sequence of thrusting within a thick skinned tectonic wedge evidence from40ar 39ar and rb sr ages from the austroalpine nappe complex of the eastern alps the sequence of thrusting within a regional scale alpine thick skinned tectonic wedge has been constrained by rb sr and 40ar 39ar dating of whole rock constituent white mica and biotite from structural units of the austroalpine nappe complex eastern alps austria preservation of variscan and pre variscan isotopic signatures in pre alpine basement units indicates a non penetrative metamorphic alpine overprint alpine nappe assembly and accompanying ductile deformation occurred during maintenance of lower greenschist facies metamorphic conditions c 300 450 c analyses from greenschist facies metamorphic mylonites and penetratively ductile deformed cover sequences display decreasing 40ar 39ar plateau ages structurally downward thrusting and accompanied ductile deformation commenced at c 100 90 ma in the uppermost structural levels footwall fault propagation effected internal deformation and out of sequence thrusting within intermediate structural levels at c 95 80 ma this was contemporaneous wit

tectonic wedging blueschist metamorphism and exposure of blueschists are they compatible tectonic wedging is currently deforming rocks along the westernmarginofthecentralvalleyofcalifornia structuralrelations in the strata of the mesozoic great valley group fore arc basin indicatethatearlierphasesofwedgingwerecoevalwithsubduction and accretion of the franciscan complex to the west the presentday geometry of tectonic wedging is incompatible with blueschist metamorphism in the franciscan complex because the detachment for the wedge system would have prevented the transport of accretionary wedge materials to great depth we propose a sequence of tectonic events that reconciles these tectonic processes franciscan subduction and metamorphism began at 165 ma and great valley group deposition began in the tithonian shortening affected great valley group rocks in the hauterivian barremian and may havecoincidedwithagapinblueschistmetamorphisminthefranciscan major uplift of franciscan blueschist relative to the unmetamorphosed great valley group rocks began in the albian cenomanian this uplift was accommodated along an east dipping extensional fault system between the franciscan complex and the structurally overlying coast range ophiolite and great valley group movement on this fault system caused the western side of thefore arcbasintosubside resultinginuninterrupteddeposition ofgreatvalleygroupsedimentsfromthecenomaniantothecampanian maastrichtian the youngest exposed blueschists in the franciscan were metamorphosed at 80 90 ma uplift of blueschist relativetogreatvalleygrouprocksmusthavebeencompleteprior todevelopmentofthepresentstyleofeast vergenttectonicwedging this style of deformation probably began between the maastrichtian and paleocene resulting in exhumation and deformation of bothfranciscanandgreatvalleygrouprocks thedevelopmentof wedging was coincident in part with the shallowing of subduction dip and voluminous frontal accretion of the coastal belt of the franciscan

anthropogenic origin of siliceous scoria droplets from pleistocene and holocene archaeological sites in northern syria abstract siliceous scoria droplets measuring from 1 to 10 mm from one late pleistocene and four early holocene archaeological sites in northern syria are compared to similar droplets previously suggested to be the result of a cosmic impact at the onset of the younger dryas global cooling event the findings demonstrate that the presence of siliceous scoria droplets are independent of age and thus are not specific to the beginning of the younger dryas occurrences have not been reported from natural deposits but are instead associated with buildings destroyed by fire and thus appear to be restricted to archaeological sites we therefore conclude that melting of building earth in ancient settlements can occur during fires reaching modest temperatures there is no evidence to suggest that siliceous scoria droplets result from very high temperature melting of soil and are the result of a cosmic event

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

how many oceans meliata vardar and pindos oceans in mesozoic alpine paleogeography the timing of rifting and subduction in the meliata vardar and pindos zones of the hellenic dinaric carpathian region indicates that they cannot be considered remnants of a single ocean basin in contrast to several recently published mesozoic paleogeographies sea floor spreading in the meliata zone culminated in middle triassic ladinian time and ceased in the late triassic and subduction occurred from this time until late jurassic closure in contrast sea floor spreading in the vardar zone began in early jurassic time and culminated in the middle jurassic and subduction occurred from latest jurassic time in the pindos zone sea floor spreading was initiated in the early triassic with late jurassic and early tertiary subduction

age of amphibolitic metamorphism in the ophiolitic unit of the morais allochthon portugal implications for early hercynian orogenesis in the iberian massif structurally lower portions of the allochthonous morais complex are comprised of an ophiolitic unit exposed in two contrasting structural units separated by a ductile thrust fault the lower unit is dominated by variably foliated amphibolite whereas the upper unit is largely comprised of metaperidotite and metagabbro most of the ophiolitic unit has recrystallized synkinematically under amphibolite facies metamorphic conditions c 500 c and 5 kbar amphiboles formed during this metamorphism are typically magnesio hornblende an amphibole concentrate from the lower structural unit records a 39 ar 40 ar plateau age of 397 3 4 ma an amphibole concentrate from the upper structural unit displays an internally discordant 39 ar 40 ar age spectrum corresponding to a total gas age of 431 1 27 3 ma gas fractions evolved from each amphibole concentrate at intermediate and high experimental temperatures are characterized by similar apparent k ca ratios and yield well defined 36 ar 40 ar v 39 ar 40 ar isotope correlations which result in similar ages of 384 2 5 2 and 392 4 7 3 ma these are considered to be more reliable than the plateau ages and are interpreted as dating the last cooling through those temperatures required for intracrystalline retention of argon within constituent amphibole grains the associated tectonothermal event represented a first stage of hercynian orogenesis in the iberian massif it was probably related to oceanic closure and associated obduction of granulitic eclogitic massifs which at present structurally overlie the ophiolitic unit

alpine and pacific styles of phanerozoic mountain building subduction zone petrogenesis of continental crust a broad continuum exists between two distinct end member types of mountain building alpine type orogenic belts develop during subduction of an ocean basin between two continental blocks resulting in collision they are characterized by an imbricate sequence of oceanward verging nappes some alpine belts exhibit superimposed late stage backthrusting sediments are chiefly platform carbonates and siliciclastics in some cases associated with minor amounts of bimodal volcanics pre existing granitic gneisses and related continental rocks constitute an autochthonous parautochthonous basement metamorphism of deeply subducted portions of the orogen ranges from relatively high pressure hp to ultrahigh pressure uhp calcalkaline volcanic plutonic rocks are rare and have peraluminous s type bulk compositions in contrast pacific type orogens develop within and landward from long sustained oceanic subduction zones they consist of an outboard oceanic trench accretionary prism and an inboard continental margin island arc the oceanic assemblage consists of first cycle in part melanged volcaniclastics and minor but widespread cherts deep water carbonates intimately mixed with disaggregated ophiolites the section recrystallized under hp conditions recumbent fold vergence is oceanward a massive slightly older to coeval calcalkaline arc is sited landward from the trench complex on the stable non subducted plate it consists of abundant dominantly intermediate metaluminous i type volcanics resting on old crust both assemblages are thrown into open folds intruded by comagmatic i type granitoids and metamorphosed locally to regionally under high t low p conditions in the subduction channel of collisional and outboard circumpacific terranes combined extension above and subduction below allows buoyancy driven ascent of ductile thin aspect ratio slices of hp uhp complexes to midcrustal levels where most closely approached neutral buoyancy exposure of rising sheets caused by erosion and gravitational collapse results in moderate amounts of sedimentary debris because exhumed sialic slivers are of modest volume at massive sialic buildups associated with convergent plate cusps syntaxes tectonic aneurysms may help transport hp uhp complexes from mid to upper crustal levels the closure of relatively small ocean basins that typify many intracratonic suture zones provides only limited production of intermediate and silicic melts so volcanic plutonic belts are poorly developed in alpine orogens compared with circumpacific convergent plate junctions generation of a calcalkaline arc mainly depends on volatile evolution at the depth of magma generation phase equilibrium studies show that under typical subduction zone p t trajectories clinoamphibole ca al hydrous silicates constitute the major hydroxyl bearing phases in deep seated metamorphic rocks of morb composition other hydrous minerals are of minor abundance ca and na clinoamphiboles dehydrate at pressures of above approximately 2 gpa but low temperature devolatilization may be delayed by pressure overstepping thus metabasaltic blueschists and amphibolites expel h2o at melt generation depths and commonly achieve stable eclogitic assemblages partly serpentinized mantle beneath the oceanic crust dehydrates at roughly comparable conditions for reasonable subduction zone geothermal gradients however white micas biotites remain stable to pressures 3 gpa accordingly attending descent to depths of 100 km mica rich quartzofeldspathic lithologies that constitute much of the continental crust fail to evolve substantial amounts of h2o and transform incompletely to stable eclogite facies assemblages underflow of amphibolitized oceanic lithosphere thus generates most of the deep seated volatile flux and the consequent partial melting to produce the calcalkaline suite along and above a subduction zone where large volumes of micaceous intermediate and felsic crustal materials are carried down to great depths volatile flux severely diminishes thus continental collision in general does not produce a volcanic plutonic arc whereas in contrast the long continued contemporaneous underflow of oceanic lithosphere does

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

late jurassic blueschist facies pebbles from the western carpathian orogenic wedge and paleostructural implications for western tethys evolution in spite of the absence of ophiolitic slices at the surface some traces of the lost tethys ocean are recorded along the pieniny klippen belt pkb a narrow decollement thrust system sutured at the transpressive boundary between the outer and inner carpathians the enigmatic precollisional evolution of western carpathians can be deciphered from some late albian to campanian flysch conglomerates which display chrome spinel grains ophiolitic detritus and pebbles of blueschist facies tholeiitic metabasalts yielding a 40ar 39ar plateau age of 155 4 0 6 ma other detrital components are represented by extrabasinal pebbles of limestones arc volcanics and igneous to metamorphic basement rocks from southern sources our results suggest a markedly northward extension of the sublongitudinal triassic vardar meliata ocean and its subduction since the late middle jurassic supposedly balanced westward by coeval spreading in the ligurian piedmont basin of the apennine western alpine tethys a lateral kinematic connection between these diachronous and roughly parallel tethys branches was provided on the north by a left lateral east west trending shear zone running from the swiss austrian penninic domain to the northern carpathians this reconstruction replaces the classic model of two paired north penninic and south penninic oceanic basins and eastern homologues with the brianconnais hochstegen and czorstin microcontinents in between the late jurassic early cretaceous evolution of the carpathian active margin was characterized by subduction metamorphism and accretion of a wide orogenic wedge in this time the shallowing to deeply subsiding basins inferred from facies analyses on the sedimentary units of the pkb were likely floored by individual sections of the growing wedge later some exhuming blueschist ophiolitic units of the wedge were uplifted to the surface and functioned in the albian campanian as an exotic ridge supplying clasts to the forearc basin finally the colliding wedge became a cryptic paleostructure when since the latest cretaceous it disappeared beneath the inner carpathian orogenic lid and was incorporated within the eastward moving infrastructure of the carpathian orocline

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

flow characteristics of large eruption triggered debris flows at snow clad volcanoes constraints for debris flow models abstract theoretical modelling is not yet adequate to predict the behavior of debris flows which can be an extremely hazardous hydrologic process commonly associated with volcanic eruptions particularly at snow clad stratovolcanoes to provide a realistic basis for modelling the behavior of large 1000 m3 s debris flows this paper summarizes kinematic volumetric and hydraulic characteristics of ten large historic volcanic debris flows from four different volcanoes although debris flows larger than these are known to have occurred in the past the ten summarized here define a practical upper range in magnitude of more typical flows to be considered for future hazard prediction peak flow velocities of the ten debris flows studied were indirectly measured to be between about 5 and 20 m s on gradients of 0 005 to 0 25 m m but locally they were as great as 40 m s hydraulic average depths were as great as 25 m but were more commonly between 5 and 15 m in channels up to 400 m wide computed peak discharges volumetric flow rates were as high as 105 m3 s and total volumes were as much as 108 m3 total flow volumes increased by as much as four times in relatively steep channels as eroded sediment was incorporated into the debris flows flows generally achieved supercritical flow and deposited minimal volumes of sediment on gradients steeper than 0 02 m m subcritical flow and active deposition predominated on gradients less than 0 01 m m although flows travelled tens of kilometers on such low gradients while laying down deposits total distances travelled as debris flows were as far as 120 km

polyhalite microfabrics in an alpine evaporite melange hallstatt eastern alps in the hallstatt salt mine austria polyhalite rocks occur in 0 5 1 m thick and several metre long tectonic lenses within the protocataclasite to protomylonite matrix of the alpine haselgebirge fm thin section analysis of hallstatt polyhalites reveals various fabric types similar to metamorphic rocks of crust forming minerals e g quartz and feldspar polyhalite microfabrics from hallstatt include 1 polyhalite mylonites 2 metamorphic reaction fabrics 3 vein filling fibrous polyhalite and 4 cavity filling polyhalite the polyhalite mylonites contain a wide range of shear fabrics commonly known in mylonitic quartzo feldspathic shear zones within the ductile crust and developed from a more coarse grained precursor rock the mylonites are partly overprinted by recrystallised statically grown polyhalite grains metamorphic reaction fabrics of polyhalite fibres between blodite or astrakhanite na2mg so4 2 4h2o and anhydrite have also been found according to previous reports blodite may occur primarily as nodules or intergrown with loweite reaction fabrics may have formed by exsolution re crystallisation parallel growth or replacement this fabric type was only found in one sample in relation with the decomposition of blodite at ca 61 c in the presence of halite or slightly above testifying therefore a late stage prograde fabric significantly younger than the main polyhalite formation

extension in compressional orogenic belts the eastern alps extension in the eastern alps encompasses the following 1 extension accompanying simple shear crustal stacking subhorizontal stretching occurs along flat lying foliations and regionally consistent stretching lineations with associated high strains on a local scale stretching results from extrusion of ductile sediments squeezed between rigid basement blocks basement blocks during thrust sheet imbrication the overall geometric effect is crustal thickening 2 classical extensional tectonics extension first occurs as a consequence of accretion and underthrusting of continental and oceanic material and represents gravitational adjustment of an unstable orogenic wedge extension then occurs as a consequence of terminal continental collision and is accommodated by lateral extrusion of crustal of crustal blocks the overall geometric effect is crustal thinning extension is generally oriented subparallel to the strike of the orogen

sedimentology and event timing of a catastrophic volcaniclastic mass flow volcan hudson southern chile eruption of volcan hudson aisen region southern chile on 12 august 1971 melted up to 80 of ice within the 9 km wide hudson caldera rapid mobilisation of abundant fluvio glacial sediment within the adjacent huemules valley led to the generation of a catastrophic mass flow which swept westwards along the valley eventually entering the fjord some 40 km downstream the mass flow developing from one source and being unaffected by tributary input was characterised by three events within the flood hydrograph 1 a precessional flood possibly linked to breakage of an early formed dammed lake 2 a main mass flow which varied in its rheological behaviour from plug flow to hyperconcentrated flow and 3 a recessional flood at the tail of the main flow which diluted towards a concentrated streamflow the main debris flow displayed characteristics of pulsing internal segregation density stratification significant downstream sediment assimilation cohesive frictional freezing with ensuing fluidisation and development of an advancing runout phase consideration of these sedimentary characteristics and spatial temporal flow transformations are used to propose a schematic model of event timing within this catastrophic volcaniclastic flow

low temperature constraints on the alpine thermal evolution of the western carpathian basement rock complexes abstract the cretaceous to palaeogene alpine exhumation of previously buried variscan basements is recorded in the southern portion of the western carpathians in the gemeric and veporic units the meso cenozoic collisional processes resulted in basement exhumation of the tatric unit from palaeogene to neogene times according to zircon and apatite fission track data the gemeric unit an uppermost thick skinned thrust sheet cooled from depth levels of 10 up to 2 5 km temperature interval of 250 60 c about 88 64 ma ago after the collapse of overlying meliata tur a silica mesozoic accretionary prism the middle and lower thick skinned thrust sheets veporic and tatric units cooled from the depths of 10 up to 2 5 km 110 40 ma ago the process was controlled by unroofing of footwall from beneath the gemeric unit about 50 20 ma ago the internal zone of tatric unit gradually exhumed to depth of

mechanisms of blueschist creation and preservation in an a type subduction zone mount olympos region greece deformation and metamorphism in the mount olympos region greece are the result of subduction of continental crust a type subduction during the alpine orogeny new structural and petrologic data from this region provide insight into the creation of low geothermal gradients in a type subduction zones and the preservation of blueschist facies assemblages early convergent deformation was accompanied by greenschist amphibolite facies metamorphism blueschist facies mineral assemblages overprinted higher grade assemblages during large scale episodic shortening that occurred during and after continental collision prehnite pumpellyite facies assemblages are postkinematic with respect to contractional fabrics but predate a prolonged period of extension that was not accompanied by metamorphism under plating and extension permitted unroofing and preservation of the blueschists with no over printing by greenschist facies assemblages

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

bypassing and diachronous deposition from density currents evidence from a giant regressive bed form in the poris ignimbrite tenerife canary islands exceptional longitudinal exposure through an ignimbrite sheet on the southern flanks of las canadas volcano tenerife canary islands reveals a giant regressive bed form 520 m long it comprises sourceward dipping diffuse lenses 50 m long of massive and diffuse bedded lapilli tuff its architectural relationships indicate that at any one moment in time deposition was restricted to an 50 m long longitudinal depositional zone bounded both upslope and downslope by extensive bypassing zones the regressive architecture shows that the zone of deposition gradually migrated sourceward as the current passed nonpersistent scours indicate that the current was locally and momentarily erosive although at many locations there is little evidence for substantial erosion or deposition and most of the pyroclastic load seems to have entirely bypassed subaerial slopes to enter the atlantic ocean 20 km from the source the ignimbrite is diachronous and any single vertical section through it represents only a short phase of the current9s protracted depositional history similarly protracted and complex flow histories elsewhere may be easily overlooked at typical field exposures of ignimbrites turbidites and lahar deposits leading to significantly underestimated flow durations and volumes

architectural analysis of a volcaniclastic jokulhlaup deposit southern iceland sedimentary evidence for supercritical flow the 1918 eruption of the glacially capped katla volcano southern iceland generated a violent jokulhlaup or glacial outburst flood inundating a large area of m rdalssandur the proglacial outwash plain where it deposited ca 1 km3 of volcaniclastic sediment the character of the 1918 jokulhlaup is contentious having been variously categorized as a turbulent water flow a hyperconcentrated flow or as a debris flow based on localized outcrop analysis in this study outcrop based architectural analyses of the 1918 deposits reveal the presence of lenticular and tabular bedsets associated with deposition from quasi stationary antidunes and down current migrating antidunes and from regular based bedsets associated with transient chute and pool bedforms all of which are associated with turbulent transcritical to supercritical water flow conditions antidune wavelengths range from 24 to 96 m corresponding to flow velocities of 6 to 12 m sec 1 and average flow depths of 5 to 19 m this range of calculated flow velocities is in good agreement with estimates made from eyewitness accounts architectural analysis of the 1918 jokulhlaup deposits has led to an improved estimation of flow parameters and flow hydraulics associated with the 1918 jokulhlaup that could not have been achieved through localized outcrop analysis the observations presented here provide additional sedimentological and architectural criteria for the recognition of deposits associated with transcritical and supercritical water flow conditions the physical scale of sedimentary architectures associated with the migration of bedforms is largely dependent on the magnitude of the formative flow events or processes sedimentary analyses must therefore be undertaken at the appropriate physical scale if reliable interpretations regarding modes of deposition and formative flow hydraulics are to be made

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

late cretaceous exhumation of the metamorphic gleinalm dome eastern alps kinematics cooling history and sedimentary response in a sinistral wrench corridor abstract the metamorphic gleinalm dome eastern alps was uplifted and exhumed within a releasing structure in a sinistral wrench corridor during the late cretaceous the dome is confined by a system of ductile shear zones including low angle normal faults and steep sinistral tear faults which define a large releasing structure with the metamorphic dome in its center the fabrics developed within all ductile shear zones record processes which were operating during decreasing temperatures from initial epidote amphibolite upper greenschist facies conditions with crystal plastic fabrics in quartz to temperatures below ca 300 c with predominantly cataclastic fabrics a cooling path based on 40ar 39ar amphibole 95 4 1 2 ma and muscovite ages 87 6 0 6 84 3 0 7 ma together with sphene zircon and apatite fission track data indicate cooling through ca 500 c at ca 94 ma to below ca 250 200 c at 65 ma subsidence of the adjacent late cretaceous kainach gosau basin occurred synchronously with cooling and uplift of the gleinalm dome internal depositional patterns record rapid subsidence at the time of cooling with internal synsedimentary block rotation above an intra crustal ductile normal fault the sinistral wrench corridor of the eastern alps developed by sinistral displacement of the austroalpine units against a relatively stable europe during the late cretaceous

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

experimentally produced glass compared with that occurring at the torr nw scotland uk vitrification through biotite melting abstract it is proposed that the vitrification in some iron age forts in nw scotland can be explained through decomposition of micas largely biotite giving melts that react with or dissolve quartz and crystallise orthopyroxene and feldspars so equating with the reaction biotite quartz sanidine orthopyroxene liquid a sample of moine semi pelite has been experimentally melted at c 850 c demonstrating this breakdown reaction a preserved thermal gradient across the sample reveals the progressive degradation of biotite towards the melting upper surface degradation is evident from the initial emphasis of mica cleavages in grains at the bottom of the sample and then appearance and progressive increase in size of bubbles associated with biotite and melt towards the top of the sample a chocolate brown melt was produced as a coating on the upper surface and along micaceous layers a near equivalent sample was located from the fort at the torr that whilst being more thoroughly affected by heat with no unaffected biotite preserved similar textures compositions of original moine minerals are used to constrain the melts produced and melt evolution is tracked through quenched crystals these include ternary feldspars as well as sanidine spinels and orthopyroxene spot geochemical evidence demonstrates the heterogeneity of the melts plus varying contributions of ca and na that could be attributed to the onset of reactions involving feldspars and other minerals from the original assemblage it is thus concluded that a similar temperature to that of c 850 c derived in the experiment was reached in the vitrification process at the torr in order to produce the glass observed

tertiary evolution of the intra carpathian area a model abstract the outer carpathian flysch nappes encircle an intra carpathian domain which can be divided into two megatectonic units north pannonian and tisza mostly on the basis of contrasting mesozoic and palaeogene facies development we see two major kinematic problems to be solved 1 1 the present distribution of the mesozoic and palaeogene facies is mosaic like and some belts form exotic bodies within realms of austroalpine affinity 2 2 late eocene palinspastic reconstruction of the outer carpathian flysch nappes suggest that the entire intra carpathian area must have been located several hundreds of kilometres to the south and to the west of its present position neogene extension can account for shortening in the external carpathian nappes but is unable to explain mesozoic facies anomalies and offsets of palaeogene formations we suggest that evolution of the intra carpathian area involved first late palaeogene early miocene juxtaposition of the north pannonian and tisza megatectonic units accompanied by the closure of the external carpathian flysch troughs thereafter extension of this amalgamated unit occurred which was compensated by thrusting of flysch nappes onto the european foreland and formation of molasse foredeeps eastward escape of the north pannonian unit from the alpine collisional belt involved left lateral shear along the pieniny klippen belt and right lateral shear along the mid hungarian zone parts of the late palaeogene basin and an early miocene volcanic edifice were dissected offset and elongated by several 100 kms the driving mechanism of the eastward escape of the intra carpathian area can be related to the collision of apulia and europe and the subduction of the external carpathian crust under the pannonian units the escape ceased gradually in the early miocene when oblique collision between the north pannonian unit and european continent occurred neogene extension of the pannonian region was an areal deformation the extension at locally variable rate resulted in the break up of the heterogenous floor of the neogene basin the driving mechanism of basin extension and contemporaneous compressional deformation of the external carpathians is thought to be related to ongoing subduction involving the marginal part of the attenuated european continental crust tectonic activity in the carpathians and basin subsidence and volcanism shifted in time and in unison from the west toward the east southeast

internal structural geometry of the paleozoic of graz the paleozoic of graz is an isolated nappe complex of about 1 500 km2 size and belongs to the austroalpine units of the eastern european alps despite more than 500 publications on stratigraphy paleontology and local structure many aspects of the internal geometry of this complex as a whole remained unclear in this contribution we present integrated geological profiles through the entire nappe complex based on these profiles we present 1 a simplified lithological subdivision into 13 rock associations 2 a modified tectonostratigraphy where we consider only two major tectonic units an upper and a lower nappe system and in which we abandon the traditionally used facies nappe concept and 3 a modified paleogeography for the whole complex finally we discuss whether the internal deformation of the paleozoic of graz is of variscan or eo alpine age and which of the published models best explain the tectonic evolution of the paleozoic of graz

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

the evolution of the meliata hallstatt ocean and its significance for the early evolution of the eastern alps and western carpathians abstract the evolution of the meliata hallstatt ocean and of its southern and northern margin in the inner western carpathians are described the main rifting began during the pelsonian and the sea floor spreading ended at the beginning of the middle carnian contemporaneously with the raibl event the subduction began in the latest triassic and the final closing of the ocean accompanied by uplift of the adjacent marginal areas was dated as basal oxfordian remnants of the oceanic suboceanic sequence occur in two tectonic positions 1 obducted nappes that contain mostly as tectonic melanges the whole middle triassic to middle jurassic sequence including large bodies of dismembered ophiolites of ladinian to early carnian age 2 evaporite melanges at the base of nappes that are derived from the northern margin of the ocean these evaporite melanges consist of late permian evaporitic matrix and blocks of a dismembered ladinian to lower carnian ophiolitic sequence in the inner western carpathians both the northern and southern marginal sequences of the meliata hallstatt ocean and the transitions into the carbonate platforms are present in different nappes the southern marginal development is characterized by middle carnian distal clastic raibl beds and by middle jurassic rhyolithic volcanism both missing in the northern marginal development because the subduction related middle jurassic volcanism contemporaneous with the turbidites in the southern meliaticum is restricted to the marginal area south of the meliata hallstatt ocean southward directed subduction is indicated to the south on the adjacent carbonate platform a jurassic basin with aalenian to bajocian ophiolites opened this may be a back arc basin in the eastern alps only the northern marginal zone and the adjacent carbonate platform are preserved but parts of the dismembered ophiolites in the haselgebirge may be of ladinian to late carnian age like in evaporitic melanges in the same tectonic position in the inner western carpathians the final closing of the meliata hallstatt ocean is indicated by the abrupt end of the turbiditic sedimentntation in the oceanic suboceanic domain and by uplift in the marginal areas where lower oxfordian radiolarites are overlain by shallow water upper oxfordian to tithonian or neocomian limestones silica nappe hallstatt nappes with the evidence of the final closing of the meliata hallstatt ocean near the middle late jurassic boundary the cimmerian orogenesis in the genetic sense of engor 1984 1985 is now also proven in the inner western carpathians and in the eastern alps a continuation of the meliata hallstatt ocean into the pontide paleotethys cimmerian ocean sensu kozur 1990 through the transylbanian oceanic domain and the strandzha unit is assumed a connecction with the vardar ocean is impossible because in the vardar zone no triassic ophiolites or basic volcanics are present and the ophiolites have jurassic age

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

deep crustal structure beneath the central and inner west carpathians abstract the 150 km long deep seismic transect 2t crossing the central part of the slovakian west carpathians has revealed an important whole crustal seismic suture zone dipping to the south this zone is dominated by six large and several minor reflection events because of our good knowledge of the surface geology and a large number of comparative studies of the eastern alps it is clear that the upper reflections are due to overthrust sheets that originated during compression of the apulian passive margin tectonically deeper reflections are interpreted as being due to ligurian oceanic igneous and sedimentary rocks sheared in ductile domain during continental collision with the brianconnais passive margin and continental masses north of the central apulian west carpathians cwc behind a significant strike slip fault are the cenozoic structures of the pieniny klippen belt and the magura rhenodanubian flysch south of the cwc the inner tethyan west carpathians iwc are thrust over the cwc the iwc originated during the late jurassic early cretaceous closure of the tethyan ocean and the seismic image of the iwc is different from the highly reflective cwc suture these three pre neogene nappe systems amalgamated as one overthrust system during the neogene subduction of the moldavian sea as the moldavian accretionary wedge the vepor gemer block of the west carpathians where the cretaceous suture is observed has been untouched by any major cenozoic deformation and has remained relatively rigid this unique structure therefore enables us to observe seismically the cretaceous suture zone which elsewhere in the european alpine belt has been almost completely destroyed more general data about the beginning of subduction and subsequent collision processes are presented significant compression and partial subduction of the apulian upper plate passive margin lasted from the hauterivian to the beginning of the turonian for about 25 30 ma subduction of the ligurian ocean occurred from turonian to campanian times after the early campanian the collision of the apulian and brianconnais plates took place

mesozoic plate tectonic reconstruction of the carpathian region abstract palaeomagnetic palaeobiogeographic and structural comparisons of different parts of the alpine carpathian region suggest that four terranes comprise this area the alcapa tisza dacia and adria terranes these terranes are composed of different mesozoic continental and oceanic fragments that were each assembled during a complex late jurassic cretaceous palaeogene history palaeomagnetic and tectonic data suggest that the carpathians are built up by two major oroclinal bends the alcapa bend has the meliata oceanic unit correlated with the dinaric vardar ophiolite in its core it is composed of the western carpathians eastern alps and southern alcapa units transdanubian range bukk this terrane finds its continuation in the high karst margin of the dinarides further elements of the alcapa terrane are thought to be derived from collided microcontinents czorsztyn in the n and a carbonate unit tisza in the se the tisza dacia bend has the vardar oceanic unit in its core it is composed of the bihor and getic microcontinents this terrane finds its continuation in the serbo macedonian massif of the balkans the bihor getic microcontinent originally laid east of the western carpathians and filled the present carpathian embayment in the late palaeozoic early mesozoic the vardar ocean occupied an intermediate position between the western carpathian austroalpine transdanubian high karst margin and the bihor getic serbo macedonian microcontinent the vardar and pindos oceans were opened in the heart of the mediterranean adriatic microcontinent in the late permian middle triassic vardar subducted by the end of jurassic causing the bihor getic serbo macedonian microcontinent to collide with the internal dinaric western carpathian margin an external penninic vahic ocean tract began opening in the early jurassic separating the austroalpine western carpathian microcontinent and its fauna from the european shelf further east the severin ceahlau magura also began opening in the early jurassic but final separation of the bihor getic ribbon and its fauna from the european shelf did not take place until the late middle jurassic the alcapa and the tisza dacia were bending during the albian maastrichtian the two oroclinal bends were finally opposed and pushed into the gates of the carpathian embayment during the palaeogene and neogene at that time the main n s shortening in distant alpine and hellenic sectors was linked by a broader right lateral shear zone along the former vardar suture

evidence for jurassic subduction from the northern calcareous alps berchtesgaden austroalpine germany the closure of the western part of the neotethys ocean started in late early jurassic the middle to early late jurassic contraction is documented in the berchtesgaden alps by the migration of trench like basins formed in front of a propagating thrust belt due to ophiolite obduction these basins propagated from the outer shelf area hallstatt realm to the interior continent hauptdolomit dachstein platform realm the basins were separated by nappe fronts forming structural highs this scenario mirrors syn orogenic erosion and deposition in an evolving thrust belt active basin formation and nappe thrusting ended around the oxfordian kimmeridgian boundary followed by the onset of carbonate platforms on structural highs starved basins remained between the platforms rapid deepening around the early late tithonian boundary was induced by extension due to mountain uplift and resulted in the reconfiguration of the platforms and basins erosion of the uplifted nappe stack including obducted ophiolites resulted in increased sediment supply into the basins and final drowning and demise of the platforms in the berriasian the remaining early cretaceous foreland basins were filled up by sediments including siliciclastics the described jurassic to early cretaceous history of the northern calcareous alps accords with the history of the western carpathians the dinarides and the albanides where 1 age dating of the metamorphic soles prove late early to middle jurassic inneroceanic thrusting followed by late middle to early late jurassic ophiolite obduction 2 kimmeridgian to tithonian shallow water platforms formed on top of the obducted ophiolites and 3 latest jurassic to early cretaceous sediments show postorogenic character

quantifying sample bias in clast fabric measurements chandler d m hubbard b 2008 quantifying sample bias in clast fabric measurements sedimentology 55 4 925 938

cretaceous evolution of a metamorphic core complex the veporic unit western carpathians slovakia p t conditions and in situ40ar 39ar uv laser probe dating of metapelites alpine metamorphism related to the development of a metamorphic core complex during cretaceous orogenic events has been recognized in the veporic unit western carpathians slovakia three metamorphic zones have been distinguished in the metapelites 1 chloritoid chlorite garnet 2 garnet staurolite chlorite 3 staurolite biotite kyanite the isograds separating the metamorphic zones have been modelled by discontinuous reactions in the system k2o feo mgo al2o3 sio2 h2o kfmash the isograds are roughly parallel to the north east dipping foliation related to extensional updoming along low angle normal faults thermobarometric data document increasing p t conditions from c 500 c and 7 8 kbar to c 620 c and 9 10 kbar reflecting a coherent metamorphic field gradient from greenschist to middle amphibolite facies 40ar 39ar data obtained by high spatial resolution in situ ultraviolet uv laser ablation of white micas from the rock slabs constrain the timing of cooling and exhumation in the late cretaceous mean dates are between 77 and 72 ma however individual white mica grains record a range of apparent 40ar 39ar ages indicating that cooling below the blocking temperature for argon diffusion was not instantaneous the reconstructed metamorphic p t t path is clockwise reflecting post burial decompression and cooling during a single alpine orogenic cycle the presented data suggest that the veporic unit evolved as a metamorphic core complex during the cretaceous growth of the western carpathian orogenic wedge metamorphism was related to collisional crustal shortening and stacking following closure of the meliata ocean exhumation was accomplished by synorogenic orogen parallel extension and unroofing in an overall compressive regime

exhumation of high and ultrahigh pressure metamorphic rocks by slab extraction exhumation of high and ultrahigh pressure metamorphic rocks in collisional orogens may be explained by upward extrusion of these rocks erosion of their overburden or extensional thinning of the overburden some high pressure terranes such as the adula nappe in the central alps fit none of these scenarios we propose an additional way in which part of the overburden may be removed it may sink off into the deeper mantle slab extraction structural and metamorphic relationships in and around the adula nappe indicate that the emplacement of this alpine high to ultrahigh pressure nappe to 3 2 gpa in a pile of lower pressure nappes resulted from the interaction of two subduction zones that accommodated the closure of two ocean basins ultimately leading to the extraction of the intervening slab in terms of mechanics the cause of the exhumation is in this case not the buoyancy of the high pressure rocks but the negative buoyancy of the extracted slab

chemical and spectroscopic characteristics of potassium white micas related to polystage evolution of the central western carpathians orogenic wedge abstract potassium white micas in sheared basement and cover rocks from the central western carpathians cwc were investigated by pl microscopy electron microprobe emp analysis mossbauer and micro raman spectroscopy we specified chemical and spectroscopic characteristics which allow distinction between celadonite poor muscovitic and celadonite rich phengitic white mica wmca wmca generations formed during a polystage evolution in changing p t conditions ranging from the very low to medium temperatures at medium pressure within the alpidic cwc orogenic wedge bse imaging emp analyses and x ray element maps indicate chemical differences between muscovite and phengite mainly in al fe and si contents mossbauer spectroscopy revealed their contrasting spectra related to different hyperfine parameters mainly of quadrupole splitting qs of ms 2 6 2 7 mm s or 2 9 3 0 mm s for phg corresponding to fe2 and fe3 contents blastomylonitic samples with a single dominating wmca generation and finite strain xz sections were suitable for micro raman study these data corroborate correlation between the frequencies of two vibrational modes of wmca and si content the investigated wmca generations indicate an enhanced transformation between wmca phases in shear zones

structure and evolution of a rocksalt mudrock tectonite the haselgebirge in the northern calcareous alps the northern calcareous alps are part of the eastern alps in austria and germany the mesozoic units of this fold and thrust belt were detached thrusted and stacked along the evaporitic haselgebirge formation exposed in salt mines rocksalt and mudrock form a two component tectonite the rock type haselgebirge consists of 10 70 wt halite with silt to gravel or block sized components within a halite matrix and the kerngebirge with 70 wt halite all rock types studied are fault rocks by use of a temperature independent subgrain size piezometer the paleo differential stress of halite was calculated at ca 2 5 mpa in altaussee and ca 4 5 mpa in berchtesgaden including data from a grain size piezometer temperatures were estimated at ca 150 20 c and 110 10 c this implies very high strain rates which are about 10 10 10 9 s 1 during the tectonic movement the halite deformed recrystallized and crystallized as veins in mudrock fractures we interpret high overpressure of the pore fluid to have significantly contributed to fracturing of the mudrock

new 40ar 39ar laser single grain ages of muscovites from mylonitic schists in the rodna mountains eastern carpathians romania correlations with microstructure the rodna mountains afford the most internal structural window into the crystalline units of the eastern carpathians in romania the rodna mountains consist of variscan metamorphic nappes that were restacked in the alpine phase of carpathian development forming the subbucovinian and infrabucovinian nappes in order to evaluate age of deformation ten samples were taken from the zone of greenschist facies mylonitic schist that marks the alpine tectonic boundary between the subbucovinian and infrabucovinian nappes and 40ar 39ar laser single grain ages determined for schistosity forming muscovite microstructural assessment of quartz and muscovite distinguished two deformation events single grain ages from the microstructurally most strongly reworked samples four samples give a tight clustering of ages at ca 95 ma the least reworked schists have a broader clustering of ages spanning ca 200 280 ma with a late permian peak and some samples showing outlier ages in the range 200 100 ma the relative development of the outliers which correlates with evidence for increased microstructural reworking is interpreted to mark progressive isotopic resetting the ca 95 ma ages for the most reworked schists are estimates for the age of the alpine nappe stacking the ca 200 280 ma ages are similar to those of magmatism metamorphism and sedimentation thought to mark post variscan pre alpine rifting and ocean basin formation in parts of the alps and may be the thermal imprint of a related event in the eastern carpathians

40ar 39ar ages of crystallization and recrystallization of rock forming polyhalite in alpine rocksalt deposits polyhalite rocks of the evaporitic haselgebirge formation are emplaced within a rocksalt mudrock tectonite the rheologically weak series served as a major detachment level during nappe stacking of the northern calcareous alps eastern alps to test the mineral polyha lite k2ca2mg so4 4 2h2o as a useful geochronometer for various diagenetic and deformation fabric types 40 ar 39 ar age dating was combined with microstructural analysis vein infills poly halite intergrown with anhydrite and polyhalite within mudrock crystallized in several stages between c 235 and 210 ma mylonites of fine grained polyhalite rock indicate subsequent stages of tectonothermal overprint between c 155 and 105 ma which is roughly consistent with previously measured feldspar and muscovite 40 ar 39 ar data from the region illite crystallinity points to temperatures of c 200 8c the peak temperature of overprint was at c 180 8c in the berchtesgaden mine vitrinite reflectance fluid inclusions and 240 8c in the altaussee mine fluid inclusions these temperatures are below the value of 255 8c where polyhalite starts to dehydrate disturbed age spectra patterns result from multiphase polyhalite growth however single phases and comple tely recrystallized fabrics yield good results as in the alpine test case polyhalite may character istically serve as a geochronometer for diagenetic and very low grade metamorphic processes supplementary material a table of used materials and methods and the detailed 40 ar 39 ar step

middle late jurassic sedimentary melange formation related to ophiolite obduction in the alpine carpathian dinaridic mountain range abstract the middle late jurassic mountain building process in the western tethyan realm was triggered by west to northwestward directed ophiolite obduction onto the wider adriatic shelf this southeastern to eastern adriatic shelf was the former passive continental margin of the neo tethys which started to open in the middle triassic its western parts closed from around the early middle jurassic boundary with the onset of east dipping intra oceanic subduction ongoing contraction led to ophiolite obduction onto the former continental margin since the bajocian trench like basins formed concomitantly within the evolving thin skinned orogen in a lower plate situation deep water basins formed in sequence with the northwest westward propagating nappe fronts which served as source areas of the basin fills basin deposition was characterized by coarsening upward cycles i e sedimentary melanges as synorogenic sediments the basin fills became sheared successively by ongoing contractional tectonics with features of typical melanges analyses of ancient neo tethys melanges along the eastern mediterranean mountain ranges allow both a facies reconstruction of the outer western passive margin of the neo tethys and conclusions on the processes and timing of jurassic orogenesis comparison of melanges identical in age and component spectrum in different mountain belts figured out one neo tethys ocean in the western tethyan realm instead of multi ocean and multi continent scenarios

40ar 39ar ages of detrital muscovite and whole rock slate phyllite narragansett basin ri ma usa implications for rejuvenation during very low grade metamorphism late pennsylvanian sedimentary rocks in the narragansett basin were metamorphosed lower anchizone to sillimanite grade during late paleozoic regional metamorphism at ca 275 280 ma twenty five variably sized concentrates of detrital muscovite were prepared from samples collected within contrasting low grade areas diagenesis lower greenschist facies microprobe analyses suggest that the constituent detrital grains are not chemically internally zoned however some grains within several concentrates display very narrow 25 m compositionally distinct low grade epitaxial peripheral overgrowths detrital muscovite concentrates from the lower anchizone are characterized by internally concordant 40ar 39ar age spectra which define plateau ages of ca 350 360 ma these are interpreted to date post devonian acadian cooling within proximal source areas concentrates from lower grade sectors of the middle anchizone display slightly discordant spectra in which apparent ages systematically increase from ca 250 275 ma to define intermediate and high temperature plateaus of ca 360 400 ma detrital muscovite within samples from higher grade sectors of the middle anchizone and the upper anchizone are characterized by systematic low age discordance throughout both low and intermediate temperature increments high temperature ages only range up to ca 330 ma six size fractions of detrital muscovite from a sample collected within the lower greenschist facies have similarly discordant spectra in which apparent ages increase slightly throughout the analyses from ca 250 ma to 275 ma the detrital muscovite results are interpreted to reflect variable affects of late paleozoic regional metamorphism however it is uncertain to what extent the systematic low age spectra discordance reflects intracrystalline gradients in the concentration of 40ar and or experimental evolution of gas from relatively non retentive epitaxial overgrowths however low age discordance occurs regardless of the extent of epitaxial overgrowth intermediate temperature increments evolved during 40ar 39ar whole rock analyses of five slate phyllite samples are characterized by internally consistent apparent k ca ratios these are attributed to gas evolved from constituent very fine grained white mica samples from lower grade portions of the middle anchizone are characterized by intermediate temperature apparent ages which systematically increase from ca 275 300 ma to ca 360 375 ma before evolution of a high temperature contribution from detrital plagioclase feldspar this age variation may reflect partial late paleozoic rejuvenation of very fine grained detrital material with a source age similar to that for the detrital muscovites slate phyllite samples from upper sectors of the middle anchizone and from the upper anchizone were completely rejuvenated during late paleozoic metamorphism and record intermediate and high temperature plateau ages of ca 270 290 ma these data document that metamorphic conditions of the lower to middle biotite zone ca 325 350 c are required to completely rejuvenate intracrystalline argon systems of detrital muscovite therefore the 40ar 39ar dating method may be useful in determination of detrital muscovite provenance and in resolution of the metamorphic evolution of low grade terranes

till fabric patterns and significance particle response to subglacial stress abstract the analysis of particle arrangements within glacial sediments fabric has long been considered to reflect the behaviour of the ice that transported and deposited or deformed the sediment particles can develop specific fabric arrangements as a response to bulk sediment strain driven by effective stress at the bed of a glacier as such fabric analysis has been used to try and understand the complex relationship between glacier and ice sheet dynamics and the geological evidence of former glaciation developments have focused on the use of stereonet patterns and statistical measures vector and eigenvector analysis of clast fabric to infer the process of sediment deposition deformation and consequent ice flow directions and dynamics however as this study identifies fundamental processes of particle orientation march jeffery and taylor rotation mechanisms would suggest more complex explanations than have been previously reported this study reports the results of a detailed field and laboratory investigation of macro scale clast and microfabrics from a till sequence in central scotland the results suggest a systematic behaviour of different particle size fractions which may be interpreted in terms of the strain response of sediment three fabric patterns are identified that illustrate consistent progressively shifting and more complex particle behaviour it is suggested these orientation patterns indicate the degree to which subglacial sediment has undergone strain and the nature of the deforming bed erosional or accretionary it is concluded that this approach may yield fundamental information about the strain conditions underlying different ice masses providing critical data linking glaciological modelling with the sedimentary evidence of glaciation

biotite melting in high grade metamorphic gneisses from the haut allier french massif central in the biotite sillimanite and biotite sillimanite cordierite gneisses from the haut allier french massif central the biotite grains are partially melted they are embayed and replaced by an isotropic material associated with metallic oxides the complete study of this glass by optical microscopy raman spectroscopy electronic microanalysis and x ray diffraction was performed the glassy state is well established locally some very fine kaolinite crystals are present in the glass as hydrothermal reconstruction this glass results from the incongruent melting of biotite the alumino silicate melt corroded the preexistent quartz and feldspar grains anhydrous phases crystallized from this melt successively sillimanite cordierite and quartz correlatively the melt must have become water saturated and a new highly hydrated fluid phase should then have coexisted with it potassium and silicium together with water may have been components of the relatively mobile hydrous phase and this one may have been responsible for some hydration reactions such as muscovitization of feldspars the petrological implications must be emphasized in the studied gneisses biotite cannot be considered as a resister in fact biotite melts and this melting is probably an important agent of the regional anatexis

the metamorphic environment of the sgurr beag slide a major crustal displacement zone in proterozoic moine rocks of scotland new evidence from the sw northern highlands of scotland establishes the southerly extension of the sgurr beag slide interpretation of changes in the mineralogy of calcsilicate rocks particularly the use of the anorthite content of plagioclase feldspar as an index of metamorphic grade together with consideration of the texture and mineralogy of pelitic rocks suggests that the slide juxtaposes crustal segments of different metamorphic grade and history movement on the slide post dates a major phase of regional metamorphism and two phases of regional deformation of precambrian age was synchronous with a regional fold forming event and regional metamorphism at or before c 467 ma caledonian and was followed by regional folding models of the thermal effects of displacement across syn metamorphic shear zones are investigated with particular reference to the roles of thermal relaxation and levels of shear strain a model based on the development of a ductile syn metamorphic asymmetric shear zone best explains the metamorphic patterns associated with the sgurr beag slide an original low to moderate easterly dip is implied with north westerly upthrusting of the eastern crustal block

vitrification of basalt orthostats and mud building components from tilmen hoyuk south eastern turkey an experimental and geoarchaeological approach abstract finds of basalt orthostats and mud building components from the archaeological site of tilmen hoyuk south eastern turkey early 2nd millenium bc preserve a glassy crust formed by vitrification of the material it is proposed that such features are related to destructive fire events which destroyed the wooden building elements and burned natural stones the geoarchaeological and experimental approach confirms this hypothesis the geochemical composition of experimental melts is comparable to that of natural basalts spot analyses evidence the heterogeneity of the melts especially for mudbricks and ceiling plasters it is concluded that the investigated finds were subjected to strong burning under oxidising conditions reached during a violent fire temperatures similar to those derived by experimental melting 1180 1195 c were likely reached in the fire at tilmen in order to produce the glass observed

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

particle fabric and sedimentation of structureless sand southern iceland abstract the interpretation of structureless sand units in terms of flow character and associated depositional mechanism is notoriously difficult to deduce from localized outcrop because such units offer no macroscopic features with which to make distinctions of flow parameters this investigation assesses the significance of directional properties of particle fabric samples taken both vertically and horizontally within structureless sand units deposited by jokulhlaups glacier outburst floods in southwest iceland known to be macroturbulent phenomena based on eyewitness accounts and inferences made from the large scale sedimentary architectures of the deposits given this framework we use particle fabric to verify flow character and depositional mechanism highlighting its potential application to deposits where prior knowledge of conditions is unknown vertical and horizontal trends in particle fabric indicate a causative mechanism that is manifested both spatially and temporally within visually structureless units this data indicates sedimentation onto an aggrading bed beneath a turbulent flow which conforms to the documented turbulent character of the jokulhlaup we demonstrate that cryptic information related to flow parameters can be gleaned from visually structureless sand units through detailed particle fabric analysis and clarify aspects of hyperconcentrated flow behavior and sedimentation

the structure of the hallstatt evaporite body northern calcareous alps austria a compressive diapir superposed by strike slip shear based on old detailed mining maps and own observations in the hallstatt salt mine we reinterpret the structure of the hallstatt evaporite body of the upper permian to lower triassic haselgebirge fm within the northern calcareous alps nca the haselgebirge fm represents a rocksalt mylonite with abundant lenses of sulphates mudstones and limestones in comparison to published results of analogue modeling we interpret the present shape of the hallstatt body as a wnw ese elongated compressive teardrop like diapir this is overprinted by nne ssw shortening and dominantly sinistral shearing along a w trending shear zone the internal structure shows steeply dipping rock units and foliation earlier dextral ductile shear fabrics of likely late early cretaceous age are preserved in sulphate rocks and are subsequently overprinted by mylonitic fabrics in rocksalt and cataclastic fabrics in other rocks the low strength of halite results in recent subvertical shortening and a strain rate e of 8 10 10 s 1 is deduced from deformed subhorizontal boreholes this value is similar to such strain rates 10 10 to 10 9 s 1 estimated by the halite grain size distribution from other salt mines in the nca and thus indicative of sub recent formation of the halite microfabrics

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

morphology sedimentology and palaeohydraulic significance of large gravel dunes altai mountains siberia coarse gravel bedforms which resulted from pleistocene glacial outburst floods are identified as subaqueous dunes comparison of the morphology of these fossil structures with modern dunes shows that the form of two dimensional 2 d transverse dunes and 3 d cuspate and lunate dunes developed in coarse gravels is comparable with sand dune morphology within lesser scale geophysical flows the similarity of the steepest gravel dunes with equilibrium dunes in sand indicates that grain size is not a major factor in constraining primary duneform internal structure indicates that flow over 2 d dunes was relatively uniform but over 3 d bedforms flow was locally variable flow separation and complex streaming of flow occurred over the steepest 3 d dunes cross beds are thin and few approach the angle of repose consequently most dunes did not migrate primarily by avalanching but by stoss entrained gravel transported over the crests rolling down and depositing on the lee slopes the lee formed when flood power was waning some dunes were siightly planed down during falling stage because lee side cross beds tend to be steeper than the angle of the preserved lee slope however silt rich caps indicate that any height reduction was contemporary with the final deposition of foresets post flood modification has been negligible although the modern topography is subdued by loess deposits within the dune troughs lee side sediments are often finer than the stoss slope sediments which indicates

subducted continental margin imaged i n the carpathians of czechoslovakia deep seismic reflection data across the frontal part of the carpathian arc image subducted european continental crust beneath the thick accretionary wedge of the neogene west carpathian arc the upper continental crust of the lower plate is depressed with high curvature to a depth off about 25 km below the arc but the corresponding moho appears to be nearly horizontal flow within the lower crust may account for strain mismatch between the two parts of the subductiog continent although the subdued relief on the moho may partly have evolved after subduction ceased perhaps owing to a gabbro eclogite phase change in a mafic lower crust

evolution of the bukk mountains ne hungary during the middle late triassic asymmetric rifting of the vardar meliata branch of the neotethys ocean based on sedimentological and biostratigraphic investigations of the middle late triassic successions of the bukk mountains the evolution of an upper plate margin of a rifting area was reconstructed the middle anisian shallow water carbonates are succeeded by terrestrial sediments simultaneously with the uplift volcanic activity starts indicating the beginning of the rifting the emersion was followed by rapid subsidence in the late anisian early ladinian which corresponds to the synrift stage based on facies distribution of ladinian carnian sediments the half graben structure of the basement can be outlined coeval existence of platforms and basins is characteristic of this period from the end of the fassanian the subsidence slows down postrift stage at this time the thermal cooling controls the subsidence of the area during the late triassic the edges of the platforms were gradually drowned and basins conquered bigger and bigger areas sediments deposited on the southern shelf of the opening vardar meliata branch of the neotethys ocean show features characteristic to the upper plate part of a rifting area whereas sediments of the northern shelf show features characteristic to the lower plate the opening of the vardar meliata branch of the neotethys ocean follows the asymmetric rifting model of wernicke can j earth sci 22 108 125 1985 and dixon et al tectonics 8 6 1193 1216 1989

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