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

pre clovis in texas a critical assessment of the buttermilk creek complex abstract lithic artifacts from the lowest strata of the debra l friedkin site located on buttermilk creek in central texas have been interpreted as an undisturbed pre clovis assemblage waters et al 2011a stone tools and debitage were recovered from sediments stratified just below diagnostic clovis artifacts and dated by osl to between 13 2 and 15 5 cal kya invoking commonly observed cultural and natural site formation processes we offer an alternative explanation of the buttermilk creek complex as a clovis assemblage in secondary association with the dated sediments

the nappe structure of the central northern calcareous alps and its disintegration during miocene tectonic extrusion a contribution to understanding the orogenic evolution of the eastern alps the classical concept of the nappe structure of the central northern calcareous alps nca is in contradiction with modern stratigraphic structural metamorphic and geochronological data we first perform a palinspastic restoration for the time before miocene lateral tectonic extrusion which shows good continuity of structures facies and diagenetic metamorphic zones we present a new nappe concept in which the tirolic unit practically takes the whole area of the central nca and is divided into three subunits nappes lower and upper tirolic subunit separated by the upper jurassic trattberg thrust and the metamorphic ultra tirolic unit the hallstatt iuvavic nappe s formed the highest unit but were completely destroyed by erosion after nappe stacking remnants of the hallstatt nappes are only represented by components of up to 1 km in size in middle upper jurassic radiolaritic wildflysch sediments hallstatt melange belonging to the tirolic unit destruction of the continental margin started in middle to upper jurassic time and prograded from the oceanic side towards the shelf the original substratum of the external nappes bavaric units of the nca was largely the austroalpine crystalline basement of the internal nappes tirolic units the weakly metamorphosed palaeozoic sequences greywacke zone and equivalents eocene movements caused limited internal deformation in the tirolic unit

authigenic potassium feldspar a tracer for the timing of palaeofluid flow in carbonate rocks northern calcareous alps austria

high accuracy mantle convection simulation through modern numerical methods ii realistic models and problems computations have helped elucidate the dynamics of earth s mantle for several decades already the numerical methods that underlie these simulations have greatly evolved within this time span and today include dynamically changing and adaptively refined meshes sophisticated and efficient solvers and parallelization to large clusters of computers at the same time many of these methods discussed in detail in a previous paper in this series were developed and tested primarily using model problems that lack many of the complexities that are common to the realistic models our community wants to solve today with several years of experience solving complex and realistic models we here revisit some of the algorithm designs of the earlier paper and discuss the incorporation of more complex physics in particular we re consider time stepping and mesh refinement algorithms evaluate approaches to incorporate compressibility and discuss dealing with strongly varying material coefficients latent heat and how to track chemical compositions and heterogeneities taken together and implemented in a high performance massively parallel code the techniques discussed in this paper then allow for high resolution 3d compressible global mantle convection simulations with phase transitions strongly temperature dependent viscosity and realistic material properties based on mineral physics data

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

climate environment and humans in north america s great basin during the younger dryas 12 900 11 600 calendar years ago global climate change associated with the onset of the younger dryas chronozone affected different regions of the northern hemisphere in different ways in the great basin of western north america the effect was positive for human populations relatively cool temperatures causing effectively wetter conditions filled some pluvial basins with shallow but permanent lakes and other basins with wellwatered marshes or meadows vegetation communities dominated by sagebrush and grasses promoted healthy and diverse animal populations ten archaeological sites from the region have been dated to the younger dryas chronozone evidence from these sites indicates that paleoindians with skull shapes and mitochondrial dna similar to modern western north american indians occupied the region these early humans produced a material culture characterized predominantly by large stemmed bifacial points although one site contained a small fluted point curated tool forms and technological activities represented in analyzed lithic assemblages suggest a highly mobile settlement strategy and redundant short term occupations of sites indicate frequent and long distance residential moves across territories spanning distances of up to 400 km paleoindian subsistence pursuits focused on artiodactyls primarily mule deer bighorn sheep and pronghorn antelope leporids chiefly jackrabbits birds sage grouse and waterfowl insects grasshoppers and possibly fish easy to process plants like cactus pads were also eaten but small seeds do not seem to have been an important part of great basin human diets until long after the younger dryas closer to 9500 cal bp the great basin record contains no evidence for natural catastrophe at the onset of the chronozone instead the younger dryas appears to have been among the best of times for human foragers in this region of north america 2011 elsevier ltd and inqua

comment on dna from pre clovis human coprolites in oregon north america gilbert et al reports 9 may 2008 p 786 presented dna analysis of coprolites recovered from an oregon cave as evidence for a human presence in north america before the clovis culture results of our micromorphological and fourier transform infrared spectroscopy analyses of one of the reported coprolites are difficult to reconcile with the dna results identifying the coprolite as human

neoproterozoic tectono thermal evolution of the gariep belt and its basement namibia and south africa abstract within the pan african gariep belt in southwestern africa a para autochthonous predominantly sedimentary sequence deposited in a rift graben and subsequently on a passive continental margin with a kibaran basement is distinguished from an allochthonous predominantly oceanic terrane that was thrust on top of the former during collision of the rio de la plata and the kalahari plates 40ar 39ar mineral cooling ages presented here set the following constraints after kibaran high grade metamorphism the consolidated basement cooled through 300 c at 1006 ma rifting between 781 and 741 ma was followed by the formation of oceanic crust the lower parts of which cooled through 500 c sometime between 630 and 600 ma after inversion from extension to compression some of the oceanic crustal material was shredded off and incorporated into an accretionary wedge a process that is indirectly dated between 573 576 ma by hornblende plateau ages continent continent collision and thrusting of the internal onto the external zones of the tectonic belt culminated between 547 543 ma as indicated by further hornblende plateau ages muscovite cooling ages for the internal zone are between 526 and 529 ma those for the tectonically deeper external zone are 483 ma in the north and between 495 506 ma in the south of the belt in conjunction with published data these results suggest successive closure of first the northern adamastor ocean kaoko belt followed by the khomas sea intracontinental damara belt and finally the southern adamastor ocean gariep belt

authigenic albite in carbonate rocks a tracer for deep burial brine migration euhedral post depositional albite from the eastern and western alps the western carpathians and some greek islands was examined petrographically and geochemically to gain insights into the nature of feldspar reactions in carbonate rocks this study focuses on coarsely crystalline homogeneously nucleated albite in order to avoid problems related to the presence of inseparable detrital material in fine grained albite varieties all albite samples show a very restricted compositional variability and are typically 99 mol ab component unit cell parameters determined by rietveld analysis are slightly more variable than previously accepted but confirm high al si ordering characteristic of low albite the oxygen isotopic composition of albite ranges from 19 4 to 28 3 vsmow there is no direct relationship between the 18o value and the inferred temperature of albite formation nor is there one with stoichiometry the coarse crystal size up to several millimetres in diameter petrographic evidence showing albite cross cutting stylolites greater abundance of albite in carbonate rocks subject to high grade diagenetic or weak metamorphic overprinting and available fluid inclusion data suggest that albite precipitation is favoured at higher temperatures in carbonates than in sandstones pore fluids were invariably brines as suggested by the inferred high positive 18ofluid values the common association of albite bearing carbonates and evaporites and reports of saline fluid inclusions in albite the presence of authigenic albite may thus be a useful tracer of palaeobrine carbonate reactions particularly in deep burial and incipient metamorphic settings

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

the western end of the eoalpine high pressure belt texel unit south tyrol italy eclogites in the texel unit eastern alps south tyrol italy represent the westernmost outcrops of the e w striking eoalpine high pressure belt ehb east of the tauern window the ehb forms part of a cretaceous intracontinental south dipping subduction collision zone however the same nappe stack displays a northwest dip at its western end this prominent change in dip direction gave rise to discussions on the general setting of the eoalpine collision based on our own observations and literature data we present a new tectonic model for the western end of the ehb due to the special situation of this area at the tip of the southalpine indenter originally south east dipping structures became overturned and former thrusts appear as normal faults e g schneeberg fault zone while former normal faults presently display thrust geometries e g jaufen fault thus we explain the current configuration with a coherent eoalpine subduction direction

new evidence for block and thrust sheet rotations in the central northern calcareous alps deduced from two pervasive remagnetization events 1 we present 81 paleomagnetic sites early triassic to early cretaceous from the central sector of the northern calcareous alps nca eastern alps austria and germany stepwise thermal demagnetization defines three magnetic directions mostly carried by low unblocking temperature and low coercivity minerals j3 350 j2 500 j1 575 and 680 j3 and j2 show positive inclinations whereas j1 very seldom is of dual polarity the fold tests show that a j3 can be interpreted as a postfolding and posttilting remagnetization and j2 as a postfolding and pre syn tilting j1 can be considered as primary because of the occurrence of two polarities and evidence presented by other authors in the area all three components show a systematic and significant clockwise rotation after comparing with the expected european references j2 or j1 are marked by higher rotation values than j3 j2 shows different inclinations depending on the structural position north or southward dips considering the structural evolution and the observed inclinations the first postfolding and pretilting remagnetization event j2 could have taken place between late cretaceous and eocene times but certainly before the thrusting of the nca over the rhenodanubian flysch and northward tilting caused by the stacking of the lower austroalpine nappes the second postfolding and posttilting remagnetization j3 would have been acquired after the final thrusting of the nca over penninic units from then the nca behaved as a set of rigid blocks recording the main stage of vertical axis clockwise rotation 65 in average associated with the continental collision the variable degree of rotation in the different positions from 40 to 134 can be explained by individual vertical axis rotation in a block system trying to adjust to space problems the constant declination differences between j2 and j3 25 in average would reflect the rotation related with the lateral differences of shortening during the oblique thrust of the austroalpine units over the penninic units

eo alpine eclogitisation of permian morb type gabbros in the koralpe eastern alps austria new geochronological geochemical and petrological data new petrological geochemical and isotopic data sm nd rb sr from meta gabbros eclogites and metapelites from the southern koralpe are presented pl cpx gabbros mostly olivine free that have preserved their magmatic minerals to varying extent occur as relics within eclogites transformation of gabbro into eclogite is documented in different stages ranging from macro to microscale based on textural characteristics the eclogites are classified into four groups types 1 4 typical eclogite parageneses are grt omp zo ky qtz amp phe rut the metapelitic eclogite host rocks are composed of qtz ms bt pl grt ky p t estimates for both metabasites and metapelites range at 1 8 2 0 gpa 600 650 c sm nd mineral isochrons pl cpx for the gabbroic eclogite precursors give ages of between 247 16 and 255 9 ma their initial nd and sr isotopic compositions are clearly within the range of modern depleted mantle values minerals from type 1 metagabbroic eclogites are in clear nd isotopic disequilibrium pervasively recrystallized type 3 eclogites yield grt wr or grt omp zo amp wr ages of 97 5 101 7 and 109 8 ma the metapelitic eclogite host rocks mica schists yield nd dm depleted mantle model ages of 1 44 1 63 ga grt wr isochron ages from these rocks are 86 1 87 4 and 89 3 ma the new data further support the permian early mesozoic rifting event for this part of the austroalpine basement which is related to initial oceanization at the western end of the alpine tethys during alpine plate convergence pre alpine continental basement and oceanic crustal fragments where subducted to depths of c 60 km the most likely time span for the high pressure peak is c 100 10 ma rapid exhumation in the upper cretaceous is inferred from mineral cooling ages between 80 and 60 ma

initiation of subduction in the alps continent or ocean the triggering event for the modern evolution of the european alps was the onset of subduction in the middle jurassic however there is some debate as to how this onset occurred as 1 oceanic subduction 2 the succession of an earlier tethys and a later penninic oceanic subduction or even 3 intracontinental subduction here we show that it is plausible that the continental lithosphere in the center of the adriatic plate was gravitationally unstable causing the onset of subduction inside the continent this gravitational instability was provided by thermal thickening of the mantle lithosphere in the wake of the permian extensional event and onset of subduction was facilitated by a strong rheological contrast inside the adriatic plate

dynamic models of continental rifting with melt generation abstract active or passive continental rifting is associated with thinning of the lithosphere ascent of the asthenosphere and decompressional melting this melt may percolate within the partially molten source region accumulate and be extracted two dimensional numerical models of extension of the continental lithosphere asthenosphere system are carried out using an eulerian visco plastic formulation the equations of conservation of mass momentum and energy are solved for a multi component crust mantle and two phase solid melt system temperature pressure and stress dependent rheologies based on laboratory data for granite pyroxenite and olivine are used for the upper and lower crust and mantle respectively rifting is modelled by externally prescribing a constant rate of widening with velocities between 2 5 and 40 mm yr a typical extension experiment is characterized by 3 phases 1 distributed extension with superimposed pinch and swell instability 2 lithospheric necking 3 continental break up followed by oceanization the timing of the transition from stages 1 to 2 depends on the presence and magnitude of a localized perturbation and occurs typically after 100 150 km of total extension for the lithospheric system studied here this necking phase is associated with a pronounced negative topography rift valley and a few 100 m of rift flanks the dynamic part of this topography amounts to about 1 km positive topography this means if rifting stops e g due to a drop of external forces immediate additional subsidence by this amount is predicted solidification of ascended melt beneath rift flanks leads to basaltic enrichment and underplating beneath the flanks often observed at volcanic margins after continental break up a second time dependent upwelling event off the rift axis beneath the continental margins is found producing further volcanics melting has almost no or only a small accelerating effect on the local extension value value for a constant external extension rate melting has an extremely strong effect on the upwelling velocity within asthenospheric wedge beneath the new rift this upwelling velocity is only weakly dependent on the rifting velocity the melt induced sublithospheric convection cell is characterized by downwelling flow beneath rift flanks melting increases the topography of the flanks by 100 200 m due to depletion buoyancy another effect of melting is a significant amplification of the central subsidence due to an increase in localized extension subsidence modelled magma amounts are smaller than observed for east african rift system increasing the mantle temperature as would be the case for a large scale plume head better fits the observed magma volumes if extension stops before a new ocean is formed melt remains present and convection remains active for 50 100 myr and further subsidence is significant

magma migration and magmatic solitary waves in 3 d numerical studies of fluid flow in the mantle sug gest that magma migration is an inherently time dependent process that produces magmatic solitary waves from obstruc tions in melt flux previous work has considered one and two dimensional problems here we present the results of three dimensional calculations that utilize a new efficient multi grid scheme we demonstrate that one and two dimensional solitary waves are unstable and break up into sets of 3 d solitary waves which are perfectly spherical when propagat ing through a uniform porosity medium while these waves are not solirons their non linear interactions are qualitatively similar the solitary waves are highly opportunistic and es tablish efficient pathways for migration by linking up with nearby waves when the initial condition is a random dis tribution of porosity the porosity structure can organize into elongate time dependent channels formed from chains of solitary waves these results are natural consequences of the assumptions that the matrix is permeable and viscously deformable we suggest that solitary waves are likely to exist in the mantle and may contribute to the episodicity of mantle magmatism

the generation and composition of partial melts in the earth s mantle abstract a set of equations is presented which combines the constraints of fluid dynamics and multicomponent phase equilibrium to provide a unified description of partial melting in the earth s mantle the equations are applied to a one dimensional model for pressure release melting of a simplified mantle material which contains only two chemical components exhibiting either a complete solid solution or b a binary eutectic in both cases melting occurs over a range of depths the unmelted crystalline residue matrix is modeled as a saturated porous medium through which the melt can migrate because of its differential buoyancy since melt interacts continuously with the matrix during ascent melting occurs by equilibrium rather than fractional fusion this equilibrium fusion is not the same as batch fusion however since material elements are quickly dispersed by migration of melt relative to the matrix to a first approximation the temperature profiles adiabats in the partially molten zone are independent of melt migration the slope of the adiabats varies in inverse proportion to the number of degrees of freedom which characterizes the melting melting of a complete solid solution occurs along a wet adiabat whose slope is controlled by absorption of latent heat melting of a eutectic system occurs along a steeper univariant adiabat until one solid phase is exhausted and subsequently along a wet adiabat the velocity of melt migration can exceed the mantle upwelling velocity by an order of magnitude or more the volume fraction of melt present is always less than the fraction of the material which has melted and is unlikely to exceed a few percent for a wide range of initial conditions melting of a eutectic system produces erupted melts having constant major element composition and widely varying trace element composition this result may provide a partial explanation for the characteristic major and lil element patterns observed in morb liquid compositional paths during pressure release melting cannot be determined from isobaric sections of phase diagrams and can only be calculated by solving the energy equation subject to the appropriate depth dependent phase equilibrium constraints

using palaeoenvironmental dna to reconstruct past environments progress and prospects palaeoenvironmental dna palendna is defined as ancient dna adna originating from disseminated genetic material within palaeoenvironmental samples sources of palendna include marine and lake sediments peat loess till ice permafrost palaeosols coprolites preserved gut contents dental calculus tephras and soils as well as deposits in caves rockshelters and at archaeological sites palendna analysis provides a relatively new tool for quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions testing hypotheses regarding megafaunal extinctions human environment interactions taxonomic studies and studies of dna damage because palendna samples comprise markedly different materials and represent wide ranging depositional and taphonomic contexts various issues must be addressed to achieve robust reproducible findings such issues include climatic and temporal limitations the biological origin and state free versus bound of palendna stratigraphic reliability sterile sampling ability to distinguish modern from adna signals dna damage and pcr amplification dna extraction methods and taxonomic resolution in this review we provide a non specialist introduction to the use of palendna for quaternary and archaeological researchers assess attributes and limitations of this palaeoenvir onmental tool and discuss future prospects of using palendna to reconstruct past environments copyright 2014 the authors journal of quaternary science published by john wiley sons ltd on behalf of quaternary research association

biomolecular and micromorphological analysis of suspected faecal deposits at neolithic catalhoyuk turkey suspected coprolites from midden burial and room fill contexts at catalhoyuk were analysed by gc ms and thin section micromorphology assessment of sterol biomarkers enabled a distinction between faecal and non faecal sources for the deposits to be made with bile acid biomarkers indicating that many of the faecal deposits are human coprolites the relative lack of ruminant faeces could be due to this material being used as a fuel source deposits in burials were observed to contain soil and plant derived sterols rather than their faecal counterparts further analysis in thin section enabled identification of associated materials and contents diagnostic inclusions such as bone and plant fragments were only present in some of the human coprolites which were observed to have a very similar morphology to decayed plant remains this study illustrates the difficulties in distinguishing coprolites in the field and under the microscope and demonstrates the importance of integrating biogeochemical methods particularly when such deposits are used as the basis for interpreting human health and diet and use of space in settlements

wrenching in the external zone of the betic cordilleras southern spain abstract regional structural trends in the caravaca huescar area forming the central part of the external zone in the betic cordilleras indicate that deformation of the area results from right lateral wrenching subparallel to the paleogeographic zonation the structural trends do not fit the nappe interpretation generally used elsewhere in the external zone arguments for wrenching in the area are the structural inverse symmetry with respect to a central transcurrent fault zone the crevillente fault zone the distributional pattern of stratigraphic anomalies and types of deformation and the outcrop pattern of the paleogeographic zones it is argued that certain tectonic units in the area formerly interpreted as klippes in a nappe configuration form centers of flower structures and are vertically squeezed out blocks a theoretical model is sketched illustrating the evolution of a wrench zone under the stratigraphic conditions of the studied area and resulting in its present characteristics many of the features of the caravaca huescar area are also present elsewhere in the external zone and support the idea that wrenching was a major deformational mechanism it is therefore suggested that the external zone should in general not be described in terms of a nappe structure as has been done so far but in terms of a strike slip orogen or a wrenched continental margin

simultaneous melting and compaction in deformable two phase media summary melt generation and extraction are typically modelled using the two phase equations developed by mckenzie or scott and stevenson various approximations are often made to simplify the problem which may lead to some unphysical results e g thermodynamically inconsistent conditions of melting and unrealistic porosity profiles we discuss a generalized version of the set of equations introduced by bercovici et al that allows for mass transfer between the two phases in a single component system and consider a self consistent set of equations in our description the two phases solid and melt are submitted to individual pressure fields whose difference is related to the surface tension at the interfaces changes in porosity and the melting rate a kinetic relation for the melting rate arises from the second law of thermodynamics the condition of chemical equilibrium corresponds to the usual univariant equality of the chemical potentials of each phase when the matrix and melt are motionless in the most general form phase equilibrium is influenced by both the gibbs thomson effect that arises naturally from thermodynamic considerations on surface tension and by the viscous deformation of the phases we apply these new equations to a steady state problem of pressure release melting in a univariant system we treat melting and compaction simultaneously and observe several new effects including multiple domains near the onset of melting that correspond to various force balances a consequence of matrix compaction and melt expulsion or matrix dilation and melt accumulation is a pressure difference between melt and solid that facilitates inhibits melting for parameters corresponding to mid oceanic ridge magmatism compaction permits melting to start as much as 2k m below the standard solidus numerical solutions are necessary to determine the magnitude of the melt zone shift numerical results support the boundary layer solutions obtained analytically and suggest that in most of the melting zone the movement of melt and matrix should be close to the darcy equilibrium where the buoyancy of melt is balanced by the viscous drag between the phases the darcy equilibrium follows an initial stage where the matrix viscous stresses balance darcy drag in all situations the steady state porosity profile remains a monotonic function of depth the existence of a compaction layer following a melting zone where the porosity is maximum as described in various earlier publications has never been found

compositional effect on the pressure derivatives of bulk modulus of silicate melts abstract although the bulk moduli k t 0 of silicate melts have a relatively narrow range of values the pressure derivatives of the isothermal bulk modulus k t 0 can assume a broad range of values and have an important influence on the compositional dependence of the melt compressibility at high pressure based on the melt density data from sink float experiments at high pressures in the literature we calculate k t 0 using an isothermal equation of state eos e g birch murnaghan eos and vinet eos with the previously determined values of room pressure density 0 and room pressure bulk modulus k t 0 the results show that best estimates of k t 0 vary considerably from 3 to 7 for different compositions k t 0 is nearly independent of mg molar mg mg fe but decreases with sio 2 content hydrous melts have anomalously small k t 0 leading to a high degree of compression at high pressures for anhydrous melts k t 0 is 7 for peridotitic melts 6 for picritic melts 5 for komatiitic melts and 4 for basaltic melts

melt segregation and depletion during ascent of buoyant diapirs in subduction zones author posting american geophysical union 2020 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research solid earth 125 2 2020 e2019jb018203 doi 10 1029 2019jb018203

crustal accretion and dynamic feedback on mantle melting of a ridge centred plume the iceland case abstract a major consequence of the interaction of a plume with an oceanic ridge is the enhanced melt production and associated crust generation in the case of iceland crustal thickness as large as 20 to 40 km has been reported crustal seismic velocities are high and have to be explained by thermal or chemical effects in the first part of the paper we address the question whether extraction of melt out of the plume beneath a slowly spreading ridge and deposition of extracted basalt volumes at the surface produces a dynamic feedback mechanism on mantle melting to study this question we solve the convection equations for a ridge centred plume with non newtonian rheology including melting melt extraction associated with deposition of cold crust at the surface of the model and using a simplified approach for compaction the assumption of cold crust is justified if the thickness of each deposited basaltic layer is less than roughly 1 km depending on the buoyancy flux of the plume crustal thicknesses between 10 and 40 km are modelled showing characteristic dipping structures resembling the rift ward dipping basaltic layers of east and western iceland comparing the resulting crustal thickness and magma generation rate with models in which the dynamic effect of crust deposition has been suppressed indicates that melt generation beneath a slowly spreading ridge is considerably damped by the dynamic feedback mechanism if the plume buoyancy flux exceeds 400 to 600 kg s based on the observed crustal thickness of iceland our models predict a plume buoyancy flux of 1140 kg s in the second part we study the accretion of the icelandic crust by a thermo mechanical model in more detail based on the navier stokes the heat transport and the mass conservation equations including volumetric sources hot 1200 c molten crustal material is injected into the newly forming crust with a constant rate at different crustal source regions a deep widespread emplacement of dykes and sills including crustal underplating b magma chambers at shallow to mid crustal level and c surface extrusions and intrusions in fissure swarms at shallow depth connected to volcanic centres we identify the material from the different source regions by a marker approach varying the relative dominance of these source regions characteristic crustal structures evolve showing shallow dipping upper crustal layers with dip angles between 10 and 15 the thermal structure of the crust varies between cold crust shallow source region dominating and hot crust deep source region dominating we use observations of maximum depth of seismicity to constrain the depth of the 650 c isotherm and seismological inferences on the lower crust to constrain temperatures in that region the best agreement with our models is achieved for crust formation dominated by deep dykes and underplating with a considerable influence of magma chamber accretion

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

evolution of the margin of the gulf of california near loreto baja california peninsula mexico the gulf of california is a prime example of a young oblique divergent plate boundary this type of plate boundary is much less well understood than classic rifts and passive margins in divergent plate settings a complexity in the gulf of california is that the modern oblique rifting was preceded by a stage of orthogonal rifting we have used extensive mapping as well as stratigraphic geomorphic and structural analysis to determine the history of deformation near loreto on the southern baja california peninsula during formation of the gulf of california our data support the suggestion that middle to late miocene protogulf stage 12 to ca 6 ma orthogonal rifting was overprinted by transtensional structures during pliocene to quaternary time though we cannot closely define the time of change we further demonstrate that the plate margin was structurally segmented in the protogulf stage and then complexly overprinted by transtensional structures that suggest one type of process for initiating transform faults the loreto segment is 85 km long along the rift and is bounded on the west by a discontinuous series of aligned down tothe east extensional monoclines and normal faults these structures lie along or as far as 4 km in front east of a steep 1000 1600 m high main gulf escarpment that defines the western topographic margin of the rift zone the loreto segment is further defined by a rise in elevation of the main gulf escarpment of up to 1 km and an 500 800 m increase in structural relief of prerift strata in the escarpment from the segment boundaries to the center of the segment structural analysis of secondary faults of the loreto segment shows that fault populations that are known to be pliocene to quaternary in age are mixed normal and dextral normal faults with a bulk extension direction of west northwest eastsoutheast 2808 1008 in contrast fault populations that cut only prerift oligocene middle miocene volcanic and sedimentary rocks are mainly normal faults with northeast southwest to east northeast west southwest bulk extension directions that average 2458 658 these faults are interpreted to be late miocene in age and formed during protogulf orthogonal rifting thus the pliocene faults record a major change of extension direction of 358 from latest miocene to pliocene time compatible with the onset of oblique rifting in the gulf of california oblique divergent overprinting is mainly expressed as the loreto fault and loreto basin in the northern part of the segment the loreto fault and basin evolved with major fault reorganizations and partial basin inversion many observations suggest that the pliocene loreto fault was linked to two nascent transform faults in the gulf and that carmen island rotated 358 408 clockwise within the complex fault system

crustal thermal regime prior to during and after rifting a geochronological and modeling study of the mesozoic south alpine rifted margin an approximately 15 km thick segment of the mesozoic passive continental margin of adria was involved in alpine shortening and is now exposed in the lake como lake lugano area southern alps northern italy and southern swit zerland the segment comprises the monte generoso basin a deep 9 km extensional basin controlled by the activity of the lugano val grande normal fault the paleosurface and mesozoic geometric relations are well preserved so that the kinematics of fault blocks prior to during and after extension are well constrained rb sr 4oar 39ar and zircon fission track data from basement rocks underlying at various the generoso basin depths provide independent estimates on the thermal evolution of the crustal segment during and after rifting most rb sr and 4oar 39ar ages are contemporaneous with the initial stages of rifting late triassic to early jurassic documenting 1 strongly altered thermal conditions before the onset of ex tension and 2 cooling throughout rifting thermal gradients decreased from 60oc km at the onset of extension to 20oc km 4 shortly after breakup zircon fission track ages are juras sic to early cretaceous providing evidence for continued cooling until the beginning of alpine shortening thermoki nematic numerical modeling of the considered crustal segment provides a full two dimensional description of synrift and postrift evolution synthetic time versus temperature curves are extracted from the model and compared with those derived from absolute ages

disequilibrium melting of a two phase multicomponent mantle melt generation and segregation in earth s mantle is typically modelled using the mixture theory of two phase flows which combine a set of conservation laws for mass momentum and energy with phenomenological laws for fluxes of mass and heat most current two phase flow models assume local thermodynamic equilibrium between melt and matrix but geochemical observations suggest disequilibrium transport may play an important role here we generalise the existing two phase flow theories to encompass multiple thermodynamic components and disequilibrium our main focus is on the phenomenological laws describing phase change and we present general disequilibrium melting laws which reduce to the familiar fractional and equilibrium melting laws in appropriate limits to demonstrate the behaviour of our melting laws we address two simple model problems for a binary system melting at constant pressure and melting in a 1 d upwelling column at steady state the framework presented here will prove useful in future for modelling reaction infiltration instabilities in a thermodynamically consistent manner this framework will be useful not only for magma dynamics but for a wide range of reactive two phase flow problems

effect of solid flow above a subducting slab on water distribution and melting at convergent plate boundaries 1 hydrous fluids derived by dehydration of the downgoing slab at convergent plate boundaries are thought to provoke wet melting in the wedge above the downgoing plate we have investigated the distribution of hydrous fluid and subsequent melt in the wedge using two dimensional models that include solid mantle flow and associated temperature distributions along with buoyant fluid migration and melting solid mantle flow deflects hydrous fluid from their buoyant vertical migration through the wedge melting therefore does not occur directly above the region where hydrous fluids are released from the slab a melting front develops where hydrous fluids first encounter mantle material hot enough to melt wet melting is influenced by solid flow through the advection of fertile mantle material into the wet melting region and the removal of depleted material the region of maximum melting occurs where the maximum flux of water from slab mineral dehydration reaches the wet melting region the extent of melting f and melt production rates increase with increasing convergence rate and grain size due to increased temperatures along the melting front and to increased fractions of water reaching the melting front respectively the position of isotherms above the wet solidus varies with increasing slab dip and thereby also influences f and melt production rates applying the understanding of wet melting from this study to geochemical studies of the aleutians may help elucidate the processes influencing fluid migration and melt production in that region estimates of the timescale of fluid migration seismic velocity variation and attenuation are also investigated

archaeological soil and pollen analysis of experimental floor deposits with special reference to butser ancient farm hampshire uk archaeological stratigraphies that may contain floors are often encountered for more than a decade soil micromorphologists working on archaeological sequences have benefited from having access to reference thin sections of ethnoarchaeological and experimental floors including those from the floors of iron age houses reconstructed by the late dr peter reynolds at butser ancient farm hampshire uk this paper reports upon experimental studies mainly carried out at butser during 1990 95 and their suggested application to microstratigraphic and microfacies analysis of occupation sites sampling at butser in 1990 was very much a rescue operation nevertheless fundamental differences in soil micromorphology were found between domestic house beaten floor deposits and those formed in a stable these differences were also reflected in the parallel study of pollen from these deposits with microchemical analyses helping to explain anomalous pollen preservation in the unsuitable soil at butser the limited bulk chemical study produced less clear results but when compared with findings from some roman and early medieval sites in london showed that the chemical trends hinted at butser are probably replicated in some ancient floors a preliminary interdisciplinary study of samples from the london guildhall clearly suggested the potential of such microstratigraphical and microfacies analyses and intimates at the potential of attaining rigorous consensus interpretations stable floor deposits are both organic and phosphate rich with homogeneous soil micromorphological and pollen characteristics beaten floors are much more mineralogenic and heterogeneous in terms of their microfabric and pollen that also indicate trampling in of a wide variety of allocthonous materials the last commonly responsible for raised magnetic susceptibility at archaeological sites these findings prove the worth of the ethnoarchaeological simulations carried out at the moel y gar stable and domestic pimperne house this microfacies approach is viewed as complementary to site reconstruction through macrofossil analysis of beetles and plant remains especially where sites are being investigated at the microstratigraphic level the phosphate content of stabling deposits may allow preservation of pollen in what may otherwise be deemed unsuitable material as demonstrated at butser

repeat ridge jumps associated with plume ridge interaction melt transport and ridge migration 1 repeated shifts or jumps of mid ocean ridge segments toward nearby hot spots can produce large long term changes to the geometry and location of the tectonic plate boundaries ridge jumps associated with hot spot ridge interaction are likely caused by several processes including shear on the base of the plate due to expanding plume material as well as reheating of lithosphere as magma passes through it to feed off axis volcanism to study how these processes influence ridge jumps we use numerical models to simulate 2 d in cross section viscous flow of the mantle viscoplastic deformation of the lithosphere and melt migration upward from the asthenospheric melting zone laterally along the base of the lithosphere and vertically through the lithosphere the locations and rates that magma penetrates and heats the lithosphere are controlled by the time varying accumulation of melt beneath the plate and the depth averaged lithospheric porosity we examine the effect of four key parameters magmatic heating rate of the lithosphere plate spreading rate age of the seafloor overlying the plume and the plume ridge migration rate results indicate that the minimum value of the magmatic heating rate needed to initiate a ridge jump increases with plate age and spreading rate the time required to complete a ridge jump decreases with larger values of magmatic heating rate younger plate age and faster spreading rate for cases with migrating ridges models predict a range of behaviors including repeating ridge jumps much like those exhibited on earth repeating ridge jumps occur at moderate magmatic heating rates and are the result of changes in the hot spot magma flux in response to magma migration along the base of an evolving lithosphere the tendency of slow spreading to promote ridge jumps could help explain the observed clustering of hot spots near the mid atlantic ridge model results also suggest that magmatic heating may significantly thin the lithosphere as has been suggested at hawaii and other hot spots

compaction around a rigid circular inclusion in partially molten rock conservation laws that describe the behavior of partially molten mantle rock have been established for several decades but the associated rheology remains poorly understood constraints on the rheology may be obtained from recently published experiments involving deformation of partially molten rock around a rigid spherical inclusion these experiments give rise to patterns of melt segregation that exhibit the competing effects of pressure shadows and melt rich bands such patterns provide an opportunity to infer rheological parameters through comparison with models based on the conservation laws and constitutive relations that hypothetically govern the system to this end we have developed software tools to simulate finite strain two phase flow around a circular inclusion in a configuration that mirrors the experiments simulations indicate that the evolution of porosity is predominantly controlled by the porosity weakening exponent of the shear viscosity and the poorly known bulk viscosity in two dimensional simulations presented here we find that the balance of pressure shadows and melt rich bands observed in experiments only occurs for bulk to shear viscosity ratio of less than about five however the evolution of porosity in simulations with such low bulk viscosity exceeds physical bounds at unrealistically small strain due to the unchecked exponential growth of the porosity variations processes that limit or balance porosity localization should be incorporated in the formulation of the model to produce results that are consistent with the porosity evolution in experiments

magma ascent by porous flow porous flow of buoyant liquid through partially molten rock is regarded as the initial transport process leading to magma segregation in the mantle recent work has identified the importance of matrix deformation and compaction in this process we present finite difference calculations based on a generalized form of darcy s law that includes matrix deformation in two dimensional cartesian and cylindrical coordinates we emphasize the existence of solitary wave solutions called magmons these waves are regions of locally high porosity that ascend through regions of low uniform porosity they differ from diapirs where the liquid and matrix ascend together the one dimensional waves that were previously reported are found to be unstable in two dimensions breaking down to form two dimensional waves of circular cross section both the development of the instability and the form of the two dimensional waves are supported by theoretical analysis numerical experiments in which two dimensional waves collide show that the extent to which they are conserved after collision depends on the lateral offset of the waves the conservation can be very good in other cases larger waves appear to grow at the expense of smaller waves although the quantification of the relevant permeability and rheological parameters remains uncertain geophysically plausible estimates suggest wavelengths of kilometers and velocities of centimeters per year in our preliminary assessment of the relevance of these results to igneous processes we find that magmons are unlikely to be important in regions of broad upwelling such as beneath spreading centers here the transport of liquid adjusts to match the supply by melting and compaction processes are not important if liquid is supplied from below to a stable partially molten region of the asthenosphere it is expected to ascend in magmons this may occur beneath oceanic volcanic centers or in subcontinental mantle it is possible that magma ascent in magmons leads to spatial and temporal episodicity of volcanic activity if higher level processes do not obscure this influence the waveform of a magmon ascends faster than the liquid within the magmon so new liquid is taken in from above while original liquid is lost from below consequently magmons can mobilize small degrees of partial melt and deliver it rapidly to the surface

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

mesozoic paleogeography of the northern calcareous alps evidence from paleomagnetism and facies analysis the northern calcareous alps are generally thought to have been part of the same southern tethyan continental margin as the southern alps during late jurassic and early cretaceous time contrasting liassic paleomagnetic data from the northern calcareous alps and the southern alps can be explained by large scale clockwise rotation during late cretaceous and tertiary tectonic emplacement of the northern calcareous alps onto the european continental margin alternatively the data can be reconciled by postulating that the northern calcareous alps did not undergo the african mesozoic rotational history seen in the southern alps and were separated from the southern alps by a short lived branch of jurassic ocean facies analysis in the karwendel thiersee syncline of the northern calcareous alps indicates that the jurassic basin sediments in this area were deposited in an east west oriented sinistral strike slip fault system in the southern alps and central austroalpine complex coeval basin sedimentation was controlled by north south oriented normal faults this contrasting basin evolution and evidence for a source of ophiolitic detritus south of the northern calcareous alps argue for a short lived ocean basin south of the northern calcareous alps that was closed by early cretaceous time

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

sediment creep on slopes in pelagic limestones upper jurassic of northern calcareous alps austria abstract slump structures in upper jurassic pelagic limestones of the northern calcareous alps were studied using methods of ductile structural geology the early deformation observed cannot be explained by conventional models for slumping commonly describing slump complexes with an extending upper and contracting lower part instead the structures suggest distributed bedding parallel surficial stretching and folding localized by roll over normal faulting the initially isoclinal and recumbent folds are pervasively overprinted by stretching causing reorientation of fold axes into the downslope direction transport of folds separates antiformal and synformal hinges and the resulting isolated hinges resemble intrafolial folds in metamorphic terranes only folds formed late in the process of lithification allow insight in the early stages of fold evolution we suggest that this type of early deformation represents sediment creep that may be characteristic for slump structures in pelagic carbonates

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

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

chronology and ecology of late pleistocene megafauna in the northern willamette valley oregon abstract since the mid 19th century western oregon s willamette valley has been a source of remains from a wide variety of extinct megafauna few of these have been previously described or dated but new chronologic and isotopic analyses in conjunction with updated evaluations of stratigraphic context provide substantial new information on the species present timing of losses and paleoenvironmental conditions using subfossil material from the northern valley we use ams radiocarbon dating stable isotope 13c and 15n analyses and taxonomic dietary specialization and habitat preferences to reconstruct environments and to develop a local chronology of events that we then compare with continental and regional archaeological and paleoenvironmental data analysis of twelve bone specimens demonstrates the presence of bison mammoth horse sloth and mastodon from 15 000 13 000 cal yr bp the latest ages coincide with changing regional climate corresponding to the onset of the younger dryas it is suggested that cooling conditions led to increased forest cover and along with river aggradation reduced the area of preferred habitat for the larger bodied herbivores which contributed to the demise of local megafauna archaeological evidence for megafauna human interactions in the pacific northwest is scarce limiting our ability to address the human role in causing extinction

a calculated petrogenetic grid for the system k2o feo mgo al2o3 sio2 h2o with particular reference to contact metamorphosed pelites a petrogenetic grid is presented for the system kfmash k o feo mgo a1 0 sio h o including biotite muscovite k feldspar chlorite chloritoid staurolite cordierite garnet ortho amphibole orthopyroxene spinel andalusite sillimanite kyanite quartz and corundum with h o in excess which was calculated using the computer program thermocalc and the powell and holland internally consistent thermodynamic dataset by removing the normal constraint of having quartz in excess both quartz bearing and quartz absent equilibria are shown quartz absent equilibria are particularly relevant at high t and low p conditions because of their common occurrence at these conditions the calculated mineral assemblage and mineral compositional variations in terms of femg and fe mg siall exchange vectors are broadly compatible with observations on natural rocks particularly when non kfmash components are taken into account

a new formulation for coupled magma mantle dynamics many open problems in the earth sciences can only be understood by modelling the porous flow of melt through a viscously deforming solid rock matrix however the system of equations describing this process becomes mathematically degenerate in the limit of vanishing melt fraction numerical methods that do not consider this degeneracy or avoid it solely by regularising specific material properties generally become computationally expensive as soon as the melt fraction approaches zero in some part of the domain here we present a new formulation of the equations for coupled magma mantle dynamics that addresses this problem and allows it to accurately compute large scale 3 d magma mantle dynamics simulations with extensive regions of zero melt fraction we achieve this by rescaling one of the solution variables the compaction pressure which ensures that for vanishing melt fraction the equation causing the degeneracy becomes an identity and the other two equations revert to the stokes system this allows us to split the domain into two parts and to solve the coupled magma mantle dynamics system only in cells where melt is present we have implemented this formulation in the open source geodynamic modelling code aspect and illustrate the improved performance compared to the previous three field formulation showing numerically that the new formulation is optimal in terms of problem size and only minimally sensitive to model parameters beyond that we demonstrate the applicability to realistic problems by showing large scale 2 d and 3 d models of mid ocean ridges with complex rheology hence we believe that our new formulation and its implementation in aspect will prove a valuable tool for studying the interaction of melt segregating through and interacting with a solid host rock in the earth and other planetary bodies using high resolution three dimensional simulations

solitary waves in magma dynamics we investigate the stability of the one dimensional solitary waves solutions of the equations proposed by mckenzie to model the ascent of melts in the earth interior we show that for small porosity and two dimensional horizontal disturbances with long wavelength these solitary waves are unstable we also exhibit two and three dimensional solitary wave solutions of the mckenzie equations

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

significance of late permian triassic facies zones in terrane reconstructions in the alpine north pannonian domain abstract the present day setting of the tectonic units terranes making up the pre neogene basement of the pannonian basin and the west carpathians is the result of large scale displacements during the alpine collisional phases to explain this setting based on various concepts a number of models have been proposed in the last decade most of them agree in an eastward escape of the north pannonian terrane from the alpine domain towards the pannonian during the palaeogene early miocene period in the present paper a reconstruction of the pre escape setting of the displaced terranes is presented based on facies zones in selected time slices from the late permian to the late triassic according to our reconstruction the inner west carpathian units were located east of the austroalpine units forming the northern shelf of the euhallstatt meliatic basin of the vardar oceanic branch the drauzug should have been located in a position much more external than its present day setting the transdanubian range was situated in the northern neighbourhood of the southern alps whereas the bukk may have been located adjacent to the nw dinarides the mid transdanubian zone is a major shear zone containing elements of the julian alps and sava folds nappe system and the inner dinaric ophiolitic melange although the nappe tectonism may have played an important role in the structural evolution of the north pannonian terrane this mechanism alone can hardly produce hundreds of kilometres of facies offset on the opposite sides of strike slip zones

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

olivine flotation in mantle melt abstract molten komatiite and peridotite have been compressed in an octahedral multi anvil device up to 10 gpa densities of the melts were measured at pressure intervals in the range 7 to 10 gpa by observing sinking and floating san carlos olivines and synthetic forsterite marker spheres the multi anvil results for komatiite when combined with piston cylinder measurements done at 4 to 6 gpa and a calculated reference density at 105 pa yield a birch murnaghan isothermal bulk modulus of k1900c 26 gpa and pressure derivativek 4 25 the pressure of neutral buoyancy for olivine in komatiite is confirmed to be near 8 gpa as predicted in earlier work olivine flotation in the experimental komatiite commences at a pressure close to where the liquidus phase changes from olivine to denser garnet leading to the possibility of density driven crystal sorting during fractionation molten peridotite klb 1 shows an isothermal compression 2000 c of 0 065 g cm 3 gpa 1 in the interval 105 pa to 8 2 gpa the olivine liquid peridotite density crossover is predicted to lie between 9 and 11 gpa indicating that olivine flotation can operate at depths of 300 500 km in a molten peridotitic mantle

sandstone diagenesis in a halite deposit from surface to high grade diagenesis haselgebirge formation eastern alps abstract the evaporitic haselgebirge formation of the northern calcareous alps was deposited in an evolving rift during the upper permian the jurassic to cretaceous alpine orogenesis caused an overprint of 200 c the aim of the study was to investigate the diagenetic evolution of these evaporite dominated sediments from intact sandstone lenses field work thin section analysis sem and xrd were completed by measurements of organic material and age dating in this paper we show that all authigenic minerals developed step by step on a prograding path but under low temperatures of

dating fault gouges geological faults are fractures in the earth s crust along which there has been some displacement and are thus zones of weakness which are of importance in planning civil engineering projects constructing underground caverns and conducting earthquake research to assess the potential for future displacements and fluid circulation along faults it is helpful to establish the age of the latest episode of mineral growth in fault zones however there have been few attempts to date recrystallized and newly grown minerals developed in fault zones at low temperature1 4 here we report k ar and rb sr ages for clay fractions from two fault zones in the eastern alps and compare them with ages of the same fine fractions from the undeformed host rock the results suggest that the bulk of the clays along these faults were formed during early cretaceous and tertiary times respectively no major displacements seem to have taken place in recent times

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

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

torsion of a cylinder of partially molten rock with a spherical inclusion theory and simulation the processes that are involved in migration and extraction of melt from the mantle are not yet fully understood gaining a better understanding of material properties of partially molten rock could help shed light on the behavior of melt on larger scales in the mantle in this study we simulate three dimensional torsional deformation of a partially molten rock that contains a rigid spherical inclusion we compare the computed porosity patterns to those found in recent laboratory experiments the laboratory experiments show emergence of melt rich bands throughout the rock sample and pressure shadows around the inclusion the numerical model displays similar melt rich bands only for a small bulk to shear viscosity ratio five or less the results are consistent with earlier two dimensional numerical simulations however we show that it is easier to form melt rich bands in three dimensions compared to two the addition of strain rate dependence of the viscosity causes a distinct change in the shape of pressure shadows around the inclusion this change in shape presents an opportunity for experimentalists to identify the strain rate dependence and therefore the dominant deformation mechanism in torsion experiments with inclusions

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

density of basaltic melt at high pressure and stability of the melt at the base of the lower mantle abstract we made density measurements of model morb and picritic melts up to about 15 gpa using the floating diamond method the compression behavior of the melts is fitted by the vinet equation of state and extrapolated to higher pressure a density crossover between the morb melt and the mantle peridotite is suggested at the base of the lower mantle thus the ultra low velocity zone in the d layer may be explained by the existence of gravitationally stabilized basaltic melt formed by melting of the accumulated slab materials this region might become unstable due to progressive melting of slab materials and or supply of volatiles

equilibria within the mineral assemblage quartz muscovite biotite garnet plagioclase and implications for the mixing properties of octahedrally coordinated cations in muscovite and biotite interaction parameters derived using empirical calibration methods indicate strong non ideality in the mixing of octahedrally coordinated cations in muscovite and biotite the data set used for calibration comprises mineral compositions from 49 samples containing quartz muscovite biotite garnet plagioclase and al2sio5 kyanite or sillimanite pressures and temperatures in the data set were determined through the simultaneous application of geothermometry based on the garnet biotite femg1 exchange equilibrium and geobarometry based on the anorthite breakdown equilibrium two equilibria yielded simple expressions from which binary interaction parameters for octahedrally coordinated cations in biotite could be directly determined a four component fe2 mg al ti regular symmetric mixing model was assumed for biotite one equilibrium yielded a simple expression from which an interaction parameter for the mixing of the mgal celadonite component in muscovite could be directly determined two sets of calculations were performed utilizing different calibrations of the garnet biotite geothermometer and the anothite breakdown geobarometer and different garnet activity models both placed samples within or near the stability field of the al2sio5 phase present in each sample and both yielded similar values for the interaction parameters within narrow uncertainties indicating that the values are insensitive to differences in the underlying methods using the derived interaction parameters activity models were formulated for the annite phlogopite eastonite and siderophyllite components of biotite and for the mgal celadonite component of muscovite these were utilized for the empirical calibration of 45 fluid independent equilibria involving unique combinations of phase components from the mineral assemblage garnet plagioclase biotite muscovite quartz forty three of the equilibria may be applied as geobarometers to equilibrium assemblages of quartz muscovite biotite garnet plagioclase when care is taken to insure that applications are restricted to valid compositional ranges for these the calibrations yielded multiple correlation coefficients ranging from 0 953 to 0 998 and standard deviations of the residuals ranging from 597 to 118 bars

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