microstructural deformation record of an orogen parallel extension in the vepor unit west carpathians abstract deformation microstructures of quartzo feldspathic rocks have been used to analyse the orogen parallel stretching of the vepor unit in the west carpathians during cretaceous convergence this process occurs contemporaneously with the burial of the vepor basement related to the overthrusting palaeozoic volcano sedimentary sequences of the gemer unit the microstructures develop along a metamorphic gradient indicating an increase of pressure and temperature towards the structural footwall the recrystallization of quartz occurs in the field of subgrain rotation recrystallization sgr while the plagioclase and k feldspar disintegrate into a neocrystallized muscovite albite matrix palaeopiezometry of the recrystallized quartz in conjunction with p t estimates yield strain rates of 9 10 12 to 6 10 14 s 1 depending on temperature 380 480 c and choice of piezometer and flow law calibration strain analysis of the recrystallized quartz aggregates and quartz texture analysis indicate an overprint of the variscan magmatic and high grade fabrics by a cretaceous plane strain deformation resulting in vertical shortening and horizontal orogen parallel east west stretching spatial distribution and conflicting sense of shear of the asymmetrical quartz lattice preferred orientation patterns indicate that the large scale pure shear deformation of the vepor unit is locally accommodated by simple shear zones observed metamorphic gradients across the vepor unit are interpreted to result from later large scale folding and heterogeneous exhumation of the orogen parallel deformation fabric

very low grade metamorphism of sedimentary rocks of the meliata unit western carpathians slovakia implications of phyllosilicate characteristics the meliata unit represents a melange like accretionary wedge containing blueschist facies tectonic blocks and slices in a triassic and jurassic sedimentary matrix the blueschist facies rocks are tectonic remnants of the subducted parts of the meliata hallstatt branch of the tethys the phyllosilicate assemblages in very low grade metapelites represent metastable disequilibrium stages which the assemblages have reached during reaction progress therefore temperature and pressure values of low t metamorphism of the sedimentary series and the late stages of decompressional cooling of blueschist facies rocks obtained by phyllosilicate crystallinity chlorite thermometric and white k mica geobarometric methods can be regarded as semiquantitative estimates however results of chlorite white mica thermobarometry suggest that local equilibrium was approached at a microscopic scale for deciphering the age relations of prograde and retrograde events k ar isotope geochronological methods were applied the sedimentary series and related basalts of the meliata unit experienced high t anchizonal prograde regional metamorphism the temperature and pressure of which can vary between ca 280 and 350 c and ca 2 5 and 5 kbar white k mica b geobarometry suggests possible minimal pressures of ca 1 5 to 3 kbar the mylonitic retrogression of blueschist facies phyllites is characterised by 340 c and 4 kbar minimal p the low t prograde metamorphism was synchronous with the retrograde metamorphism of the blueschists the ages of these two events may be between ca 150 and 120 ma culminating most probably at around 140 145 ma thus the upper jurassic lowermost cretaceous very low grade metamorphism of the meliata unit is younger than the subduction related 160 155 ma blueschist facies event and definitely older than the cretaceous 100 90 ma metamorphism of the footwall gemer palaeozoic

jurassic strike slip versus subduction in the eastern alps late jurassic formations of the northern calcareous alps nca contain ample evidence of synsedimentary tectonics in the form of elongate basins filled with turbidites debris flows and slumps clasts are derived from the mesozoic of the nca they commonly measure tens of metres in diameter and occasionally form kilometre size bodies these sedimentologic observations and the presumed evidence of late jurassic high pressure metamorphism recently led to the hypothesis of a south dipping jurassic subduction zone with accretionary wedge in the southern parts of the nca we present new 40ar 39ar dates from the location of the postulated high pressure metamorphism that bracket the age of this crystallization not earlier than 114 120 ma the event is therefore part of the well documented mid cretaceous metamorphism of the austro alpine domain thus there is currently no evidence of late jurassic high pressure metamorphism to support the subduction hypothesis the sediment record of the late jurassic deformation in the nca including the formation of local thrust sheets is no conclusive evidence for subduction all these phenomena are perfectly compatible with synsedimentary strike slip tectonics large strike slip fault zones with restraining and releasing bends and associated flower structures and pull apart basins are a perfectly viable alternative to the subduction model for the late jurassic history of the nca however in contrast to the eastern alps transect where arguments for a jurassic subduction are missing a glaucophane bearing jurassic high pressure metamorphism in the meliatic realm of the west carpathians is well documented there the high pressure low temperature slices occur between the gemeric unit and the silica nappe system including the aggtelek rudabanya units which corresponds in facies with the juvavic units in the southern part of the nca to solve the contrasting palaeogeographic reconstructions we propose that the upper jurassic left lateral strike slip system proposed here for the eastern alps continued eastwards and caused the eastward displacement of the silica units into the meliatic accretionary wedge

detrital zircon u pb geochronology of pennsylvanian permian sandstones from the turnaicum and meliaticum western carpathians slovakia provenance and tectonic implications the blueschist bearing borka nappe regarded as a part of the meliaticum unit s l and the turnaicum unit in its hanging wall were thrusted together to the north on the inner western carpathians basement during the orogenic events of the late jurassic early cretaceous a new u pb sensitive high resolution ion microprobe shrimp magmatic as well as detrital zircon ages were used to constrain provenance and paleogeography the detrital zircon age spectrum of the studied metasediments contains mainly ages of the ediacaran cryogenian 550 720 ma and tonian stenian 0 9 1 1 ga which correspond to the pan african belt and saharan metacraton subordinate archean ages were likely derived from the saharan metacraton of north gondwana 1 7 2 2 and 2 5 2 7 ga the 273 2 ma zircon age of a metarhyolite along with the youngest detrital zircon of 265 4 ma from the associated metasediments specify the maximum depositional age of the bucina fm from the borka nappe to the guadalupian the rhyolite olistoliths from the middle late jurassic meliaticum olistostrome yielded the latest cambrian earliest ordovician 488 6 ma and middle ordovician 465 ma zircon ages this is consistent with the u pb zircon ages from the foot walling southern gemericum basement metavolcanites which are therefore regarded as a potential source the obtained zircon ages confirm the provenance from the southern gemericum basement and its permian envelope for the meliaticum borka nappe and turnaicum sedimentary embayment

metamorphic evolution of the susunai metabasites in southern sakhalin russian republic the susunai complex of southeast sakhalin represents a subduction related accretionary complex of pelitic and basic rocks two stages of metamorphism are recognized 1 a local low p t event characterized by si poor calcic amphiboles 2 a regional high p t event characterized by pumpellyite actinolite epidote sodic amphibole sodic pyroxene stilpnomelane and aragonite the major mineral assemblages of the high p t susunai metabasites contain pumpellyite epidote actinolite chlorite epidote actinolite chlorite epidote na amphibole na pyroxene chlorite haematite the na amphibole is commonly magnesioriebeckite the na pyroxene is jadeite poor aegirine to aegirine augite application of empirically and experimentally based thermobarometers suggests peak conditions of t 250 300c p 4 7 6 kbar textural relationships in susunai metabasite samples and a petrogenetic grid calculated for the fe3 rich basaltic system suggest that pressure and temperature increased during prograde metamorphism

experimental investigations of blueschist greenschist transition equilibria pressure dependence ofal2o3 contents in sodic amphiboles a new geobarometer

geochronological evidence for the alpine tectono thermal evolution of the veporic unit western carpathians slovakia abstract tectono thermal evolution of the veporic unit was revealed by multiple geochronological methods including 87rb 86sr on muscovite and biotite zircon and apatite fission track and apatite u th he analysis based on the new data the following alpine tectono thermal stages can be distinguished the eo alpine cretaceous nappe stacking 135 95 ma resulted in burial of the veporic unit beneath the northward overthrusting gemeric unit and overlying jurassic meliata accretionary wedge during this process the veporic unit reached metamorphic peak of greenschist to amphibolite facies accompanied by orogen parallel flow in its lower and middle crust the subsequent evolution of this crust is associated with two distinct exhumation mechanisms related to collision with the northerly tatric fatric basement the first mechanism 90 80 ma is associated with internal subhorizontal shortening of the veporic unit reflected by large scale upright folding and heterogeneous exhumation of the veporic lower crust in the cores of crustal scale antiforms this led to juxtaposition of the higher and lower grade parts of basement all cooled down to 350 c by 80 ma the second mechanism is associated with the overthrusting of the veporic unit over the attenuated fatric crust this led to a passive en block exhumation of the veporic crust from 350 c to 60 c between 80 and 55 ma followed by erosion 55 35 ma the erosion processes resulted in formation of planation surface before the late eocene transgression after erosion and planation a new sedimentary cycle of the central carpathian palaeogene basin was deposited with the sedimentary strata thickness of 1 5 2 0 km 21 17 ma the early to middle miocene is characterised by destruction tectonic disintegration and erosion of this basin 20 13 ma and formation of the neogene vepor stratovolcano 13 ma the final shaping of the area has been linked to erosional processes of the volcanic structure since the late sarmatian with accelerated processes during the plio quaternary

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

cretaceous collision and indentation in the west carpathians view based on structural analysis and numerical modeling 1 a model of indentation of a rigid promontory into weak metasedimentary rocks during cretaceous convergence is suggested for tectonic evolution of southern part of west carpathians an early arcuate cleavage fan has developed in front of northward moving southern rigid basement block the interaction of the moving indenter with western stationary basement promontory is responsible for development of the boundary parallel shear zone along which the main southern indenter is shifted to the east this results in development of a new steep transpressional cleavage overprinting the early fabric eastward displacement of the southern indenter causes the development of a thrust zone parallel to the margin of the eastern stationary promontory a proposed numerical model of the deformation of a thin viscous sheet in front of oval rigid indenter reliably simulates the development of the observed deformation pattern modeled discrete partitioning between the western promontory and the indenting block fully agrees with the observed secondary cleavage associated with the transpressional shear zone our numerical model interconnects this complex kinematic frame with finite strain pattern which was to date possible only for simple boundary conditions in addition the model explains the polyphase cleavage patterns in terms of complex shapes of promontories and changes in movements of indenting blocks

continuity and episodicity in the early alpine tectonic evolution of the western carpathians how large scale processes are expressed by the orogenic architecture and rock record data

petrological and kar and40ar39ar age constraints for the tectonothermal evolution of the high pressure meliata unit western carpathians slovakia abstract the meliata high pressure unit exposed in the southern part of the western carpathians consists of four groups of rocks which are characterized by different lithologies and metamorphic histories 1 the most common are triassic marbles intercalated with metabasalts and glaucophane bearing phyllites phengite from metabasalts and phyllites record k ar and40ar 39ar plateau ages of 152 155 ma which are interpreted to date the high pressure metamorphism 2 blueschist facies mafic rocks and subordinate glaucophane bearing micaschists devoid of marbles which contain relic low si muscovite and newly formed high si phengite the40ar 39ar data obtained for the micas indicate palaeozoic ages of 375 380 ma for the early amphibolite facies muscovite and a 250 ma age for the secondary blueschist facies phengite 3 glaucophane free phyllites and phengite quartzite with low si and high si micas respectively textural features indicate a polyphase evolution characterized by a greenschist facies metamorphism followed by a blueschist facies overprint the high si micas provide evidence for an early middle jurassic age 172 ma of the high pressure metamorphism 4 amphibolite facies slices and blocks overprinted by blueschist facies metamorphism represent old basement rocks regarding the differences in lithologies metamorphic conditions and radiometric ages of high pressure micas older age for continental vs younger age for oceanic rocks subduction of a continental wedge prior to that of oceanic crust can be assumed this interpretation is based also on palaeogeographical reconstruction of the mesozoic western tethys between the apulian promontory and the tisza bihor continental block

quantitative analysis of seismicity in iran we use historical and recent major earthquakes and gps geodetic data to compute seismic strain rate geodetic slip deficit static stress drop the parameters of the magnitude frequency distribution and geodetic strain rate in the iranian plateau to identify seismically mature fault segments and regions our analysis suggests that 11 fault segments are in the mature stage of the earthquake cycle with the possibility of generating major earthquakes these faults primarily are located in the north and the east of iran four seismically mature regions in southern iran with the potential for damaging strong earthquakes are also identified we also delineate four additional fault segments in iran that can generate major earthquakes without robust clues to their maturity the most important fault segment in this study is the strike slip system near the capital city of tehran with the potential to cause more than one million fatalities

calculated mineral equilibria in the greenschist blueschist eclogite facies in na 2 o feo mgo al 2 o 3 sio 2 h 2 o the new greatly expanded internally consistent dataset of holland and powell includes thermodynamic data for a wide range of mineral end members in common rock forming minerals in particular including femg 1 substitutions in glaucophane garnet chloritoid and carpholite and femg 1 and mgsial 1al 1 substitutions in talc and chlorite moreover we have the uncertainties and correlations for these data with the data we have calculated the full pressure temperature phase diagram for the system na2o feo mgo al2o3 sio2 h2o nfmash for quartz or coesite and h2o in excess in the range 300 800 c and 5 50 kbars by solving the set of non linear equations formed by the equilibrium relationships for an independent set of equations between the end members in an assemblage in nfmash the compositions of the minerals and pt can be calculated thus the changes in mgsial 1al 1 along nmash reactions and fesial 1al 1 along nfash reactions are calculated and the changes in femg 1 and mgsial 1al 1 along nfmash reactions are calculated from this information it is straightforward to generate pt diagrams for specific rock compositions mineral assemblages and mineral compositional changes in the phase diagram are discussed in relation to greenschist blueschist and eclogite facies assemblages in metapelitic rocks it is found that the correspondence between the predictions of the phase diagrams and the observations on rocks is remarkably good when semiquantitative extensions of the phase diagram to include ca mgfe 1 nasica 1al 1 fe3 al 1 and kna 1 substitutions are taken into account the agreement is essentially complete

alpine reworking of ordovician protoliths in the western carpathians geochronological and geochemical data on the muran gneiss complex slovakia abstract magmatic protoliths of ordovician age have been identified in the metamorphic rocks of the muran gneiss complex veporic unit central western carpathians vapor digestion single zircon u pb dating yields an intrusion age of 464 35 ma upper intercept for the granite protolith a lower intercept age of 88 40 ma records amphibolite facies metamorphic overprint in the cretaceous during the alpine orogeny geochemical and isotopic data suggest crustal origin of the orthogneiss nd initial are between 2 6 and 5 0 and t dm nd between 1 3 and 1 5 ga two step approach 87 sr 86 sr initial ratios vary between 0 7247 and 0 7120 and a steep ree pattern further constrains the crustal affinity of these rocks associated amphibolite bodies have nd initial values of 6 5 87 sr 86 sr initial ratio of 0 7017 and a flat ree pattern they are interpreted as morb derived metabasites whole rock pb isotope analyses define a linear array in a 206 pb 204 pb vs 207 pb 204 pb diagram with an age of ca 134 ma consistent with intense alpine metamorphism and deformation these basement rocks of the central western carpathians are interpreted as ordovician magmatic rocks intruded at an active margin of gondwana they represent the eastern prolongation of cambro ordovician units of the european variscides which were part of the peri gondwana superterrane and accreted to laurussia during the variscan orogeny variscan metamorphic overprint is not recorded by the isotopic data of the muran gneiss complex alpine metamorphism is the most dominant overprint

molecular dynamics simulation of structures bulk moduli and volume thermal expansivities of silicate liquids in the system cao mgo al2o3 sio2 materials in the system cao mgo al2o3 sio2 are important constituents of the earth s lower crust and mantle silicate liquids in this geophysically important system have been studied using molecular dynamics md simulation with an empirical interatomic potential cmas94 md simulations are quite satisfactory in reproducing well the observed structure and pressure volume temperature equation of state parameters of molten enstatite mgsio3 wollastonite casio3 diopside camgsi2o6 and anorthite caal2si2o8 at 1900 k and 0 gpa however the md simulated bulk modulus of molten forsterite mg2sio4 at 2300 k and 0 gpa k0 18 0 6 gpa is found to be much smaller than the value k0 60 gpa at similar temperature and pressure conditions estimated previously based on melting curve analyses of forsterite in an attempt to investigate the possible occurrence of the density inversion between magmatic liquids and residual crystals in the upper mantle conditions as proposed by stolper et al 1981 we have further applied the md technique with the cmas94 potential to the diopside system at 1900 k as an example and have found that the density inversion between crystal and liquid in this system actually occurs at approximately 11 gpa

phase petrology and p t conditions of mafic blueschists from the meliata unit west carpathians slovakia blueschists occurring as layers in calcite marbles of the meliata unit occur along the so called roznava tectonic line situated in the southern part of the gemericum slovakia mineral assemblages and compositions from seven blueschists localities and one occurrence of amphibolite facies rocks overprinted by blueschist metamorphism were investigated the most common minerals in the blueschists are blue amphibole epidote and albite some fe2 and al rich rocks also contain garnet and chloritoid respectively na pyroxene with a maximum 50 jadeite component was also found the blue amphiboles correspond mostly to crossite and also to glaucophane and ferroglaucophane in some samples almandine and spessartine rich garnet has very low mgo content 3 wt the si content in phengite ranges between 3 3 and 3 5 pfu calculated on the basis of 11 oxygens the zoning patterns of blue amphibole garnet and chloritoid suggest their formation during a prograde stage of metamorphism the p t conditions of metamorphism are estimated to be about 380 460 c and 10 13 kbar pressures of 7 5 8 5 kbar and temperatures of 350 370 c were obtained for some actinolite and aegirine rich rocks apart from chlorite other mafic minerals formed during retrograde metamorphism are biotite and occasionally also actinolite

the effect of whole rock mno content on the stability of garnet in pelitic schists during metamorphism garnet bearing mineral assemblages are commonly observed in pelitic schists regionally metamorphosed to upper greenschist and amphibolite facies conditions modelling of thermodynamic data for minerals in the system na2o k2o feo mgo al2o3 sio2 h2o however predicts that garnet should be observed only in rocks of a narrow range of very high fe mg bulk compositions traditionally the nearly ubiquitous presence of garnet in medium to high grade pelitic schists is attributed qualitatively to the stabilizing effect of mno based on the observed strong partitioning of mno into garnet relative to other minerals in order to quantify the dependence of garnet stability on whole rock mno content we have calculated mineral stabilities for pelitic rocks in the system mno na2o k2o feo mgo al2o3 sio2 h2o for a moderate range of mno contents from a set of non linear equations that specify mass balance and chemical equilibrium among minerals and fluid the model pelitic system includes quartz muscovite albite pyrophyllite chlorite chloritoid biotite garnet staurolite cordierite andalusite kyanite sillimanite k feldspar and h2o fluid in the mno free system garnet is restricted to high fe mg bulk compositions and commonly observed mineral assemblages such as garnet chlorite and garnet kyanite are not predicted at any pressure and temperature in bulk compositions with xmn mn fe mg mn 0 01 however the predicted garnet bearing mineral assemblages are the same as the sequence of prograde mineral assemblages typically observed in regional metamorphic terranes temperatures predicted for the first appearance of garnet in model pelitic schist are also strongly dependent on whole rock mno content the small mno contents of normal pelitic schists xmn 0 01 0 04 are both sufficient and necessary to account for the observed stability of garnet

calibration and testing of an empirical chloritoid chlorite mg fe exchange thermometer and thermodynamic data for daphnite a compilation of literature data on the fe mg composition of coexisting chlorite and chloritoid from metapelites metamorphosed at various p t conditions shows that the logarithm of the fe mg partitioning lnkd varies linearly with the inverse of temperature from about 2 4 at 300 c to about 1 3 at 600 c in contrast no trend was observed with pressure and the molar volumes of mg and fe chlorite end members suggest that the pressure dependence of lnkd is not significant therefore the chloritoid chlorite mg fe exchange reaction is a potential thermometer and has been empirically calibrated using the analyses of 112 chloritoid chlorite pairs from 28 different localities temperatures estimated using the chl cld thermometer were checked against independent estimates for 20 samples not involved in the calibration beni mzala window morocco and the results are in fair agreement with independent temperature estimates however the analytical uncertainties and errors are too large to obtain reliable temperature estimates for extremely mg rich or fe rich compositions the chl cld thermometer is unreliable at xmg cld 0 8 at 700 c and xmg cld 0 9 at 300 c using the results of the empirical calibration we calculated new thermodynamic data for daphnite implementing these data it becomes possible to estimate t and p conditions of metamorphism for the invariant chlorite chloritoid quartz aluminosilicate assemblage that is widespread in low grade metapelites these estimates appear to be relevant only in the stability field of kyanite whereas the uncertainties on the calculated pressure conditions are very large in the stability field of kaolinite and pyrophyllite

40ar 39ar dating of the inner carpathians variscan basement and alpine mylonitic overprinting abstract the 40ar 39ar dating method has been applied to mylonitic rocks from the carpathian mountains these are variscan metamorphic and magmatic rocks that were overprinted during the alpine orogeny the inner western carpathians are conventionally described as a nappe pile formed by northward movement and then subjected to intense strike slip and normal faulting resulting in the formation of mylonitic rocks precise stratigraphie ages provide clear constraints for the geodynamic interpretation related to the succession of alpine events such as the pre gosauian phase during the turonian 90 ma the 40ar 39ar method allows to define the age of the ancient variscan basement and the ages of the alpine overprinting in the high and low tatras mineral ages of around 340 350 ma are yielded by gneisses micaschists and amphibolites providing a younger limit for the variscan metamorphism the emplacement cooling of the variscan granites is defined between 305 and 335 ma these rocks are overprinted by several alpine tectonothermal events the major events are dated at 65 and 86 88 ma during which the mylonites were generated an older event around 140 ma earlier defined by the rb sr method is now confirmed by the 40ar 39ar method dating of phengites extracted from high pressure metamorphic triassic rocks from the kosice area yields new data for the age of this event at 155 ma