constant pres sure is assumed with diffusion being the limiting factor in equilibration this contribution is focused on the only other possible scenario fast diffusion and slow viscous relaxation and brings an alter native interpretation of microstructures typical of high grade metamorphic rocks in contrast to the pressure vessel mechanical model applied to pressure variation associated with coesite inclusions in various host minerals a multi anvil mechanical model is proposed in which strong single crystals and weak grain boundaries can maintain pressure variation at geological time scales in a polycrystalline material in such a mechanical context exsolution lamellae in feldspar are used to show that feldspar can sustain large differential stresses 10 kbar at geological time scales furthermore it is argued that the existence of grain scale pressure gradients combined with diffusional equilibrium may explain chemical zoning preserved in reaction rims assuming zero net flux across the microstructure an equilibrium thermodynamic method is introduced for inferring pressure variation corresponding to the chemical zoning this new barometric method is applied to plagioclase rims around kyanite in fel sic granulite bohemian massif czech republic yielding a grain scale pressure variation of 8 kbar in this approach kinetic factors are not invoked to account for mineral composition zoning preserved in rocks metamorphosed at high grade

factors in the preservation of coesite the importance of fluid infiltration the survival of coesite in ultrahigh pressure uhp rocks is most commonly attributed to rapid exhumation continuous cooling during uplift and inclusion in strong phases that can sustain a high internal over pressure during decompression exceptions to all of these criteria exist perhaps less attention has been paid to the role of fluid infiltration in the preservation of coesite we used infrared spectroscopy to measure water contents of coesite and coesite pseudomorphs in a variety of uhp rocks in all cases oh concentrations in coesite are below the detection limit of 100 ppm h2o the silica phases surrounding coesite however show varying amounts of h2o this is most spectacularly observed in pyrope quartzites from the dora maira massif that contain at least three phases of silica replacing coesite also distinguished by varying color of cathodoluminescence cl palisade textured quartz 100 ppm h2o red violet cl mosaic quartz which is actually chalcedony up to 0 4 wt h2o yellow brown cl and a rare highly hydrated silica phase interpreted to be opal 7 wt h2o dark blue cl very similar signatures are observed in a grospydite xenolith from the roberts victor kimberlite the quartz replacing coesite in other uhp samples studied contains on the order of 500 ppm h2o or less and most measurements are under the detection limit of our technique we infer that palisade quartz forms under dry or nearly dry conditions and at high temperatures during dilation of the host phase the formation of hydrous silica phases such as chalcedony and opal however must take place at much lower temperatures after cracking of the host phase which allows external fluids to infiltrate delay of fluid infiltration to low temperatures where kinetics are slow even in the presence of water is the most critical factor in the preservation of coesite

water content in natural eclogite and implication for water transport into the deep upper mantle abstract infrared spectroscopy and ion micro probe measurements showed that the major constituent minerals of eclogites from the kokchetav massif which have been subducted to 180 km depths contain significant amounts of water up to 870 ppm h 2 o by weight in omphacite 130 ppm h 2 o in garnet and 740 ppm h 2 o in rutile omphacite shows three hydroxyl absorption bands at 3440 3460 3500 3530 and 3600 3625 cm 1 garnet has a single band at 3580 3630 cm 1 and rutile has a single sharp band at 3280 cm 1 the hydroxyl absorbance at these wavenumbers changes with the crystal orientation in polarized infrared radiation indicating that the water is structurally incorporated in these minerals the water contents in omphacite and garnet increase systematically with the metamorphic pressure of the host eclogites the partitioning coefficient of the water content between coexisting garnet and omphacite is similar in different eclogites d grt omp 0 1 0 2 but decreases slightly at high pressure based on the mineral proportions of the eclogites we estimate bulk rock water content in the eclogites ranging from 3070 to 300 ppm h 2 o by weight although hydrous minerals are absent in the diamond grade eclogite 60 kbar and 1000 c trace amounts of water are incorporated in the nominally anhydrous minerals such as omphacite and garnet the presence of significant water in these minerals implies that the subducting oceanic crust can transport considerable amounts of water into the deep upper mantle beyond the stability of hydrous minerals such water may be stored in the deep upper mantle and have an important influence on dynamics in the earth s interior

prograde high to ultrahigh pressure metamorphism and exhumation of oceanic sediments at lago di cignana zermatt saas zone western alps pelagic metasediments and morb type metabasalts of the former tethyan oceanic crust at cignana valtournanche italy experienced uhp metamorphism and subsequent exhumation during the early to late tertiary maximum pt conditions attained during uhp metamorphism were 600 630 c 2 7 2 9 gpa which resulted in the formation of coesite glaucophane eclogites in the basaltic layer and of garnet dolomite aragonite lawsonite coesite phengite bearing calc schists and garnet phengite coesite schists with variable amounts of epidote talc dolomite na pyroxene and na amphibole in the overlying metasediments during subduction the rocks followed a prograde hp uhp path which in correspondance with the jurassic age of the tethyan crust reflects the thermal influence of relatively old and cold lithosphere and of low to moderate shear heating inflections on the prograde metamorphic path may correspond to thermal effects that arise from a decrease in shear heating due to brittle plastic transition in the quartz aragonite dominated rocks induced convection in the asthenospheric mantle wedge and or heat consumption by endothermic reactions over a restricted pt segment during subduction after detachment from the downgoing slab some 50 70 ma before present the cignana crustal slice was first exhumed to ca 60 km and concomitantly cooled to ca 550 c tracing back the uhp hp prograde path displaced by 50 80 c to higher temperatures exhumation at this stage is likely to have occurred in the benioff zone while the subduction of cool lithosphere was going on subsequently the rocks were near isothermally exhumed to ca 30 km followed by concomitant decompression and cooling to surface conditions at 500 c 1 gpa during this last stage the uhpm slice arrived at its present tectonic position with respect to the overlying greenschist facies combin zone in contrast to the well preserved hp uhpm record of the coesite glaucophane eclogites the hp uhp assemblages of the metasediments have been largely obliterated during exhumation relics from which the metamorphic evolution of the rocks during prograde hp metamorphism and the uhp stage can be retrieved are restricted to rigid low diffusion minerals like garnet dolomite tourmaline and apatite

kinetics of the coesite quartz transition application to the exhumation of ultrahigh pressure rocks the kinetics of the quartz coesite phase transition has been studied in situ by x ray diffraction in the 2 1 3 2 gpa 5001010 c pressure temperature range analysis of the data within cahn s model of nucleation and growth at grain boundaries reveals that the prograde and retrograde reactions have different kinetics the quartz coesite transformation is one order of magnitude faster than coesite quartz both reactions are characterized by high nucleation rates so that the overall reaction kinetics is controlled by crystal growth processes for the coesite quartz transformation growth rates are extrapolated using turnbull s equation with an activation energy for the transition of 163 23 kf mol this kinetic law is combined with an inclusion in a host elastic model to study the contribution of kinetics in coesite preservation this numerical modelling shows that above 400degreesc retrograde transformation of coesite to quartz is mainly controlled by the pressure vessel effect of the host phase whereas reaction kinetics is the controlling factor at lower temperatures the influence of the shape of the p t path and the exhumation rate upon the retrogression of coesite to quartz are investigated to use the percentage of unretrogressed coesite inclusions to constrain p t t paths

the high pressure single crystal elasticity of pyrope grossular and andradite high pressure brillouin scattering experiments were conducted on three natural singlecrystal garnets with near end member compositions pyrope mg3al2si3o12 grossular ca3al2si3o12 and andradite ca3fe 31 2si3o12 acoustic velocities of the samples were measured from the samples at pressures to 10 gpa in a diamond anvil cell with a methanolethanol water pressure medium elastic stiffness constants cij and their pressure dependencies cij p were calculated as were aggregate elastic moduli ks and g and their respective pressure derivatives the cauchy relations changed with pressure for both grossular and andradite suggesting that assuming these are constant is not valid for extrapolation to high pressures for these and possibly other minerals the variation in ks dp and g p was sensitive to composition and required a complex mixing model for extrapolation of end member elasticity values from garnets of intermediate compositions

grain scale deformation in ultra high pressure metamorphic rocks an indicator of rapid phase transformation abstract conspicuous grain scale deformation is observed in some ultra high pressure uhp metamorphic rocks of the dora maira massif western alps although no significant strain is discernible on the mesoscopic scale in a jadeite kyanite quartz rock some of the jadeite crystals reveal 100 deformation twins indicating local differential stress levels above 0 3 gpa many kyanite crystals show marked kink or deformation bands with a slip system 100 001 in contrast the adjacent coarse grained quartz matrix grain size ca 0 2 mm which has formed from coesite during exhumation from 100 km depth reveals a foam structure the quartz grain boundary configuration is controlled by interfacial free energy the grains are optically strain free and there is no crystallographic preferred orientation preservation of this foam microstructure which indicates grain growth during low stress annealing precludes that deformation of the jadeite and kyanite crystals is a result of a late stage low temperature overprint the orientation distribution of jadeite and kyanite with and without twins or deformation bands respectively has been investigated with a combination of universal stage and ebsd techniques on the scale of a thin section there is no preferred orientation of twinned jadeite and bent kyanite crystals and undeformed crystals respectively thus the orientation of the inferred local shortening direction is random this precludes deformation driven by a homogeneous far field tectonic stress but suggests an internally controlled stress field which is highly inhomogeneous on the scale of a few grain diameters laboratory experiments show that the coesite to quartz transformation proceeds within hours after decompression from 3 0 to 2 7 gpa at 800 c the microstructures of incompletely transformed samples indicate that the quartz growing at the expense of coesite undergoes crystal plastic deformation and recrystallizes with a very fine grain size during transformation in this case the deformation of quartz is attributed to the volumetric strain v 10 inherent in the coesite quartz transformation which causes a highly inhomogeneous stress field inside the sample related to the progress of the transformation we propose that a similar process has taken place in the polyphase natural rock during exhumation with the transient stresses causing mechanical twinning of jadeite and bending or kinking of kyanite when the transformation had gone to completion grain growth obliterated the microstructures of the quartz matrix while the deformed jadeite and kyanite crystals preserved the record of inhomogeneous deformation at high temperatures the peak differential stresses locally exceeded 0 3 gpa which indicates very high strain rates and a correspondingly rapid transformation of coesite to quartz comparable to the laboratory results

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

the influence of oh in coesite on the kinetics of the coesite quartz phase transition metastable coesite is an important pressure indicator for ultrahigh pressure rocks however in many cases coesite does not survive exhumation but reacts back to quartz although it was shown experimentally that incorporation of h in coesite increases with increasing pressure most coesite relics found in nature are essentially dry i e oh concentrations are below detection limit 1 wt ppm h2o thus does the incorporation of h promote the back reaction of coesite to quartz during exhumation the influence of intrinsic oh on the kinetics of the coesite quartz phase transition was determined using synthetic dry coesite with approximate to10 wt ppm h2o and wet coesite with approximate to105 wt ppm h2o tem analysis of the quenched samples proved the presence and absence of water in the wet and dry samples respectively the kinetics of the coesite quartz transition was investigated in situ using the multi anvil apparatus max 80 at the hamburger synchrotron radiation laboratory hasylab the transition rates were measured by observing changes in selected diffraction line intensities as a function of time the transformation and growth rates were derived using cahn s model of nucleation and growth at grain boundaries under the same experimental conditions the transformation rate of the wet coesite is more than ten times higher than that of the dry coesite this difference may explain why oh bearing natural coesite is rare this study reveals the importance of structurally bound oh for the kinetics of phase transitions of nominally anhydrous minerals

intergranular coesite and coesite inclusions in dolomite from the dabie shan constraints on the preservation of coesite in uhp rocks intergranular coesite is extremely rare in and bears crucial information on the formation and preservation of ultrahigh pressure uhp rocks here we report the first occurrence of intergranular coesite in a metasedimentary rock which occurs in the ganjialing area in the dabie shan east central china and contains abundant coesite inclusions in both garnet and dolomite we investigated the content of structural water in these minerals with fourier transform infrared spectroscopy our new results undermine the ubiquity of the pressure vessel model and highlight the role of reaction kinetics in preserving coesite due to the availability of water in uhp rocks this article is protected by copyright all rights reserved

quantitative analysis of trace oh in garnet and pyroxenes to calibrate infrared ir spectroscopy for quantitative analysis of trace structural oh in specific minerals we have determined concentrations of h in pure separates of mantle derived pyrope garnet 56 6 ppm h 2o by weight augite 268 8 ppm h 2o and enstatite 217 11 ppm h 2o by manometry after heating the samples and extracting h 2 gas under vacuum ir spectroscopy confirmed the presence of intrinsic oh in these samples prior to extraction and indicated between 86 and 100 removal of h during the extraction procedure the integral specific absorption coefficients of 1 39 0 14 l 7 09 0 32 and 15 6 0 94 ppm h 2o cm 2 for pyrope augite and enstatite respectively allow precise spectroscopic determination of the oh content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million uncertainties in accuracy depend on mineral composition and characteristics of the oh absorption spectrum and are estimated to range between 10 and 50

occurrences of intergranular coesite in ultrahigh p rocks from the sulu region eastern china implications for lack of fluid during exhumation several coesite grains along garnet omphacite grain boundaries were discovered in eclogites from yangkou beach of the sulu region eastern china these grains exhibit variable extents of conversion of coesite to palisade through mosaic to granoblastic quartz aggregates the rare occurrence of intergranular and matrix coesite in ultrahigh pressure uhp crustal rocks is related to the fast rate of exhumation and the low amount of fluid infiltration required during retrograde recrystallization sluggish reactions due to the lack of fluid in both uhp and retrograde metamorphism resulted in the occurrence of intergranular coesite in these eclogites the preservation of gabbroic texture and relict igneous minerals and the metastable persistence of low p assemblages in the coesite stability field

two years in the life of a mediterranean salt lens abstract a lens of mediterranean water meddy was tracked in the eastern north atlantic for two years with sofar floats the meddy was first found between the canary islands and the azores in october 1984 it center moved in an irregular pattern at speeds of a few cm s 1 and translated 1100 km to the south in two years this meddy was surveyed four times by ctd and velocity profilers and once with the microstructure profiler epsonde when observed during the first two surveys the meddy had a core that was stably and smoothly stratified in both salinity and temperature nearly uniform in the horizontal and was saltier than the surrounding ocean by 0 65 psu the meddy was eroded from its edges top and bottom and lost salt and hat with an e folding time of about one year the salinity at the center remained at its original value during the first year and decreased during the second year evidence was seen for mixing by lateral intrusions double diffusion and turbulence the intrusions are thought to

coesite inclusions and prograde compositional zonation of garnet in whiteschist of the hp uhpm kokchetav massif kazakhstan a record of progressive uhp metamorphism coarse grained whiteschist containing the assemblage garnet kyanite phengite talc quartz coesite is an abundant constituent of the ultrahigh pressure metamorphic uhpm belt in the kulet region of the kokchetav massif of kazakhstan garnet displays prograde compositional zonation with decreasing spessartine and increasing pyrope components from core to rim cores were recrystallized at t 380 c inner to 580 c outer at p 10 kbar garnet ilmenite geothermometry margarite quartz stability and mantles at t 720 760 c and ph20 34 36 kbar coesite graphite stability phengite geobarometer kfmash system reaction equilibria textural evidence indicates that rims grew during decompression and cooling within the qtz stability field silica inclusions quartz and or coesite of various textural types within garnets display a systematic zonal distribution cores contain abundant inclusions of euhedral quartz type 1 inclusions inner mantle regions contain inclusions of polycrystalline quartz pseudomorphs after coesite type 2 with minute dusty micro inclusions of chlorite and more rarely talc and kyanite in their cores intense radial and concentric fractures are well developed in the garnet intermediate mantle regions contain bimineralic inclusions with coesite cores and palisade quartz rims type 3 which are also surrounded by radial fractures subhedral inclusions of pure coesite without quartz overgrowths or radial fractures type 4 occur in the outer part of the mantle garnet rims are silica inclusion free type 1 inclusions in garnet cores represent the low p low t precursor stage to uhpm recrystallization and attest to the persistence of low p assemblages in the coesite stability field coesites in inclusion types 2 3 and 4 are interpreted to have sequentially crystallized by net transfer reaction kyanite talc garnet coesite h2o and were sequestered within the garnet with progressively decreasing amounts of intragranular aqueous fluid during the retrograde evolution of the rock all three inclusion types diverged from the host garnet p t path at the coesite quartz equilibrium and followed a trajectory parallel to the equilibrium boundary resulting in inclusion overpressure coesite in type 2 inclusions suffered rapid intragranular h2o catalysed transformation to quartz and ruptured the host garnet at about 600 c when inclusion p 27 kbar garnet host p 9 kbar instantaneous decompression to the host garnet p t path passed through the kyanite talc chlorite quartz reaction equilibrium resulting in the dusty micro assemblage in inclusion cores type 3 inclusions suffered a lower volumetric proportion transformation to quartz at the coesite quartz equilibrium and finally underwent rupture and decompression when t 400 c facilitating coesite preservation type 4 coesite inclusions are interpreted to have suffered minimal transformation to quartz and proceeded to surface temperature conditions along or near the coesite quartz equilibrium boundary

interfacial friction induced pressure and implications for the formation and preservation of intergranular coesite in metamorphic rocks abstract the finding of intergranular coesite and coesite pseudomorphs has been taken as critical evidence to support that the formation of coesite was related to regional ultrahigh pressure uhp metamorphism rather than the pressure vessel effect previous laboratory deformation experiments found that coesite occurs in practically undeformed strain forbidden zones immediately adjacent to the piston sample interfaces while the mean stress applied to the specimen is remarkably lower than the quartz coesite equilibrium boundary the formation and preservation of intergranular coesite in eclogites from uhp metamorphic terranes and the occurrence of coesite in strain forbidden zones within experimentally deformed rocks can be more satisfactorily explained by the theory of interfacial friction induced pressure which is a well known in metal forging during certain episodes of fast tectonic deformation under high transient differential stresses the interfacial friction can induce very significant deformation pressures in thin layers of weak materials e g sio2 between large garnet crystals that are refractory and mechanically strong thus act as excellent anvils the local deformation pressure which deviates from the lithostatic value is likely an intrinsic property of highly constrained flows of weak materials between strong walls at least on a microstructural scale

kinetics of the coesite to quartz transformation abstract the survival of coesite in ultrahigh pressure uhp rocks has important implications for the exhumation of subducted crustal rocks we have conducted experiments to study the mechanism and rate of the coesite quartz transformation using polycrystalline coesite aggregates fabricated by devitrifying silica glass cylinders containing 2850 h 10 6 si at 1000 c and 3 6 gpa for 24 h conditions were adjusted following synthesis to transform the samples at 700 1000 c at pressures 190 410 mpa below the quartz coesite equilibrium boundary reaction proceeds via grain boundary nucleation and interface controlled growth with characteristic reaction textures remarkably similar to those seen in natural uhp rocks we infer that the experimental reaction mechanism is identical to that in nature a prerequisite for reliable extrapolation of the rate data growth rates obtained by direct measurement differ by up to two orders of magnitude from those estimated by fitting a rate equation to the transformation time data fitting the rates to turnbull s equation for growth therefore yields two distinct sets of parameters with similar activation energies 242 or 269 kj mol but significantly different pre exponential constants extrapolation based on either set of growth rates suggests that coesite should not be preserved on geologic time scales if it reaches the quartz stability field at temperatures above 375 400 c the survival of coesite has previously been linked to its inclusion in strong phases such as garnet that can sustain a high internal pressure during decompression other factors that may play a crucial role in preservation are low fluid availability possibly even less than that of our nominally dry experiments and the development of transformation stress which inhibits nucleation and growth these issues are discussed in the context of our experiments as well as recent observations from natural rocks

an anticlockwise p t t path at high pressure high temperature conditions for a migmatitic gneiss from the island of fjortoft western gneiss region norway indicates two burial events during the caledonian orogeny

deep subduction of felsic rocks hosting uhp lenses in the central saxonian erzgebirge implications for uhp terrane exhumation abstract contrasting metamorphic conditions determined by chemical geothermobarometric investigations of ultrahigh pressure uhp lenses surrounded by high pressure hp and medium pressure mp felsic country rocks are an enigmatic feature of uhp terranes one of the major questions arising is whether the uhp lenses and the country rocks are a product of different peak metamorphic conditions corresponding to different maximum depth or whether country rocks also experienced uhp conditions but equilibrated and or re equilibrated at a different metamorphic stage here we address this question to the central saxonian erzgebirge in the northwestern bohemian massif germany in order to screen the variety of garnet from lithologies occurring in the study area we analyzed the detrital garnet record from seven modern stream sands in addition to 700 inclusion bearing garnet grains previously studied from the 125 250 m grain size fraction we analyzed the 63 125 and 250 500 m fractions and extended the dataset to overall 2100 inclusion bearing grains the new findings of coesite and diamond inclusions in several garnet grains which are in compositional contrast to garnet of the known uhp lenses but match with those of the felsic country rocks show that considerable parts of the country rocks underwent uhp metamorphism melt inclusions containing cristobalite kokchetavite and kumdykolite in garnet derived from the country rocks point to partial melting and re equilibration during exhumation at hp ht conditions although an amalgamation of rocks which reached different maximum depth may be responsible for some of the contrasting peak metamorphic conditions the mineralogical evidence for uhp conditions in the felsic country rocks surrounding the uhp lenses proves a largely coherent slab subducted to uhp conditions furthermore the presence of coesite in the subducting voluminous felsic crust and its transformation to quartz during exhumation have great implications for buoyancy development during the metamorphic cycle which may explain the high exhumation rates of uhp terranes

coesite in subducted continental crust p t history deduced from an elastic model abstract coesite has been found in a metasedimentary rock in a continental unit of the western alps dora maira massif the rock preserves the high pressure low temperature assemblage of nearly pure pyrope talc phengite kyanite in a quartz matrix coesite exclusively occurs as inclusions in pyrope and is partly inverted to quartz textural observations and mechanical considerations suggest that the rock crystallised in the coesite stability field a simple elastic model for a coesite inclusion in pyrope explains why coesite has been exclusively preserved in the inclusions and not in the matrix combined with petrological data the model constrains the crystallisation conditions of the pyrope coesite rock p 28kbar 650 this finding has an important bearing on the significance of p t conditions estimated from minerals occurring as inclusions and on the actual behaviour of continental crust in collision zones

seismic tomography 3 d image of upper mantle attenuation beneath the kanto district japan abstract with the same principle as being used in medical x ray imaging the absorption of s waves is utilized to map attenuation variations in the upper mantle beneath the kanto district japan where the existence of two sinking slabs the pacific and the philippine sea slabs is inferred nearly 4500 seismic intensity reports on local shallow and intermediate earthquakes are used as measures of the maximum ground acceleration of s waves which are assumed to be radiated isotropically from earthquake foci an ordinary damped least squares inversion is employed to obtain the attenuation structure the inversion reveals a remarkable contrast of the attenuation coefficient and three prominent features the first is a low attenuation zone corresponding to the descending philippine sea slab the attenuation mapping suggests that an aseismic portion of the philippine sea slab continues to a depth of 120 km toward the north the second feature is a hard root low attenuation zone of the plate bearing the japanese islands attaining at least a depth of 60 km beneath the northeastern part of the kanto region this root appears to be responsible for the anomalously deep interplate seismicity in this area where a strong seismic coupling exists at a depth of 40 70 km between the surficial plate and the underlying philippine sea slab the third feature is a zone of extremely high attenuation in the upper mantle lying on the continental side of the volcanic front where many quaternary volcanoes are located especially a spot of very high attenuation is found at a depth of 60 90 km beneath an active volcano mt fuji

nonlinear equilibration of thermohaline intrusions abstract the nonlinear behavior of thermohaline intrusions on a wide front is investigated using a one dimensional numerical model the model is used to follow the evolution of a field of intrusions from infinitesimal amplitude to a large amplitude state characterized by inversions in temperature and salinity it is thus possible to extend the analytical studies of toole and georgi and others to large amplitude allowing for the effects of amplitude dependent diffusivities and for the appearance of stably stratified diffusively stratified and statically unstable regions in the water column as the intrusions grow the model runs are initialized with infinitesimal disturbances that grow exponentially in time until inversions in temperature and salinity occur after inversions appear the intrusions evolve toward an equilibrium state in which friction balances buoyancy forces for both finger and diffusive sense basic state stratifications these equilibrium states are characterized by statically unstabl

coesite inclusions in dolomite from eclogite in the southern dabie mountains china the significance of carbonate minerals in uhpm rocks coesite inclusions have been discovered in dolomite from carbonate bearing eclogite in the dabie uhp terrane the eclogite boudins are enclosed in calc silicate rocks that contain quartz aggregatesafter coesite in the matrix the carbonate bearing eclogite is composed of garnet coesite or quartz dolomite magnesite omphacite rutile tminor phengite apatite and zircon and was formed at 760 dc 28 kbar and 0 01 100 km

the pressure path of solid inclusions in minerals the retention of coesite inclusions during uplift abstract an inclusion model allows calculation of the stresses in and around minerals included in other minerals during changes in pressure and temperature the equations are applied to illustrate cooling and uplift histories of quarzo feldspathic rocks from 500 c and various pressures to ambient conditions even in the absence of pore fluid pressure microfractures may open at external pressures of 200 400 mpa and temperatures of 200 400 c due to differential volume changes of the constituent minerals coesite included in garnet cannot have formed during progressive metamorphism from quartz at lithostatic pressures below the coesite stability field because of differential volume changes coesite inclusions are captured by their host minerals at ultra high pressures and they persist to lower pressures because of the large volume increase occurring at the coesite to quartz transition the pi t path followed by the sio2 inclusion traces the boundary between the stability fields of coesite and quartz until radial fractures develop in the host at low external pressure

present day ultrahigh pressure conditions of coesite inclusions in zircon and garnet evidence from laser raman microspectroscopy coesite the dense high pressure polymorph of quartz occurs as inclusions in mechanically strong minerals in deeply subducted metamorphosed crustal rocks in a number of eurasian collisional orogens it is the primary indicator mineral of ultrahigh pressure p metamorphism whereas some coesite inclusions are untransformed most exhibit partial transformation to palisade quartz and a concomitant increase in volume resulting in rupture and radial fracturing of the host grain coesite can be identified by its diagnostic raman spectrum the strongest band at atmospheric pressure room temperature is at 521 cm 1 laser raman microspectroscopic analyses of coesite inclusions within garnet and zircon in ultrahigh p metamorphic rocks from kazakhstan indonesia and china reveal consistent differences in the raman spectra of 1 partially transformed coesite quartz main raman band at 521 cm 1 and 2 untransformed monomineralic coesite grains main band at 525 526 cm 1 applying the room temperature calibration of pressure dependence of the coesite raman spectrum we conclude that the latter coesite inclusions are subject to a remarkable pressure differential of 19 23 kbar with the host grains and are still undergoing pressure temperature conditions on or close to the quartz coesite equilibrium boundary

the oh content of pyrope at high pressure the oh contents of pyrope garnets synthesised at 1000 c and pressures between 2 and 13 gpa have been measured by infrared spectroscopy we find that under the same conditions of pressure temperature ah2o and asio2 the oh content of pyrope is similar to that of grossular this shows that observed differences in nature between water contents of pyrope and grossular are related to paragenesis rather than reflecting higher intrinsic solubility in grossular in the presence of excess sio2 the h2o content increases with pressure to 5 gpa 1000 ppm then decreases to below the detection limit at pressures above 7 gpa thus garnet becomes more hydrous with pressure to some critical value beyond which dehydration occurs even under h2o saturated conditions this observation is consistent with the measured partial molar volume of water in hydrogarnet which becomes greater than that in fluid water within the pressure range of this study when corrected to upper mantle conditions we find that pyrope should dehydrate with increasing depth below about 250 km pyrope is unlikely therefore to be a major site of water storage in the transition zone and upper mantle