coesite eclogites from the roberts victor kimberlite south africa abstract coesite or pseudomorphic quartz is more common than previously recognized in the eclogite xenolith suite from the roberts victor mine south africa all coesite eclogites in this study 18 samples are classified as group i and have mineral compositions that span virtually the entire compositional range of group i eclogites described from this locality most of the roberts victor group i eclogite suite may be in equilibrium with free silica thus weakening the case for these rocks representing residues of partial melting oxygen isotope compositions of garnets from 15 samples are in the range 5 32 6 95 similar to other roberts victor group i eclogites these observations are consistent with a model in which protoliths of these rocks were oceanic basalts and intrusive rocks that underwent exchange with seawater at relatively low temperatures to variable extents prior to subduction and metamorphism to eclogite facies without suffering significant partial melting during or following subduction

new constraints on the 138la β decay constant based on a geochronological study of granites from the yilgarn block western australia abstract the decay constant of 138 la has been geochronologically determined using archean granites from the yilgarn block western australia rb sr and sm nd mineral isochron ages were obtained for the two granite samples which are nearly identical with the ion microprobe u pb zircon ages this agreement indicates that the closure date for these samples is the same within analytical error making them suitable for geochronological estimation of the decay constant for 138 la applying a new method of ce isotope analysis with analytical reproducibility of 0 008 la ce isotope data for the studied samples resulted in precise mineral isochrons based on these internal mineral isochrons and ages determined by other geological clocks the decay constant for 138 la was estimated to be 2 33 0 24 10 12 a 1 2

variations in trapping temperatures and trace elements in peridotite suite inclusions from african diamonds evidence for two inclusion suites and implications for lithosphere stratigraphy the proton microprobe has been used to measure the trace element contents of cr pyrope olivine and orthopyroxene inclusion di in 60 diamonds from southern africa and in concentrate garnets from the host kimberlites olivine inclusions show a negative correlation of ca with fo content but olivines coexisting with very subcalcic garnets are anomously depleted in ca relative to fo the maximum and median values of ti zn ga zr and y in di garnets decrease as ca decreases relative to cr consistent with increasing depletion by removal of silicate melts however the most subcalcic garnets are anomously enriched in sr and lree the contrasting depletion in zr y ti etc and enrichment in sr is not consistent with a single stage depletion event the extreme ca depletion of the most subcalcic garnets and their coexisting olivines and the sr enrichment are interpreted as the result of metasomatism by a carbonatitic fluid following depletion trapping temperatures of garnet di estimated by nickel thermometry range from 950 to 1500 c most di with t 1200 c are lherzolitic rather than subcalcic in most pipes studied the trapping t of di garnets is higher than the t range of equivalent garnets from concentrates the high ts are interpreted as reflecting the formation of diamonds during short lived thermal pulses followed by cooling toward a conductive geotherm the t distribution of calcic and subcalcic garnets in concentrates from kimberlites suggests that lherzolite and harzburgite are intimately intermixed over the depth range 150 180 km beneath the kalahari craton the abundance of calcic garnets with t 1200 c suggests the presence of significant amounts of lherzolite at greater depths this deeper lherzolite may be associated with eclogite and may be the source region for some high t lherzolitic di garnets

infiltration driven dehydration and anatexis in granulite facies metagabbro grenville province ontario canada dark hornblende garnet rich quartz absent metagabbro boudins from the seguin subdomain ontario grenville province are transected by anastomosing light coloured veins rich in orthopyroxene clinopyroxene plagioclase and sometimes quartz the veins vary in texture from fine grained diffuse veins and patches that overprint the metagabbro to coarse tonalitic leucosomes with sharp borders the diffuse veins and patches are suggestive of channellized subsolidus dehydration of the metagabbro while the tonalitic leucosomes are suggestive of local internally derived anatexis all vein types grade smoothly into each other with the tonalitic leucosomes being the latest relative to the host metagabbro the veins have higher si na ba sr lower fe mg ca ti and similar al the coarser veins are enriched in k plagioclase becomes steadily enriched in na in the transition from host metagabbro an47 to the veins an35 and in the coarsest veins it is antiperthitic differences in composition of the other minerals between host metagabbro and vein are minor pressure temperature estimates are scattered but indicate a minimum temperature during vein formation of 700 c at about 8 kbar mass balance constraints indicate that the veins formed from the metagabbro in an open system the transecting veins are interpreted to represent pathways of si na ba sr k al enriched low ah2o fluids that metasomatized the host metagabbro to form the anhydrous veins an initial period of localized solid state dehydration of the metagabbro represented by the diffuse veins was followed by a transition to localized anatexis represented by the tonalitic leucosomes the change to anatexis may have been due to the addition of k to the infiltrating fluid the source and delivery mechanism of the fluids is unknown

superzoned garnets in the coesite bearing brossasco isasca unit dora maira massif western alps and the origin of the whiteschists abstract rare centimeter sized superzoned garnets szgs were discovered in two coesite bearing whiteschists of the brossasco isasca unit biu southern dora maira massif dmm western alps the superzoned garnet consists of a reddish brown almandine core crowded with inclusions of staurolite chloritoid kyanite chlorite and paragonite and of a pinkish pyrope rim with sporadic inclusions of kyanite and magnesian chlorite the core rim contact is relatively sharp and marks the termination of the inclusion rich portion the core composition of the superzoned garnet is almost identical to or slightly richer in mg than that of the rim of porphyroblastic garnet in metapelites from the same unit in the rim of the superzoned garnet mg fe ratio increases abruptly towards the outermost rim whose composition is identical to that of the common pyrope in the whiteschist at the core rim boundary there is no chemical gap chloritoid and staurolite are common inclusions in the core of the superzoned garnet in the whiteschist and in the porphyroblastic garnet in the metapelite the staurolite composition si 2 00 and total r 2 grt cld chl the resulting petrogenetic grid suggests that the core of the superzoned garnet contains incompatible assemblages such as st cld chl vs cld chl ky new and literature data and results of experiments in the kfash system suggest that 1 the superzoned garnet was formed under a single prograde high pressure ultra high pressure hp uhp alpine metamorphism 2 the almandine inclusion rich core of the superzoned garnet crystallized at disequilibrium in a pelitic composition system at around 600 c and less than 16 kbar probably from a former metapelite xenolith included in a variscan granitoid and 3 the chemical environment of the host rock suddenly changed from the normal pelite to the whiteschist composition by a metasomatic process during the rim growth i e at a stage close to the uhp climax

garnet sm nd data from the saualpe and the koralpe eastern alps austria chronological and p t constraints on the thermal and tectonic history abstract garnets from recrystallized staurolite and kyanite bearing mica schists from the central saualpe base ment representing the host rocks of the type locality eclogites give concordant sm nd garnet whole rockisochronagesbetween88 5 1 7and90 9 0 7ma themillimetre sized mostly inclusion freegrainsshowfairlyhomogeneouselement pro les withpyropecontentsof25 27 narrowrims withanincreasein fe and mn and a decrease in mg document minor local re equilibration during cooling accordingto phengite geothermobarometry peak metamorphic conditions at 90 ma were close to 20kbar and680 c and similar to those recorded by the eclogites the garnet rims record about 575 c 7kbar forthe nal stages of metamorphism a phengitic garnet mica schist sampled at the immediate contact withthe gertrusk eclogite gave a garnet whole rock sm nd age of 94 0 2 7 ma garnet porphyroclasts separated from a pegmatite mylonite of the koralpe plattengneiss near stainzare unzoned and show spessartine contents of 15 composition and sm nd ages of close to 260 mapoint to a magmatic origin for these garnets the garnet data from the saualpe document an intense alpine metamorphism for this part of theaustroalpine basement the mica schists recrystallized during decompression and rapid exhumation atthe nal stages of and immediately following a high p event the koralpe data show that high alpinetemperatures did not reopen the sm nd isotope system implying a closure temperature in excess of c 600 c for this isotopic system in garnet key words alpine orogenesis closure temperature eastern alps high p metamorphism metamorphicand magmatic garnets p t t paths saualpe koralpe basement sm nd geochronology

a classification scheme for mantle derived garnets in kimberlite a tool for investigating the mantle and exploring for diamonds abstract a new empirical method has been devised for classification of mantle derived garnets in kimberlite simple chemical screens have been developed to distinguish between garnets from different parageneses based on mg fe ca cr ti and na values of published analyses of garnets from 2000 ultramafic xenoliths in kimberlite although crustal garnets are typically uncommon as xenocrysts in kimberlite the first step in the classification is to screen these from the mantle population using data from 600 garnet bearing crustal rocks such a screen may also prove useful in evaluating the source crust vs mantle of garnet in kimberlite exploration samples subsequent steps divide mantle garnets into eclogite peridotite and cr poor megacryst groupings and sub groups of the peridotite lherzolite harzburgite wehrlite and eclogite groups i and ii and a b c and grospydite populations important features of this classification include the fact that it is based on distinctions between groups of fundamental geological significance e g peridotite vs eclogite and it is based on a large well documented and well understood xenolith database as it utilizes oxide values and molar ratios of major and minor elements the rationale for the screens is readily understood and it is simple to use

tectono metamorphic evolution of the karakorum metamorphic complex dassu askole area ne pakistan exhumation of mid crustal ht mp gneisses in a convergent context the south karakorum margin east of the himalayan syntaxis consist of an e w elongated zone of young 10 3 ma high grade metamorphic rocks m2 and related migmatitic domes this late tectono metamorphic event post dates the palaeogene 55 37 ma phase of thickening of the belt featured by nw se structures and associated m1 amphibolite facies metamorphism 0 7 gpa 700 c this m2 metamorphism is characterised by low pressure high temperature conditions coeval with migmatite formation in response to a thermal increase of c 150 c compared to m1 culminating at a temperature of c 770 c and a pressure of 0 5 0 6 gpa rapid exhumation of migmatitic domes at a rate of 5 mm yr 1 was accommodated by vertical extrusion in the core of e w crustal scale folds these crustal scale folds formed in response to n s syn collisional shortening and were enhanced by thermal weakening of the migmatised continental crust m2 metamorphism is spatially and temporarily associated with granitoids showing a mantle affinity firmly suggesting that this could be the advective heat source for the granite and syenite generation and the subsequent migmatisation of the mid crustal level such relationships between a mantle related magmatism and a high temperature metamorphism in a convergent shortening context are suggestive of the breakoff of the subducted indian slab since 20 ma

hydration of orthopyroxene cordierite bearing assemblages at laouni central hoggar algeria in the laouni region central hoggar algeria retrogression of high grade orthopyroxene cordierite bearing rocks led to the crystallization of orthoamphibole and garnet and at a later stage of chlorite from the original paragenesis calculated phase diagrams show that this retrogression occurred at about 3 kbar with the simplest model involving hydration at 650 700 c and at around 500 c with the rocks experiencing ah2o less than 1 except possibly in the last stages of chlorite crystallization as the other rock types occurring in the same area as the orthopyroxene cordierite rocks display similar features it is concluded that regional hydration occurred presumably related to the release of fluids during the crystallization of the pan african granitic and mafic magmas that are widespread in the laouni area

evolution of high mg al granulites from sunkarametta eastern ghats india evidence for a lower crustal heating cooling trajectory a suite of high mg al granulites from sunkarametta eastern ghats belt india shows contrasting prograde assemblages of extremely aluminous orthopyroxene cordierite sapphirine and similarly aluminous orthopyroxene ti rich spinel in closely associated domains textural and compositional characteristics indicate that both were derived from prograde dehydration melting of biotite plagioclase quartz bearing protoliths the former assemblage was stabilized at relatively more magnesian bulk composition geothermobarometric data and petrogenetic grid considerations place peak metamorphic conditions at c 950 c and 9 kbar subsequent to peak metamorphism the rocks cooled to c 700 750 c with slight lowering of pressure and the retrograde reactions also involved melt solid interaction the inferred p t trajectory is one of heating cooling at lower crustal 25 30 km depths

thermobarometry of the bleikvassli zn pb cu deposit nordland norway the bleikvassli massive sulfide ore deposit is hosted by proterozoic pelitic quartzofeldspathic and amphibolitic rocks of the uppermost allochthon of the scandinavian caledonides staurolite garnet biotite and kyanite staurolite biotite assemblages indicate that metamorphism reached the kyanite zone of the amphibolite facies geothermobarometry was conducted on rocks in and around the deposit using a variety of silicate and sulfide calibrations temperature determinations are most reliant on the garnet biotite exchange reaction with analyses obtained from 259 garnet rims and adjacent biotite results from nine calibrations of the garnet biotite geothermometer are considered but compositional limitations of many calibrations involving high ca and mn contents in garnet and alvi and ti in biotite make many of the coexisting mineral pairs unsuitable average temperatures calculated from the two calibrations that most closely address the garnet biotite compositions observed at bleikvassli are 584 c 49 c and 570 c 40 c the application of two calibrations of the garnet staurolite geothermometer on a limited number of samples yields 581 c 2 c and 589 c 12 c assuming a h2o 0 84 based upon calculations of the modal proportions of gaseous species pressure determinations are less constrained phengite and plagioclase biotite garnet muscovite geobarometers give average pressures of approximately 5 0 kbar and 8 5 1 2 kbar respectively pressures obtained from the sphalerite hexagonal pyrrhotite pyrite barometer average 7 7 1 0 kbar in consideration of these results the peak metamorphic conditions at the bleikvassli deposit are estimated to be 580 c and 8 kbar

petrology and geothermobarometry of granulite facies metapelites from the hisoy torungen area south norway new data on the sveconorvegian p t t path of the bamble sector the high grade rocks metapelite quartzite metagabbro of the hisoy torungen area represent the south westernmost exposures of granulites in the proterozoic bamble sector south norway the area is isoclinally folded and a metamorphic p t t path through four successive stages m1 m4 is recognized petrological evidence for a prograde metamorphic event m1 is obtained from relict staurolite chlorite albite staurolite hercynite ilmenite cordierite sillimanite fine grained felsic material quartz and hercynite biotite sillimanite within metapelitic garnet the phase relations are consistent with a pressure of 3 6 0 5 kbar and temperatures up to 750 850 c m1 is connected to the thermal effect of the gabbroic intrusions prior to the main m2 sveconorwegian granulite facies metamorphism the main m2 granulite facies mineral assemblages quartz plagioclase k feldspar garnet biotite sillimanite are best preserved in the several metre wide al rich metapelites which represent conditions of 5 9 9 1 kbar and 790 884 c these p t conditions are consistent with a temperature increase of 80 100 c relative to the adjacent amphibolite facies terranes no accompanying pressure variations are recorded up to 1 mm wide fine grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction bt sil qtzgrt lq this dehydration reaction together with the absence of large scale migmatites in the area suggests a very reduced water activity in the rocks and xh2o 0 25 in the c o h fluid system was calculated for a metapelitic unit a low but variable water activity can best explain the presence or absence of fine grained felsic material representing a former melt in the different granulitic metapelites the strongly peraluminous composition of the felsic veinlets is due to the reaction grt former melt silcrd bt qtz h2o which has given poorly crystalline cordierite aggregates intergrown with well crystalline biotite the cordierite and biotite producing reaction constrains a steep first stage retrograde relative to m2 uplift path decimetre to metre wide strongly banded metapelites quartz plagioclase biotite garnet sillimanite inter layered with quartzites are retrograded to m3 amphibolite facies assemblages a p t estimate of 1 7 5 6 kbar 516 581 c is obtained from geothermobarometry based on rim rim analyses of garnet biotite plagioclase sillimanite quartz assemblages and can be related to the isoclinal folding of the rocks m4 greenschist facies conditions are most extensively developed in millimetre wide chlorite rich calcite bearing veins cutting the foliation

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

carbon isotope composition of graphite in mantle eclogites the carbon isotope composition 13c of primary graphite from 28 mantle derived eclogite xenoliths from kimberlites in southern africa and usa range from 14 31 to 2 84 pdb with a mean value of 6 2 both group i and group ii eclogites are represented by anomalously low carbon isotope ratios there is no simple correlation between isotopic composition and depth of origin demonstrating carbon isotopic heterogeneity in the shallow upper mantle not previously recognized but known from the deeper eclogite diamond population interpreted in the light of recent geochemical evidence supporting a subduction origin for some mantle eclogites and their diamonds low 13c graphite bearing eclogites could represent some of the earliest material emplaced beneath the cratons by subduction

cretaceous high p granulites at milford sound new zealand metamorphic history and emplacement in a convergent margin setting granulite facies orthogneiss of the arthur river complex arc at milford sound western fiordland records a complex early cretaceous magmatic and orogenic history for the pacific gondwana margin that culminated in the emplacement and burial of a dioritic batholith the western fiordland orthogneiss wfo enstatite bearing mafic to intermediate protoliths of the arc and wfo intruded the middle to upper crust the early deformation history of the arc is preserved in the pembroke granulite where two pyroxene s1 assemblages that reflect p 750 c were only patchily recrystallized during later deformation s1 is cut by garnet bearing leucogabbroic to dioritic veins which are cut by distinctive d2 fractures involving anorthositic veins and garnet diopside plagioclase bearing reaction zones these zones are widespread in the arc and wfo and record conditions of p 14 kbar and t 750 c garnet clinopyroxene bearing corona reaction textures that mantle enstatite in both the arc and wfo reflect early cretaceous burial by approximately 25 km of continental crust most of the arc is formed from the milford and harrison gneisses which contain steeply dipping s4 assemblages that envelop the pembroke granulite and involve garnet hornblende diopside clinozoisite rutile and plagio clase with or without kyanite the p t history of rocks in western fiordland reflects pronounced early cretaceous convergence related tectonism and burial possibly related to the collision and accretion of island arc material onto the pacific gondwana margin

fluid rock history of granulite facies humite marbles from ambasamudram southern india an extensive humite bearing marble horizon within a supracrustal sequence at ambasamudram southern india was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics at peak metamorphic temperatures of 775 73 c based on calcite graphite carbon isotope thermometry the mineral assemblages suggest layer by layer control of fluid compositions clinohumite calcite bearing assemblages suggest xco2 0 9 at 790 c and local wollastonite scapolite grossular bearing zones formed at xco2 of c 0 3 retrograde reaction textures such as scapolite quartz symplectites after feldspar and calcite and replacement of dolomite diopside or tremolite dolomite after calcite forsterite or calcite clinohumite are indicative of retrogression under high xco2 conditions calcite preserves late proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting isotopic zonation of calcite and graphite grains was likely produced by localized co2 fluid infiltration during retrogression contrary to the widespread occurrence of humite marbles related to retrograde aqueous fluid infiltration the ambasamudram humite marbles record a prograde to peak metamorphic humite formation and retrogression under conditions of low xh2o

metamorphic evolution of garnet epidote biotite gneiss from the moine supergroup scotland and geotectonic implications metapelitic gneisses from the glenfinnan group of the moine supergroup scotland contain sparse large and numerous small garnets associated with complex zoned epidote and plagioclase in a biotite matrix the large garnets show four zones ai aiv whereas the small garnets show three or fewer zones indicating successive garnet nucleation with increasing nucleation densities garnet zones ai and aiv grew under static conditions whereas the formation of aii and aiii was accompanied by deformation garnet zones ai and aii were formed in the assemblage all biotite epidote plagioclase quartz fluid apatite garnet chlorite muscovite ilmenite sphene magnetite zone aiii in the assemblage garnet muscovite sphene magnetite and zone aiv in the assemblage garnet sphene ilmenite the chemical zonation and microstructures of garnet a indicate two important discontinuities one at the transition between garnet zones ai and aii and a second between zones aii and aiii which correlate with complex zonation shown by epidote and plagioclase these discontinuities may result from polymetamorphic garnet growth during different orogenic cycles affecting the moine supergroup geothermobarometric calculations and gibbs method modelling provide evidence that garnet zone ai grew rapidly during heating from about 550 to 560 c at pressures of about 4 6 kbar in contrast the formation of zone aii was accompanied by nearly isothermal compression from 6 to 8 5 kbar 560 575 c indicating crustal stacking after a certain period of cooling garnet zone aiii grew during renewed heating at p t conditions of about 640 c and pressures between 5 and 9 kbar growth of garnet aiv was accompanied by further temperature rise reaching maximum conditions of about 670 c at 5 kbar

metamorphism of the central anatolian crystalline complex turkey influence of orogen normal collision vs wrench dominated tectonics on p t t paths the central anatolian crystalline complex cacc is a microcontinent in the alpine himalayan belt it has previously been considered as a coherent structural entity but although the entire cacc is comprised of similar rocks primarily metasedimentary rocks and granitoids it consists of at least four tectonic blocks characterized by different p t t paths these blocks are the kirsehir north west akdag north east nigde south and aksaray west massifs the northern massifs experienced thrusting and folding during collision and were slowly exhumed by erosion metamorphic rocks are characterized by clockwise p t paths at moderate p t and local low p high t lp ht overprinting in the highest grade rocks apatite fission track ages are eocene to oligocene 47 32 ma the aksaray block represents the hot shallow mid crust of a late cretaceous early tertiary arc it is dominated by intrusions rare metapelitic rocks record low p 4 kbar regional metamorphism overprinted by lp ht contact metamorphism apatite fission track ages are 50 45 ma the nigde massif is different from the other cacc blocks because it evolved as a core complex in a wrench dominated setting it is characterized by clockwise p t paths at moderate p t followed by widespread lp ht metamorphism apatite fission track ages are miocene 12 9 ma significantly younger than those in the northern massifs nigde rocks resided in the mid crust at a time when the rest of the cacc was at or near the earth s surface variations in p t t and tectonic histories especially timing of exhumation between the northern and southern cacc reflect the difference between head on collision vs mid crustal wrenching

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

ultra high temperature metamorphism in central brazil the barro alto complex the barro alto complex central brazil is a layered mafic ultramafic intrusion which was subjected to granulite facies metamorphism during the neoproterozoic ultra high temperature conditions are recorded by parageneses that occur in some lenses of quartz bearing rock metagranite metapelite and impure quartzite the peak paragenesis consists of spinel quartz cordierite leucosome recording the former presence of melt with quartz in excess which is replaced by either orthopyroxene sillimanite or garnet sillimanite quartz biotite sillimanite garnet symplectites are ubiquitous and indicate reactions between fe mg phases and melt late kyanite porphyroblasts have overgrown these symplectites the direct replacement of spinel quartz cordierite by orthopyroxene sillimanite or garnet sillimanite occurred around the sa invariant point which appears only in a petrogenetic grid with inverted topology the topology inversion occurs at conditions of high oxygen fugacity or due to the presence of zno bearing spinel minimum peak conditions of ultra high temperature metamorphism were calculated as c 980 c and c 7 9 kbar the succession of observed mineral textures can be explained by a near isobaric cooling p t path with a cooling stage occurring between c 980 and 750 c

hot contacts of garnet peridotites in middle upper crustal levels new constraints on the nature of the late variscan high t low p event in the moldanubian central vosges ne france p t paths based on parageneses in the immediate vicinity of former high temperature contact zones between mantle peridotites and granulitic country rocks of the central vosges ne france were derived by applying several conventional thermometers and thermobarometric calculations with an internally consistent dataset the results indicate that former garnet peridotites and garnet spinel peridotites were welded together with crustal rocks at depths corresponding to 1 1 2 gpa the temperature of the crustal rocks was about 650 700 c at this stage whereas values of 1100 c garnet peridotites and 800 900 c garnet spinel peridotites were calculated for the ultramafic rocks after emplacement of the mantle rocks exhumation of the lower crust took place to a depth corresponding to 0 2 0 3 gpa the temperatures of the incorporated peridotite slices were still high 900 1000 c at this stage this is indicated by the presence of high t low p parageneses c 800 c 0 2 0 3 gpa in a small 1 10 m contact aureole around a former garnet peridotite crustal rocks distant to the peridotites equilibrated in the same pressure range at lower temperature 650 700 c high cooling rates 102 103 c ma 1 were calculated for a garnet biotite rock inclusion in the peridotites and for the crustal rocks at the contact by applying garnet biotite diffusion modelling minimum rates of 0 75 7 5 cm a 1 are required for vertical ascent of rock units 30 km vertical distance derived from the crust mantle boundary resulting in a late variscan 340 ma high t low p event

garnet zoning and the identification of equilibrium mineral compositions in high pressure temperature granulites from the moldanubian zone austria a detailed investigation of the compositional variation in garnet has been undertaken in a garnet pyroxene bearing granulite from the high grade gfohl unit moldanubian zone lower austria textural observations together with the interpretation of the preserved garnet chemistry enables the recognition of both prograde core and peak metamorphic garnet mantle growth stages an extremely rare feature in high p t granulite facies rocks initial thermobarometric calculations undertaken across whole garnet zoning profiles show how correct interpretation of a zoning profile is essential if the maximum peak metamorphic p t conditions are to be recovered the effect of retrograde decompression and cooling driven reactions on inclusion and host garnet compositions has also been assessed the results indicate that caution should be exercised when utilizing inclusion and adjacent garnet compositions for the thermobarometric evaluation of peak metamorphic equilibration conditions peak p t conditions were determined by the tweequ thermobarometric method utilizing the core compositions of matrix phases combined with the interpreted high p t garnet mantle composition to give 15 6 kbar and 1090 c consistent with previously determined results for moldanubian granulites similar high p t estimates are also provided by a re evaluation of previously published results for a granulite sample from the same lithological unit using a modified interpretation of garnet and plagioclase compositional data the new estimates presented confirm the previously disputed idea that the gfohl unit underwent a high pressure granulite facies stage and is therefore distinctly different from the underlying tectonostratigraphic units it is emphasized that any interpretation of the peak metamorphic conditions in high grade rocks must be based on detailed petrographic observations combined with a thorough understanding of the co existing equilibrium mineral compositions

preservation of permo triassic low pressure assemblages in the cretaceous high pressure metamorphic saualpe crystalline basement eastern alps austria metapelites and intercalated metapegmatites of the saualpe crystalline basement which forms part of the austroalpine nappe complex in the eastern alps display a polyphase tectonometamorphic history here we focus on the evolution that these rocks underwent prior to cretaceous eo alpine high pressure metamorphism and related penetrative deformation geothermobarometry on coarse grained porphyroclastic parageneses garnet biotite muscovite plagioclase sillimanite quartz which occur as relics in kyanite garnet two mica gneiss yielded 600 c 0 4 gpa results from a corundum bearing lithology suggest that higher temperatures may have been reached in very restricted areas the matrix of these rocks displays intense recrystallization during a pressure dominated metamorphic overprint microstructures and mineral chemistry indicate that this low pressure metamorphism was the first significant metamorphic imprint in these rocks mineral relics in all metapelitic rock types reflect low pressure conditions for this interkinematic crystallization phase the distribution macroscopic and microscopic observations and the mineralogical composition of intercalated metapegmatites point to regionally elevated temperature conditions during their emplacement therefore pegmatite formation is correlated with mineral formation in metapelites sm nd dating of magmatic garnet from the pegmatite gneiss yielded 249 3 ma which is interpreted to represent the age of pegmatite emplacement and low pressure metamorphism in the metapelites since the pegmatites are overprinted by mylonitisation and high pressure metamorphism this permo triassic age also sets an upper age limit to the eclogite facies metamorphic event which affected considerable parts of the saualpe crystalline basement