low to medium pressure variscan metamorphism in galicia nw spain evolution of a kyanite bearing synform and associated bounding antiformal domains

new transfer functions for nutations of a nonrigid earth there are differences between the observed values of nutation and the computed ones based on the international astronomical union iau 1980 adopted nutation series these differences can be expressed in the frequency domain where they may reach several milliarc seconds a level that is too large for practical use this paper aims to resolve part of these differences by computing a new theoretical model accounting for additional geophysical effects a new transfer function is computed based on an earth initially in a nonhydrostatic equilibrium corresponding to the steady state associated with the present mantle convection the mantle mass anomalies are deduced from seismic tomography data and the flow induced boundary deformations are computed from internal loading for an earth made up of a viscous inner core a liquid outer core a viscous mantle and a solid lithosphere in this way a new core mantle boundary cmb flattening is obtained which gives the observed free core nutation fcn period furthermore the global earth dynamical flattening induced by the mass anomalies in the mantle associated with tomography and by the mass anomalies due to the computed boundary deformations is in agreement with the j2 form factor or the observed precession constant in addition to this nonhydrostatic initial state the rheology of the mantle is considered as inelastic the transfer function for nutation is then obtained by numerical integration of motion equations from the earth s center up to the surface to provide a model which is completely self consistent in order to validate our model the transfer function is convolved with new rigid earth nutations ocean corrections are applied and the final results are then compared with the observed nutations or with the international earth rotation service iers nutation series the residuals between our model and the observation are about 3 times smaller than those between the iau 1980 adopted model and the observation however our model still presents residuals above the observational error this is particularly true for the out of phase part of the residuals while the in phase part gives very small residuals improvement of about 1 order of magnitude a further step in this study is a refinement of the modeling of geophysical fluids core ocean and atmosphere

collapse of the thickened variscan crust in the french massif central mont pilat extensional shear zone and st etienne late carboniferous basin abstract a large scale extensional shear zone is described from the mont pilat area in the northeastern part of the french massif central this shear zone is about 2 km thick and is characterized by well developed n dipping foliation and stretching lineations deformation occurred under conditions of retrograde metamorphism from high temperature conditions to greenschist facies it is superimposed on a composite foliation related to the earlier variscan 380 350 ma compressional events associated with southward emplacement of nappes and hp mt metamorphism regional n s lineations and shear criteria observed at a regional scale indicate a northward displacement of the hanging wall during extension large strains locally recorded in thick mylonitic zones suggest that displacement was substantial some tens of kilometres late superimposed extensional brittle deformation and pseudotachylites show that northward displacement on normal faults continued at a shallower depth a large granitic pluton granite du velay intruded late in the the variscan orogeny was associated with extension some small leucogranitic syntectonic melts were emplaced within the shear zone and are strongly deformed geochronological rb sr data on these leucogranite bodies give an age of 320 ma and 40 ar 39 ar dating of synkinematic biotites from gneissose rocks in the shear zone yields a plateau age of 313 ma these data show that extensional ductile deformation and magmatism were still active during the latest late carboniferous thus extension occurred immediately after the well known late palaeozoic collision type compressional tectonics which had significantly thickened the crust we propose that the extensional tectonism described here is due to the gravitational collapse of the initially thick variscan crust the stephanian intracontinental sedimentary basin of st etienne was formed along the hanging wall of the normal shear zone during the late stages of this post orogenic crustal extension

u pb zircon and sm nd model ages of high grade moldanubian metasediments bohemian massif czechoslovakia we report single grain u pb ion microprobe as well as conventional bulk size fraction ages for zircons from 3 metasediment samples of the moldanubian complex bohemian massif one of the largest crystalline complexes of the hercynian foldbelt in europe these are complemented by whole rock sm nd model ages the metasediments are of upper amphibolite to granulite grade and come from the bory massif in moravia nw of brno sample aa 1 and from the varied group aa 2 and monotonous group aa 3 in the ceske budejovice region of sw bohemia

crustal evolution of the ktb drill site from oldest relics to the late hercynian granites the crustal unit penetrated during the german continental deep drilling program ktb the zone of erbendorf vohenstrauss zev comprises an association of metabasites and paragneisses and orthogneisses that underwent high and medium pressure metamorphic cycles during the early palaeozoic in this summary of the structural petrological geochemical and geochronological information from borehole and surface rocks we show that geological models proposed prior to drilling have had to be significantly modified features of the zev such as the dominant nw se trending structures devonian 370 ma medium pressure amphibolite facies metamorphism 0 6 0 8 gpa 720 c and earlier eclogite stage are directly comparable with those of the nearby bohemicum unit in western bohemia intervening units in contrast exhibit ne sw trending structures and carboniferous 315 325 ma low pressure metamorphism all units are cut by predominantly posttectonic granites mostly 320 ma earlier models to explain this contrast by means of a nappe emplacement of the zev in the narrow time interval between the younger regional metamorphism and granite intrusion could not be substantiated because contrary to predictions the same rock association was present in the whole of the drilled 9 1 km and therefore no nappe boundary was drilled instead it is interpreted that shallow crustal levels reached by the zev subsequent to the devonian event shielded most of it from the effects of the carboniferous metamorphism a lack of expected thermal and baric gradients within the drilled metamorphic pile is a result of repeated stacking of an original 3 km depth section in mesozoic times an important result of the geological investigations of the ktb project is the recognition that the present day geometry of the zev is a result of cold shallow level thin skinned tectonics that in the absence of the view into the third dimension offered by the drill hole could not have been accurately predicted from the fossil high grade assemblages and structures seen at the surface

age geodynamic setting and mantle enrichment processes of a k rich intrusion from the meissen massif northern bohemian massif and implications for related occurrences from the mid european hercynian the plutonic complex of the meissen massif northern margin of the bohemian massif comprises dioritic to mainly monzonitic and granitic rocks the diorite to monzonite intrusions show major and trace element patterns typical for shoshonitic series the chemical signatures of less crustally contaminated diorites are similar to arc related shoshonitic rocks derived from continental lithospheric mantle clm sources previously enriched by subduction of altered oceanic crust laser step heating 40ar 39ar analyses on actinolitic to edenitic amphiboles from geographically different occurrences of the monzonitic intrusion yielded concordant plateau ages as well as total gas ages ranging from 329 1 1 4 to 330 4 1 4 ma and from 330 4 2 1 to 330 6 1 8 ma respectively these cooling ages are indistinguishable from sensitive highresolution ion microprobe shrimp 238u 206pb intrusion ages measured on magmatic zircon rims from the monzonite nasdala et al submitted this shows that the monzonite intrusion is probably not related temporally to active subduction because it postdates eclogites of the adjacent saxonian erzgebirge by approximately 20 ma the shoshonitic magmas intruded during strike slip tectonism along the elbe valley zone the enrichment of their mantle sources may be of upper devonian lower carboniferous age or older intrusions of shoshonitic to ultra potassic k rich rocks during the upper visean namurian are widespread in the moldanubian zone based on similar ages and structural relationships a similar post collisional setting to the meissen shoshonitic rocks can be demonstrated most of these occurrences cut high grade nappe units which were subducted during the upper devonian lower carboniferous in contrast to the meissen massif at least the ultra potassic members of the central and the south bohemian batholiths were derived from clm sources enriched by fluids or melts released from subducted oceanic crust and by greater portions of crustal material despite the similar post collisional geodynamic setting of the k rich intrusions different enrichment processes generated mid european hercynian clm sources with heterogeneous major and trace element and isotopic signatures

late cadomian crustal tilting and cambrian transtension in the tepla barrandian unit bohemian massif central european variscides the cadomian basement of the tepla barrandian unit is characterized by a classic barrovian type metamorphism the degree of which increases considerably towards the west reaching amphibolite facies conditions in the domaz lice crystalline complex dcc the number and volume of plutons also increases towards the west the emplacement ages of the te s ovice granite and the mrac nice trondhjemite have been determined at 521 7 2 ma and 523 4 5 ma respectively applying conventional u pb analyses of zircons pervasive high temperature prolate fabrics and north northwest dipping dextral oblique slip shear zones within the mrac nice trondhjemite suggest a synkinematic melt emplacement within a lower cambrian transtensional setting transtension is probably related to early stage rifting that introduced the separation of the tepla barrandian unit as part of armorica from gondwana structural and petrological data of the country rocks show that the barrovian type metamorphism and two deformation stages d1 with unknown kinematics and d2 top to the north shearing are older than the melt emplacement and thus can be attributed to the cadomian orogeny the intrusion depth of both plutons is nearly the same ca 7 km although the degree of barrovian type metamorphism differs significantly within the country rocks this suggests late cadomian eastward tilting of the metamorphic isograd planes the weak post plutonic lower greenschist to subgreenschist facies folding and thrusting result from variscan northwest southeast compression

dehydration melting and the granulite transition in metapelites from southern namaqualand s africa in a prograde amphibolite granulite transition zone in the namaqualand metamorphic complex metapelites show an interbanding of the amphibolite facies association biotite sillimanite quartz with the granulite facies association garnet cordierite k feldspar relict graded bedding shows that compositional banding is of sedimentary origin the garnet cordierite k feldspar gneisses contain quartzofeldspathic segregations surrounding garnets and have more fe rich bulk compositions than the biotite sillimanite schists

extending a thickened crustal bulge toward a new geodynamic evolution model of the paleozoic nw bohemian massif german continental deep drilling site se germany abstract fault bounded tectonic metamorphic complexes assembling the nw bohemian massif around the german continental deep drilling ktb site are seen to be extremely heterogeneous in tectonic and metamorphic histories in current models the different complexes were supposed to reflect a puzzle of small pre devonian microplates and the related collision events supposedly lasted until the carboniferous opposed to these models it will be shown that all the boundaries among the complexes were formed by detachment late in a prolonged overall geodynamic history of a thickened crustal bulge during extensional tectonics and associated thermal events that outlasted the onset of collision in the silurian lower devonian by about 70 80 ma micro structures petrological and geochronological data of individual complexes predominantly preserve the late stages rather than the unbroken record of their tectonometamorphic histories such partial histories strongly different among individual complexes depict diverse snapshots taken at different places in the evolving thickened crustal bulge and at different instants in its overall evolution and do not define different precollisional microplates predominantly p t and deformation episodes after terrane juxtaposition are preserved this article presents an integrated view of the structural geology microscopic fabrics p t data and geochronology of such diverse metamorphic complexes this integrated view provides a new understanding of 1 the tectonic evolution during upper silurian devonian collision of the gondwana derived central european lithosphere with laurussia 2 the postaccretionary events that lasted through the upper carboniferous and 3 the earlier lower ordovician metamorphic and magmatic history which is only locally recorded metamorphic complexes occupying the structurally highest position upper tectonic complexes record devonian and earlier tectonometamorphic and magmatic events after the mid devonian such complexes did not experience any metamorphism the recorded devonian events consist of subduction and exhumation of hp rocks and their exhumation involved thrusting and extensional tectonics upper tectonic complexes comprise fragments of both the plate that was subducted in this period and the overriding plate in the footwall carboniferous extension has brought upper tectonic complexes against metamorphic complexes that essentially record lower and upper carboniferous tectonometamorphic and magmatic events lower tectonic complexes in the lower tectonic complexes such events are 1 consecutive extensional stages that created at least three sets of ductile normal detachment systems intersecting each other and various associated thermal pulses as well as 2 predetachment events that are only recorded as petrologic and structural relics transposed during extension inferred as predetachment events are crustal subduction as well as stacking that outlasted thrusting and exhumation of the upper tectonic complexes in the deeper portion of the thickened crustal bulge represented by the lower tectonic complexes spatial variations of p t t d histories during decompression occurred as a result of continued differential exhumation on the three sets of detachment systems and also from various thermal pulses that have affected different parts of this section during progressive shearing and exhumation to various degrees whereas the lower tectonic complexes of the erzgebirge gneiss dome preserve the record of a lower carboniferous history of hp metamorphism and crustal thickening followed by extension in those of the oberpfalz region ktb site a major upper carboniferous thermal pulse mostly erased the pre upper carboniferous strain fabrics and metamorphic record in the oberpfalz region ongoing extension emplaced mid crustal rocks that pervasively equilibrated in the upper carboniferous at high temperatures and low pressures low p t ratio against rocks not exposed to high temperatures at that time in summary a prolonged postaccretionary history concealed large scale structural relationships linked to crustal subduction and thickening associated with former juxtaposition of gondwana lithosphere to laurussia polyphase crustal extension and strike slip created the variety of different metamorphic tectonic complexes observed in the nw bohemian massif

sensitivity of the free core nutation and the chandler wobble to changes in the interior structure of mars abstract in view of the forthcoming mars missions with seismological and geodetic experiments on board the sensitivity of mars normal modes to interior structure changes is examined the emphasis is put on the chandler wobble cw and the free core nutation fcn as both can play an important role in the nutations and tides of mars the fcn especially is found to have a large potential for inferring properties of the interior structure of mars if observed it will prove that mars contains a liquid core and information about the core radius and density jump at the core mantle boundary cmb can be obtained spheroidal oscillation modes of mars are also shown to provide a powerful and additional constraint on the martian interior

high pressure granulites from the sudetes south west poland evidence of crustal subduction and collisional thickening in the variscan belt two high grade gneissic complexes of the western sudetes the gory sowie block and the nieznik area complex contain small predominantly felsic granulitic inliers with minor cpx bearing intercalations the p t conditions of the granulite facies events and of the subsequent re equilibration are estimated using the ternary feldspar thermometer and the geo calc computer program version twq jan 92 in the gory sowie granulites the peak granulitic event occurred at c 18 20 kbar and 900 c and the late decompressive re equilibration within a range of 4 10 kbar and temperatures decreasing to 600 700 c the latter event is thought to have coincided with the main metamorphic phase in the surrounding gneisses the p t estimates are more scattered in the nieznik granulites but the peak conditions for the granulitic event are estimated at pressure over 22 kbar possibly around 30 kbar and temperature exceeding 900 c the analysed samples from the nieznik area bear no significant evidence of lower pressure re equilibration integrating the thermobarometric data and some age constraints indicates that the gory sowie granulites belong to the early stage type i granulites of the variscan belt c 400 ma old which are interpreted as fragments of continental crustal materials subducted to mantle depths in the earliest stages of the variscan orogeny the nieznik granulites are more problematic they may belong to a younger high p suite c 350 ma old widespread in the southern and eastern parts of the bohemian massif and possibly related to the climax of the variscan continent continent collision

holocene high altitude vegetation dynamics in the pyrenees a pedoanthracology contribution to an interdisciplinary approach abstract using an interdisciplinary methodology based on pedoanthracology palynology and sedimentary charcoals landscape transformation in the pyrenees mountains during the holocene is analyzed with special attention to altitudinal variation in the treeline the data sources were eight soil profiles on a transect at 2000 2600 m a s l and a sedimentary record extracted from a very nearby peat bog at 2247 m a s l the combination of three different proxies permits a more viable and qualitatively complementary data set making it possible to better interpret the vegetation dynamic in this space through the holocene analysis of the data showed that the pyrenees landscape has undergone important changes during this period the changing treeline is a good example there is evidence of the decisive role of fire in the configuration of this landscape finally this study shows that herding and agricultural uses over thousands of years in the study area have had a determining influence on the current configuration of the territory equal to or more important than climatic factors

interior structure and seasonal mass redistribution of mars from radio tracking of mars pathfinder doppler and range measurements to the mars pathfinder lander made using its radio communications system have been combined with similar measurements from the viking landers to estimate improved values of the precession of mars pole of rotation and the variation in mars rotation rate the observed precession of 7576 35 milliarc seconds of angle per year implies a dense core and constrains possible models of interior composition the estimated annual variation in rotation is in good agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps

partially retrograded eclogites of the munchberg massif germany records of a multi stage variscan uplift history in the bohemian massif eclogites with a wide range in bulk composition are present in the munchberg massif part of the variscan basement of the bohemian massif in north east bavaria new analyses of the primary phases garnet omphacite phengite and amphibole as well as the secondary phases clinopyroxene ii various amphiboles biotite phlogopite plagioclase margarite paragonite prehnite and pumpellyite reveal a complex uplift history new discoveries were made of samples with very jadeite rich primary omphacite as well as a secondary omphacite in a symplectite with albite various geothermobarometric techniques together with thermodynamic databases incorporating separately determined activity composition values and experimental data have clustered the minimum conditions for the primary assemblages to the p t range 650 60 c 14 3 1 kbar however jadeite in omphacite kyanite paragonite in phengite and zoisite grossular in garnet kyanite quartz relationships suggests pressures of 25 28 kbar at the same temperatures the fact that the secondary omphacite plagioclase assemblage yields pressures within a few hundred bars of the minimum pressures for the plagioclase free assemblages strongly suggests that the minimum values are serious underestimates zoning inclusion suites and breakdown reactions of primary phases in addition to new minerals formed during uplift define a polyphase metamorphic evolution which from geochronological evidence occurred solely within the variscan cycle the complex breakdown in other bohemian massif eclogites and the distinct variation in their temperatures during uplift suggest a multi stage thrusting model for the regional evolution of the eclogites such an evolution has significance with respect to incorporation of mantle slices into crustal sequences and fluid derivation from successively subducted units possibly driving the breakdown reactions

p t evolution and fluid inclusion characteristics of retrograded eclogites munchberg gneiss complex germany kyanite eclogites occur as part of the munchberger nappe pile in ne bavaria west germany eclogites are overprinted by subsequent amphibolite facies metamorphism the preservation of primary eclogitic textures as well as symplectitic textures are indicative of rapid decompression eclogite formation is estimated to have occurred under conditions of high h2o activities at pressures between 20 and 26 kbar and temperatures ranging between 590 and 660 c as is shown by the coexistence of omphacite jd 50 kyanite zoisite and quartz minimum pressure estimates independent of the water activity range between 9 and 16 kbar at the relevant temperatures detailed studies of fluid inclusion reveal two predominant groups of aqueous brine inclusions high salinity 14 17 wt nacl equiv and low salinity 0 8 wt nacl equiv inclusions fluid compositions of both groups of inclusions yield isochores passing close to the estimated amphibolite facies pt field the compositions of these fluids are in good agreement with fluid compositions considered from mineral equilibria none of the fluid inclusions has densities appropriate for eclogite facies metamorphism but probably reflect later amphibolite facies metamorphism

40ar39ar chronology of variscan tectono metamorphic events in an exhumed crustal nappe the monts du lyonnais complex massif central france abstract the monts du lyonnais metamorphic complex is part of the high grade nappes of the massif central france retrogression of metamorphic conditions occurred synchronously with evolution of deformation from penetrative thrust structures at high t conditions stage p1 2 700 50 c to strike slip ductile shear at lower p t conditions stage p3 t 600 c this evolution distinguishes progressive exhumation and cooling of this previously buried variscan segment in this study 40ar 39ar chronologic investigations are addressed to representative samples of each tectono metamorphic stage associated with the exhumation of the nappe the two mineral generations yield indistinguishable dates of 350 340 ma which are interpreted as post metamorphic cooling ages however the minerals which crystallized during the late intra continental stage p3 yield concordant plateau dates while the minerals which grew during the p1 2 stage and escaped later retrogressive deformation systematically display disturbed age spectra these heterogeneous profiles could result from the presence of a minor excess ar component incorporated at the time of the p3 event when intense deformation took place under decreasing metamorphic temperature and synkinematic granite emplaced along ductile wrench faults this tectono metamorphic event could have been responsible for a local redistribution of ar from the deformed rock volumes into the less or not deformed ones or for a redistribution of ar at the grain scale in the monts du lyonnais complex the effects of intense deformation and dynamic crystallization were probably associated with retrograde cooling to control the contrasting behaviour of the two mineral generations as a regional consequence these radiometric data imply that complete retrogression of the monts du lyonnais complex was achieved 340 ma ago the sharp cluster of ages obtained for the amphiboles muscovites and biotites used in this study suggests relatively rapid cooling at least 50 c ma 1 of the complex after attainment of metamorphic conditions associated with the p3 event the younger values of 325 315 and 250 ma produced by k feldspar and plagioclase respectively may reflect that 1 the metamorphic complex experienced slow cooling at most 10 c ma 1 between 325 and 315 ma ago and 2 a late weak thermal event

chronology of late paleozoic tectonothermal activity in the southeastern bohemian massif austria moldanubian and moravo silesian zones 40ar 39ar mineral age controls abstract new 40ar 39ar hornblende and muscovite ages from the moldanubian and moravian zones of the southeastern bohemian massif indicate rapid cooling associated with continental underplating during early carboniferous plate collision and closure of the moravo silesian foredeep 40ar 39ar ages have been determined for hornblende concentrates from 1 amphibolite from the moldanubian nappe complex including the dobra gneiss rehberg amphibolite and loosdorf complex all part of the variegated unit 2 micaschist structurally overlying the bittesch gneiss and 3 amphibolite within the bittesch gneiss moravian zone the five hornblende concentrates display variably discordant 40ar 39ar age spectra because of contamination with extraneous argon components however 36ar 40ar vs 39ar 40ar isotope correlations are well defined for the five hornblende concentrates mswd the hornblende and muscovite ages are interpreted to date post variscan metamorphic cooling through ca 500 c and ca 400 c respectively no record of pre variscan thermal events is preserved in either the hornblende or muscovite argon systems however the widespread occurrence of extraneous argon components suggest a pre variscan stage of tectonothermal development the near concordancy of the hornblende and muscovite cooling ages suggest relatively rapid cooling through the contrasting argon closure temperatures and indicate that relatively high crustal levels had likely been attained during the early carboniferous

tidally induced surface displacements external potential variations and gravity variations on mars abstract we have used and extended roosbeek s tidal potential for mars to calculate tidal displacements gravity variations and external gravitational potential variations the tides on mars are caused by the sun and to a lesser degree by the natural satellites phobos 8 relative to the sun and deimos 0 08 relative to the sun to determine the reaction of mars to the tidal forcing the love numbers h l and k and the gravimetric factor were calculated for interior models of mars with different state density and radius of the core and for models which include mantle anelasticity the latitude dependence and frequency dependence of the love numbers have been taken explicitly into account the love numbers are about three times smaller than those for the earth and are very sensitive to core changes e g a difference of about 30 is found between a model with a liquid core and an otherwise similar model with a solid core tidal displacements on mars are much smaller than on earth due to the smaller tidal potential but also due to the smaller reaction of mars smaller love numbers for both the tidal diplacement and the tidal external potential perturbations the tidal signal is at the limit of detection and is too small to permit properties of mars s interior to be inferred on the other hand the phobos tidally induced gravity changes which are subdiurnal with typical periods shorter than 12 h can be measured very precisely by the very broad band seismometer with thermal control of the seismological experiment seis of the upcoming netlander mission it is shown that the phobos induced gravity tides could be used to study the martian core

mars and mercury rotation variations from altimetry crossover data feasibility study 1 knowledge of the interior structure of terrestrial planets can be achieved by studying the changes of their rotation and orientation in time we simulate the use of time deviations of altimetry crossover positions to infer information on the nutations of mars and on the librations of mercury the analysis is based on the least squares estimator and uses simulated crossover points the simulations demonstrate that the use of crossover data improves the estimates of the observed libration amplitude and obliquity of mercury and allows detecting the nutations of mars

petrology structure and geotectonic implications of glaucophane bearing eclogites and related rocks from the malpica tuy mt unit galicia northwest spain abstract the malpica tuy mt unit is a narrow band of basement in galicia northwest spain composed of mica schists paragneisses and calc alkaline to peralkaline orthogneisses with minor amounts of metamorphosed basic rocks garnet omphacite glaucophane barroisite rutile phengite paragonite kyanite zoisite developed in eclogites s s and eclogitic impure sandstones garnet phengite rutile zoisite in the calc alkaline orthogeneisses and garnet phengite rutile chloritoid kyanite in the metasediments biotite breakdown in the orthogneisses and related hornfelses produced garnet with development of coronitic textures plagioclase porphyroblasts with aligned inclusions of rutile and phengite are a common feature of many paragneisses the minimum p t conditions for the equilibrium of garnet omphacite parageneses at the peak of the metamorphism were 600 c 12 2 kbar the mineral chemistry of the orthogneisses and metasediments is compatible with these conditions furthermore the structural data also suggest an in situ origin for the eclogites i e the same as the metamorphism of the enclosing rocks the crystalline area surrounding the mt unit is mainly composed of metasediments and anatectic granites the t at the peak of the metamorphism was higher than 700 c the p being of the order of 5 kbar the two domains represent different parts of the hercynian foldbelt tectonically juxtaposed the juxtaposition is the result of complex tangential tectonics three main phases of compressive deformation having been recognized a first stage of subduction of a thinned crust the materials of the mt unit and subsequent obduction development of hydrated minerals in eclogitic rocks with emplacement of these materials over an already metamorphosed crustal area is suggested the mt unit would represent a remnant of a hercynian thrust nappe

on models of mars interior and amplitudes of forced nutations 1 the effects of deviation of mars from its equilibrium state on the flattening of the core mantle boundary abstract in a static approach the effects of deviation of mars from its equilibrium state on the flattening of the core mantle boundary cmb are studied the calculations are performed for a set of interior structure models with 50 and 100 km thick crust and averaged crustal density varying in the range of 2700 3200 kg m 3 which are based on new values for the moment of inertia and the elastic tidal love number k 2 s defined by konopliv et al konopliv a s yoder c f standish e m yuan d n sjorgen w l 2006 a global solution for the mars static and seasonal gravity mars orientation phobos and deimos masses and mars ephemeris icarus 182 23 50 the models differ in density contrast at the crust mantle boundary and the core radius the observational data constrain the radius of a liquid core to be within 1700 1800 km for joint interpretation of gravity and topography data an outer surface of a hydrostatical model is chosen as a reference surface the green s functions or loading factors technique for the case of a single anomalous density wave located at two depth level is used to compute the second degree cmb deformation and then the cmb flattening two types of models have been calculated an elastic model and a model with an elastic lithosphere and weakened layers below it relaxed values of shear modulus the effective shear modulus of the mantle is reduced in comparison with an elastic one and in extreme case it is approaching zero everywhere except the elastic lithosphere non equilibrium state of mars results in three axiality of the core mantle boundary for an elastic case the deformation of cmb leads to the large decrease of the semiaxis b going through the central region of tharsis rise by 660 780 m and the increase of the equatorial semiaxis a by 240 300 m and the polar axis c by 400 490 m tharsis rise plays a constitutive role for the cmb deformation the second degree harmonics in the expansion of non equilibrium part of gravity field and topography are sensitive first of all to the properties of the crust in the tharsis region non hydrostatic contributions decrease the flattening of the cmb by about 5 6 the effect of loading increases when the value of shear modulus decreases by a factor of 10 but as the shear modulus is decreasing up to zero the flattening is approaching its hydrostatic value

rb sr and u pb isotope studies on migmatites from the schwarzwald germany constraints on isotopic resetting during variscan high temperature metamorphism mineral and isotope studies were undertaken on migmatites from the schwarzwald moldanubian zone of the variscan belt the aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre scale migmatite profiles respectively suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation deformation enhanced mass transport rather than by partial melting anatexis the results of rb sr thin slab dating on these profiles indicate that sr isotopes were not completely reset during migmatization no true isochron ages but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87sr 86sr ratios back to various stages in their evolution the coincidence of these rb sr data with u pb ages of monazites from migmatites and non migmatitic gneisses shows that gneisses and migmatites were formed during the same high temperature event in the carboniferous 330 335 ma the observation that high temperature metamorphism failed to equilibrate sr isotopes on the centimetre scale imposes limitations on the use of conventional whole rock isochron techniques in dating migmatites

accretion and exhumation at a variscan active margin recorded in the saxothuringian flysch the saxothuringian flysch basin on the north flank of the central european variscides was fed and eventually overthrust by the northwestern active margin of the tepla barrandian terrane clast spectra mineral composition and isotopic ages of detrital mica and zircon have been analyzed in order to constrain accretion and exhumation of rocks in the orogenic wedge the earliest clastic sediments preserved are of early famennian age ca 370 ma they are exposed immediately to the nw of the suture and belong to the par autochthon of the foreland besides ultramafic ophiolite material these rocks contain clasts derived from early paleozoic continental slope sediments originally deposited at the nw margin of the saxothuringian basin these findings together with the paleogeographic position of the famennian clastics debris on the northwestern passive margin indicate that the saxothuringian narrow ocean had been closed by that time microprobe analyses of detrital hornblendes suggest derivation from the randamphibolit unit now present in the middle part of the saxothuringian allochthon munchberg nappes detrital zircons of metamorphic rocks formed a little earlier ca 380 ma indicate rapid recycling at the tectonic front the middle part of the flysch sequence ca early to middle visean both in the par autochthon and in the allochthon contains abundant clasts of paleozoic rocks derived from the northwestern slope and rise together with debris of cadomian basement 500 ma granitoids and 380 ma early variscan crystalline rocks all of these source rocks were still available in the youngest part of the flysch c middle to late visean but some clasts record in addition accretion of the northwestern shelf our findings permit deduction of minimum rates of tectonic shortening well in excess of 10 30 mm per year and rates of exhumation of ca 3 mm a and possibly more

the metamorphic signature of contemporaneous extension and shortening in the central himalayan orogen data from the nyalam transect southern tibet abstract geological relationships and geochronological data suggest that in miocene time the metamorphic core of the central himalayan orogen was a wedge shaped body bounded below by the n dipping main central thrust system and above the n dipping south tibetan detachment system we infer that synchronous movement on these fault systems expelled the metamorphic core southward toward the indian foreland thereby moderating the extreme topographic gradient at the southern margin of the tibetan plateau reaction textures thermobarometric data and thermodynamic modelling of pelitic schists and gneisses from the nyalam transect in southern tibet 28 n 86 e imply that gravitational collapse of the orogen produced a complex thermal structure in the metamorphic core amphibolite facies metamorphism and anatexis at temperatures of 950 k and depths of at least 30 km accompanied the early stages of displacement on the main central thrust system our findings suggest that the late metamorphic history of these rocks was characterized by high t decompression associated with roughly 15 km of unroofing by movement on the south tibetan detachment system in the middle of the metamorphic core roughly 7 8 km below the basal detachment of the south tibetan system the decompression was essentially isothermal near the base of the metamorphic core roughly 4 6 km above the main central thrust the decompression was accompanied by about 150 k of cooling we attribute the disparity between the p t paths of these two structural levels to cooling of the lower part of the metamorphic core as a consequence of continued and probably accelerated underthrusting of cooler rocks in the footwall of the main central thrust at the same time as movement on the south tibetan detachment system

kinematics of the variscan thrusting in the eastern moldanubicum bohemian massif czechoslovakia evidence from the naměst granulite massif abstract the tectonic history of the nam st granulite massif eastern part of the bohemian massif moldanubian zone czechoslovakia is interpreted in terms of polyphased generally north directed variscan nappe stacking original acid granulites formed during a presumed phase of lithospheric subduction 750 c 11 14 kbar 370 350 ma were converted into ht mylonites during the dominant deformation phase d 1 as a consequence of complex thrust wrench processes related to intra moldanubian deep crustal stacking 700 c 9 6 kbar 350 330 ma bringing granulites and the surrounding gfohl gneiss on top of the moldanubian nappe sequence this phase was followed by a northeastward superposition of the already stacked moldanubian nappe over the moravian zone phases d 2 d 3 650 400 c 5 3 kbar 335 325 ma which also marginally affected the cadomian basement of the brunovistulicum the variscan tectonic history was terminated by a namurian to lower permian phase of sinistral strike slip movements along nne ssw trending faults

thermobarometry and geotectonic significance of high pressure granulites examples from the moldanubian zone of the bohemian massif in lower austria

geological constraints on the paleozoic tectonic evolution of tectonostratigraphic terranes in the iberian massif abstract the presence of oceanic paleozoic sequences in the iberian variscan fold belt is used to identify and separate suspected exotic terranes from a reference iberian autochthon terrane which constitutes the greater part of it in this paper the relevant data characterizing the pre accretionary evolution of the paleozoic iberian terranes are presented as well as the available evidence concerning the accretionary process itself emphasis is placed on the analysis of the sedimentary igneous and structural expression of the major events which affected the iberian terranes before during and after their amalgamation the main conclusions of such an analysis may be summarized as follows 1 a recognition of rift and passive margin stages in all the iberian massif terranes during the early paleozoic 2 b late paleozoic accretion of the exotic terranes to the iberian autochthon via a long and complex process variscan orogeny which involved initial subduction underneath the latter and eventual obduction followed by oblique collision of a promontory the iberian autochthon northwestern margin with a northwestern continental block this latter process could account for the large scale crustal imbrication shown by the northern branch of the orogen coeval with predominant strike slip faulting in the southern branch as well as with the formation of the typical arcuate shape of this orogenic belt major present uncertainties relate to the palinspastic provenance of continental suspect terranes and their correlation with similar units in other circum atlantic paleozoic orogens a discussion and speculations on this subject are dealt with in the final section of this paper

on models of mars interior and amplitudes of forced nutations 2 the effects of liquid core and mantle elasticity abstract the numerical modeling of mars forced nutation of the real mars model with a radially heterogeneous compressible self gravitating liquid core and elastic mantle is performed effects of three axiality of mars figure are taken into account to compute values for the periods of free core nutation fcn and the amplitudes of forced nutations the effects of the liquid core for different models are of the order of few percents for the prograde semi annual component and of the order of 10 15 for the semi annual retrograde component the absolute values of these effects are of the order of 5 20 ms of arc mas and 1 3 mas respectively taking into account that the modern accuracy of vlbi measurements for the case of the earth is of the order of 0 02 mas we see that important results about mars internal structure may be obtained even if the accuracy of mars nutational measurements 1 2 order of magnitude less than accuracy for the earth the effects of the shear stress relaxation during long time intervals are studied the corrections to the nutational amplitudes for prograde semi annual component are between 8 93 and 9 8 for retrograde semi annual component are between 4 81 and 8 2 ms of arc and the period of free core nutation is varied in the limits between 257 2 and 295 8 earth s solar days the differences exceed significantly the errors of mars nutational components measurements and consequently these measurements can give new important information about martian mantle rheology the possibilities of inferring properties of the interior structure of mars based on the measurements of its rotation are discussed

thermobarometry and granite genesis the hercynian low p high t velay anatectic dome french massif central the velay dome french massif central offers a quasi continuous section across an anatectic domain comprising low to high grade schists gneisses and granites two main tectonometamorphic events and their related generation of granitic material were recognized in addition to a major barrrovian tangential event d2 attributed to intracontinental collision tectonics i a medium to low p high t event d3 which gave rise to migmatites and syntectonic monzonitic granites and granodiorites and ii a widespread melting event d4 which led to the generation of migmatities the velay granite and post anatectic granites thermobarometry on samples collected from both the metamorphic envelope and the granitic core distinguishes two distinct geotherms i a first associated with the d3 event characterized by p 5 kbar t 750 c and water present melting biotite remains stable which led to large scale migmatization but minor amount of granites ii a second associated with the d4 event and characterized by vapour absent melting p 4 5 kbar t 760 850 c which gave rise to the velay granites and late migmatitic granites the temperature increase during the d4 event is attributed to the intrusion of hot mafic magmas within the crust the time integrated features of the different granitic rocks in the velay dome can be directly related to ah2o in the source region and illustrate the progressive dehydration of a middle to lower crustal segment over 60 ma

geochronology and geochemistry of eclogites from the marianske lazně complex czech republic implications for variscan orogenesis the marianske lazn complex mlc is located in the bohemian massif along the north western margin of the tepla barrandian microplate and consists of metagabbro amphibolite and eclogite with subordinate amounts of serpentinite felsic gneiss and calcsilicate rocks the mlc is interpreted as a metaophiolite complex that marks the suture zone between the saxothuringian rocks to the north west and the tepla barrandian microplate to the south east sm nd geochronology of garnet omphacite pairs from two eclogite samples yields ages of 377 7 and 367 4 ma samples of eclogite and amphibolite do not define a whole rock sm nd isochron even though there is a large range in sm nd ratio implying that the suite of samples may not be cogenetic eclogites do not have correlated nd values and initial 87sr 86sr ratios five of the eight eclogite samples have high nd values 10 2 to 7 1 consistent with derivation from a morb like source but variable 87sr 86sr ratios 0 7033 to 0 7059 which probably reflect hydrothermal seawater alteration three other eclogite samples have lower nd values 5 4 to 0 8 and widely variable 87sr 86sr ratios 0 7033 to 0 7096 such low nd values are inconsistent with derivation from a morb source and may reflect a subduction or oceanic island basalt component in their source the mlc is an important petrotectonic element in the bohemian massif providing evidence for cambro ordovician formation of oceanic crust and interaction with seawater late devonian frasnian famennian high and medium pressure metamorphism related to closure of a saxothuringian ocean basin early carboniferous visean thrusting of the tepla terrane over saxothuringian rocks and late visean extension

zircon dating of north bohemian granulites czech republic further evidence for the lower carboniferous high pressure event in the bohemian massif u pb zircon and rutile multigrain ages and 207pb 206pb zircon evaporation ages are reported from high pressure felsic and metapelitic granulites from northern bohemia czech republic the granulites in contrast to those from other occurrences in the bohemian massif do not show evidence of successive ht mplp overprints multigrain size fractions of nearly spherical multifaceted metamorphic zircons from three samples are slightly discordant and yield a u pb concordia intercept age of 348 10 ma whereas single zircon evaporation of two samples resulted in 207pb 206pb ages of 339 1 5 and 339 1 4 ma respectively a rutile fraction from one sample has a u pb concordia intercept age of 346 14 ma all ages are identical within error and a mean age of 342 5 ma was adopted to reflect the peak of hp metamorphism because rutile has a lower closing temperature for the u pb isotopic system than zircon the results and the p t data imply rapid uplift and cooling after peak metamorphism the above age is identical to ages for high grade metamorphism reported from the southern bohemian massif and the granulite massif in saxony it can be speculated that all these granulites were part of the same lower crustal unit in early carboniferous being separated later due to crustal stacking and subsequent late variscan orogenic collapse

thermobarometry diffusion modelling and cooling rates of crustal garnet peridotites two examples from the moldanubian zone of the bohemian massif abstract different origins for crustal garnet peridotites are illustrated by two variscan bodies in adjacent tectonically juxtaposed terranes in the moldanubicum of the bohemian massif eastern moravia the nove dvory garnet peridotite contains lenses of eclogite and is allochthonous and allofacial with respect to surrounding gfohl gneiss the mohelno spinel garnet peridotite is devoid of eclogite and has concordant contacts with surrounding felsic granulite the bulk of the mohelno body is spinel peridotite and garnet occurs only along its margins where it has formed at the expense of spinel thermobarometry of mineral cores from garnet bearing assemblages yields values for nove dvory from 1195 c 54 6 kbar to 970 c 41 8 kbar and for mohelno from 1265 c 27 9 kbar to 1070 c 23 4 kbar the compositional zoning profiles in garnets at both localities are matched closely by diffusion modelling in which bilinear cooling rates are utilized at nove dvory initial cooling rates of 50 200 c ma are followed by slower rates of 10 50 c ma in contrast at mohelno an extremely rapid initial cooling rate of 1 c year was followed by one of 500 c ma an idealized tectonic model is proposed for the emplacement of the mohelno peridotite to account for its cooling history the predicted garnet zoning profiles that result from conductive cooling agree closely with the observed zoning profiles both peridotites were derived from the upper mantle the nove dvory body was emplaced from a deep fault zone into the crust as garnet peridotite and the mohelno body was emplaced as a hot slab of spinel peridotite in which garnet formed only along contacts as the body cooled into the garnet stability field

eclogites in the french palaeozoic orogen geodynamic significance abstract eclogites are widespread in the devonian internal zone of the french palaeozoic orogen they occur in different tectonic settings either in high pressure low temperature or in high pressure high temperature environments they are tectonically incorporated into several major allochthonous units as demonstrated either by their blastomylonitic texture or by their being in evident disequilibrium with their country rocks the protoliths of the presently well identified eclogite bearing series present different typical associations depending on their present location the igneous series include within plate basalts normal and transitional morbs and even calc alkaline rocks they were erupted mostly during the palaeozoic although they sometimes contain inherited precambrian zircons further some of them may be remnants of old precambrian oceanic crust most of the eclogitic parageneses were generated during the earliest silurian tectonometamorphic climax either in low temperature or in high temperature conditions later they followed various retrograde courses in still geographically distinct low temperature or high temperature associations the basic rocks in the leptynolitic amphibolitic complex and particularly the eclogites thus provide sufficiently clear evidence to support a new geodynamic scenario implying one or several subordinate narrow tensional zones in a thinned but well developed continental crust rather than in a true oceanic domain

post collisional variscan lamprophyres black forest germany 40ar 39ar phlogopite dating nd pb sr isotope and trace element characteristics abstract subsequent to high pressure and temperature metamorphism of the axial zone of the variscan foldbelt in central europe at ca 340 to 330 ma formation of lamprophyre dikes during transtensional tectonics may be viewed as the beginning of the post collisional stage of the orogeny we report the results of 40 ar 39 ar mica dating major and trace element data and isotope compositions for lamprophyre and rhyodacite samples from the southern black forest the chemical compositions of these rocks shed light on the upper mantle and crust at the end of the variscan orogeny 40 ar 39 ar plateau ages for four phlogopite biotite separates from lamprophyres indicate emplacement at 332 to 314 ma this event coincides with melting of the crust as indicated by 40 ar 39 ar biotite plateau ages of ca 332 ma for rhyodacite dikes which are probably related to coeval undeformed granites incompatible trace element patterns of the lamprophyre samples reveal the characteristics of evolved continental crust and are interpreted as evidence for melting of sediment in a subduction modified mantle nd sr and pb isotope compositions indicate an enriched mantle source with end values of 1 5 to 6 8 which is similar to variscan crust significant contamination of the lamprophyric melts by variscan crust can be ruled out as mantle derived phlogopite phenocrysts have similar end values as in the whole rock samples we propose that the isotope compositions and incompatible trace element characteristics of the lamprophyres were predominantly inherited from melted sediment the isotope compositions of variscan lamprophyres from western europe suggest that enriched upper mantle was only partly delaminated when ascending hot mantle triggered melting of the lower crust as has been invoked for the origin of post collisional granites the isotope compositions of tertiary basalts and mantle xenoliths indicate a depleted upper mantle under western europe implying that the enriched variscan material was efficiently removed and mixed into the convecting mantle

computation of mars transfer functions for nutations tides and surface loading abstract mars transfer functions for nutations tides and surface loading are computed for different models in order to study the influence of the physics of the interior on the planet s response to external forcing if the core is liquid there is a resonance at the free core nutation fcn period which must be taken into account the fcn period depends on the density of the core and consequently on the density jump at the core mantle boundary cmb and on the dimensions of the core the responses of mars forced by the solar gravitational attraction involve frequencies which could be very close to the fcn the observation of their amplitudes can in that case give us information about whether the core is liquid or not about its dimensions as well as about the density jump at the cmb we therefore consider several models for the interior structure of mars involving different normal mode frequencies and compute the transfer functions for nutations tides and loading as a function of the forcing frequency we show that the amplitudes of the semi annual tri annual and quadri annual nutations could be amplified by several ten percent or even several hundred percent by the fcn resonance depending on the fcn eigenfrequency value here annual means one martian year the same holds for the second degree diurnal tides and loading effects the impact of the core radius density and state on the body and load love numbers is analysed body and low degree load love numbers h and k can change by up to 25 for variations in the core radius of 200 km or for a change in the core state liquid solid the corresponding variations in the tidal gravimetric factor and the loading green s function are about 10 times smaller high degree load love numbers are more sensitive to the upper mantle rheology

martian precession and rotation from viking lander range data the spatial orientation of the martian pole of rotation and axial rotation parameters have been determined at a midpoint in the viking epoch january 1 1980 the mean obliquity e and node angles are e 25 1894 0 0001 35 4796 0 0002 2 the mean precession rate is o 7 83 0 30 arc sec yr 1 the corresponding moment estimate is c mre2 0 355 0 015 and covers two extreme theoretical estimates seasonal annual and semiannual variations in mars rotation angle have also been observed and are 279 100 and 311 100 milliarc second of angle mas respectively after correcting for a general relativity effect a simple model has been constructed for the main contribution involving seasonal mass exchange between the ice caps and atmosphere where the air pressure at the viking 1 lander site is a proxy for the global ice cap air pressure histories the annual term is about 190 mas smaller and differs in phase by 30 compared to the model prediction the semiannual term is 100 mas larger and also differs in phase by 30 compared to the model a combination of tidally driven rotation changes zonal winds polar motion and ice cap model deficiencies may account for any discrepancy the upcoming pathfinder lander and mars global surveyor missions carry ranging transponders which can dramatically improve our knowledge of mars interior through precise determination of the precession rate and detection of core and tidal effects we advocate that plans be developed for a coordinated campaign of simultaneous ranging and doppler tracking to each transponder

glaucophane bearing assemblage overprinted by greenschist facies metamorphism in the variscan kaczawa complex sudetes poland an early palaeozoic ordovician metamudstone sequence near wojcieszow kaczawa mts western sudetes poland contains numerous metabasite sills up to 50 m thick these subvolcanic rocks are of within plate alkali basalt type primary igneous phases in the metabasites clinopyroxene salite and kaersutite are veined and partly replaced by complex metamorphic mineral assemblages particularly the kaersutite is corroded and rimmed by zoned sodic sodic calcic and calcic amphiboles the matrix is composed of actinolite pycnochlorite albite an 0 5 epidote ps 27 33 titanite calcite opaques and occasionally biotite phengite and stilpnomelane the sodic amphiboles are glaucophane to crossite in composition with nab from 1 9 to 1 6 they are rimmed successively by sodic calcic and calcic amphiboles with compositions ranging from magnesioferri winchite to actinolite no compositions between nab 0 92 and nab 1 56 have been ascertained the textures may be interpreted as representing a greenschist facies overprint on an earlier blueschist or blueschist greenschist transitional assemblage the presence of glaucophane and no traces of a jadeitic pyroxene quartz association indicate pressures between 6 and 12 kbar during the high pressure episode temperature is difficult to assess in this metamorphic event the replacement of glaucophane by actinolite chlorite albite with associated epidote allows restriction of the upper pressure limit of the greenschist recrystallization to 8 kbar between 350 and 450 c the mineral assemblage representing the greenschist episode suggests the p t conditions of the high pressure part of the chlorite or lower biotite zone the latest metamorphic recrystallization under the greenschist facies may have taken place in the visean

variscan oceans ages origins and geodynamic implications inferred from geochemical and radiometric data abstract a review of the magmatic associations providing evidence for the existence of extensional regimes during the palaeozoic evolution of variscan europe is presented the available geochronological data allow recognition of two major rifting events one in the early ordovician and the other in the middle late devonian scarce relicts of ophiolitic complexes indicate that both extensional episodes reached a true ocean spreading stage it is suggested that the variscan belt resulted from a complex two stage collision process through successive suturing in the silurian and the early carboniferous of these oceanic domains the superposition of two distinct opening closure cycles involving geographically separate oceanic basins may partly account for the unusual width of the variscan orogen

the interior structure of mars implications from snc meteorites two end member models of mars present interior structure are presented the first model is optimized to satisfy the geochemical data derived from the snc meteorites in terms of the bulk chondritic ratio fe si 1 71 while the second model is optimized to satisfy the most probable maximum value c 0 366 x m p r p 2 of the polar moment of inertia factor hydrostatic equilibrium and stationary heat transfer are assumed and the basic differential equations for the mechanical and thermal structure are solved numerically together with an isothermal murnaghan birch type equation of state truncated in eulerian strain at forth order we obtain the radial distribution of mass hydrostatic pressure gravity temperature and heat flow density along with the corresponding density stratification viscosity profiles and the global seismic velocity structure of model mars the first model being consistent with the geochemical requirement produces c 0 357 x m p r p 2 whereas the second model commensurate with the geophysical constraint gives fe si 1 35 the calculated central pressure is about 40 gpa in both models and the central temperature is in the 2000 to 2200 k range the model calculations suggest a fe ni fes core a little less than one half of the planetary radius in size surrounded by a silicate mantle subdivided into lower spinel and upper olivine layers and overlain by a 100 to 250 km thick basaltic crust and a surface heatflow density of 25 to 30 mw m 2 in both models the pressure in the mantle is not sufficient for the spinel to perovskite transition to occur the present thermal lithosphere is estimated to be about 500 km thick and to be subdivided into a 300 km thick outermost rheological lithosphere and an underlying thermal boundary layer of mantle convection given the core sulfur content of 14 wt as derived from snc meteorites the martian core is found to be entirely molten implying the nonoperation of a self sustained dynamo due to the absence of sufficiently vigorous convection

k ar geochronology of different tectonic units at the northwestern margin of the bohemian massif abstract the polymetamorphic moldanubian mo of the northeasthern margin of the bohemian massif has been thrust to the north onto the mainly paleozoic sedimentary saxothuringian of the fichtelgebirge fg these two units have undergone polyphase deformation and the last regional event to affect both units was a low pressure metamorphism in which temperatures decreased towards the north in contrast the nappe units of the erbendorf vohenstrauss zone zev and the erbendorf greenschist zone egz which partly cover the border of the moldanubian and the saxothuringian and the munchberg nappe pile mm which lies on the saxothuringian were in parts subjected to a late medium pressure metamorphic event the zev the egz the mo and the fg are intruded by late carboniferous granites conventional k ar analyses mainly of hornblendes and muscovites from the autochthonous fg and mo the units beneath the nappes have yielded exclusively carboniferous dates the oldest dates point to a regional cooling of the rocks which outcrop at the present day surface at about 330 320 ma i e at the early late carboniferous boundary the late carboniferous cooling history was largely governed by the thermal influence of the post kinematic granites 320 295 ma especially in the fg and the northern mo the high grade metamorphic rocks in the western part of the zev and in the upper three nappes of the mm mostly yield dates around 380 ma i e early devonian the results show a relatively wide scatter moreover biotites frequently appear to be older than the coexisting muscovites both observations indicate that the rocks underwent a later thermal influence whether some groups of older dates e g 400 ma are due to excess argon or to inherited argon is still open to discussion slightly scattered muscovite dates around 366 ma were obtained for the prasinite phyllite series one of the lower nappes of the mm a single hornblende from the egz gave the same age these two nappes have therefore probably been affected by a late devonian thermal and or tectonic event the muscovite dates obtained from the paleozoic bavarian lithofacies the lowermost nappe of the mm and the hornblende dates from the eastern part of the zev are indistinguishable from those of the autochthonous units fg and mo

hydrostatic interfaces in bodies with nonhydrostatic lithospheres below the lithospheres of the terrestrial planets dwarf planets and moons density interfaces adjust over geologic time to align with surfaces of constant gravitational potential it is well known that the shape of such hydrostatic surfaces is controlled by the pseudo rotational potential tidal potential and the induced potential of nonspherical density interfaces in the body when a lithosphere is present however additional gravitational terms must be considered that arise from for example surface relief and crustal thickness variations a first order formalism is presented for calculating the shape of hydrostatic density interfaces beneath the lithosphere when the gravity field and surface shape of the body are known using an arbitrary discretized density profile the shapes are obtained by solving a simple matrix equation as examples lithospheric gravity anomalies account for about 10 of the relief along hydrostatic interfaces in mars whereas for the moon the lithospheric gravity is the dominant contributor to the core shape spherical harmonic degree 1 mass anomalies in the lithosphere generate degree 1 relief along the core mantle boundary and for mars and the moon the core is offset from the center of mass of the body by about 90 m the moments of inertia of the core of these bodies are also misaligned with respect to the principal moments of the entire body an improved crustal thickness map of mars is constructed that accounts for gravity anomalies beneath the lithosphere and the consequences of core relief on the martian free core nutation are quantified plain language summary the shapes of the solid planets and moons are largely hydrostatic and are determined by their rotation rate if the body has gravity anomalies that arise from within a rigid lithosphere these will act to perturb the shape of hydrostatic density interfaces beneath the lithosphere such as the core mantle boundary we present a method to compute the shape of density interfaces beneath the lithosphere when the gravity field of the body is known as examples of our technique we compute the shape of the core mantle boundary for mars and the moon both of which are shown to have important contributions that arise from the lithosphere we also generate a new crustal thickness map that accounts for gravity anomalies generated beneath the lithosphere

geochemical and geochronological cross section of the deep variscan crust the cabo ortegal high pressure nappe northwestern spain the high pressure rocks of the cabo ortegal nappe and related massifs are represented by several tectonometamorphic units which underwent separate histories before regional overthrusting and amphibolite facies recrystallization at 380 ma the occurrence of final cooling is recorded by 40ar 39ar and rb sr mica ages of up to 350 ma u pb zircon dating and sm nd and rb sr isotope data together with ree and major and trace element geochemistry provide constraints on the timing of earlier tectonothermal events and the nature of the protoliths the earliest tectonothermal event occurred at 490 480 ma and corresponds to the emplacement of lree enriched magmas of probable calc alkaline affinity and their metamorphism in the granulite facies this occurred at approximately the same time as the eclogite facies metamorphism of morb like protholiths associated with basic to intermediate granulites together this suggests formation of syn accretion granulites in an active margin setting a second high grade metamorphic event is recorded at 420 ma in metasedimentary formations associated with eclogite like assemblages garnet omphacite plagioclase this event is possibly related to a collisional plate tectonic setting in a back arc basin the age and origin of the associated ultrabasic rocks remains unclear but a late pyroxenite vein has yielded an emplacement age of 390 ma

tectonometamorphic evolution of the bohemian massif evidence from high pressure metamorphic rocks the variscan orogenic belt of which the bohemian massif is a part is typically recognized for its characteristic low pressure high temperature metamorphism and a large volume of granites however there are also bodies of high pressure rocks eclogites garnet peridotites and high pressure granulites which are small in size but widely distributed throughtout the massif initially the high pressure rocks were considered to be relicts of a much older orogenic event but the increasing data derived from isotopic and geochronological investigations show that many of these rocks have palaeozoic protoliths metamorphic ages from the high pressure rocks define no single event instead a number of discrete clusters of ages are found between about 430 ma and the time of the dominant low pressure event at around 320 330 ma

rates of grain boundary diffusion through enstatite and forsterite reaction rims the growth rates of enstatite rims produced by reaction of fo92 and sio2 were determined at 250 1500 mpa and 900 1100 c for a wide range of water contents growth rates were also determined for forsterite rims between mgo and mg2si2o6 and between mgo and sio2 rim growth rates are parabolic indicating diffusion controlled growth of the polycrystalline rims which are composed of 2 m diameter grains rim growth rates were used to calculate the product of the grain boundary diffusion coefficient d a times the effective grain boundary thickness assuming in turn that mgo sio2 and mg2si 1 are the diffusing components coupled diffusion of a cation and oxygen or interdiffusion of mg and si the values for d mgo d and d for enstatite at 1000 c and 700 mpa confining pressure with about 0 1 wt water are about five times larger than the corresponding d a values for samples initially vacuum dried at 250 c most of the increase in d a occurs with the first 0 1 wt water the activation energy for diffusion through the enstatite rims 1100 950 c is 162 30 kj mole the diffusion rate through enstatite rims is essentially unchanged for confining pressures from 210 1400 mpa but the nucleation rate is greatly reduced at low confining pressure for 1 0 wt water present and limits the conditions at which rim growth can be measured the corresponding values for d a through forsterite rims are essentially identical for the two forsterite producing reactions when 0 1 wt water is added and similar to the d a values for enstatite at the same conditions the d a values for forsterite are 28 times larger for samples starting with 0 1 wt water compared to samples that were first vacuum dried thus water enhances these grain boundary diffusion rates by a factor of 5 30 depending on the mineralogy but the total range in d a is only slightly more than an order of magnitude for as wide a range of water contents as expected for most crustal conditions

garnet zoning and reaction textures in overprinted eclogites bohemian massif european variscides a record of their thermal history during exhumation eclogites from different parts of the variscan basement of the bohemian massif show a variation in temperatures recorded at peak pressures as well as during subsequent exhumation these differences are reflected in the extent of modification of pre syn and post eclogite facies garnet compositions and by the types of reactions taking place at garnet rims munchberg massif eclogites formed at conditions of 600 650 c 20 kbar were mainly overprinted in the amphibolite facies field and contain garnets with an old homogeneous core and often well preserved idiomorphic growth zoning to mg rich rims in the marianske lazn complex the eclogite facies stage 640 715 c 15 kbar many eclogites show well developed granulite facies overprints with widespread orthopyroxene growth in garnet and omphacite domains spinel and or sapphirine after kyanite and in some cases even a low pressure high temperature overprint that produced fe rich olivine the latter rocks clearly endured higher temperatures during breakdown but remarkably strong growth zoning and sharp overgrowth features are preserved in some cases diffusion modeling shows that the preservation of zoning in garnet of rocks that have experienced granulite facies temperatures is only possible if the time spent at these conditions is short 1 ma this time scale is inconsistent with a smooth p t t path as expected from thermal modeling for erosion or extension driven exhumation and implies that these variscan rocks experienced short lived thermal events during their exhumation history