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

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

dissolution kinetics and biodurability of tremolite particles in mimicked lung fluids effect of citrate and oxalate abstract the effect of citrate and oxalate on tremolite dissolution rate was measured at 37 c in non stirred flow through reactors using modified gamble s solutions at ph 4 macrophages 7 4 interstitial fluids and 5 5 intermediate check point containing 0 0 15 1 5 and 15 mmol l 1 of citrate or oxalate the dissolution rates calculated from si concentration in the output solutions without organic ligands depend on ph decreasing when the ph increases from 13 00 ph 4 to 13 35 ph 7 4 mol g 1 s 1 and following a proton promoted mechanism the presence of both ligands enhances dissolution rates at every ph increasing this effect when the ligand concentration increases citrate produces a stronger effect as a catalyst than oxalate mainly at more acidic phs and enhances dissolution rates until 20 times for solutions with 15 mmol l 1 citrate however at ph 7 4 the effect is lighter and oxalate solutions 15 mmol l 1 only enhances dissolution rates eight times respect to free organic ligand solutions dissolution is promoted by the attack to protons and organic ligands to the tremolite surface magnesium speciation in oxalate and citrate solutions shows that mg citrate complexes are more effective than oxalate ones during the alteration of tremolite in magrophages but this tendency is the opposite for interstitial fluids being oxalate magnesium complexes stronger the biodurability estimations show that the destruction of the fibers is faster in acidic conditions macrophages than in the neutral solutions interstitial fluid at ph 4 both ligands oxalate and citrate reduce the residence time of the fibers with respect to that calculated in absence of ligands nevertheless at ph 7 4 the presence of ligands does not reduce significantly the lifetime of the fibers

pt paths from modal proportions application to the koralm complex eastern alps thermodynamic pseudosections portray those parts of a petrogenetic grid that are relevant to a given bulk composition and the reactions appearing on them can therefore be used directly to infer the pt path that the rock followed however for many normal bulk compositions the use of pseudosections is hampered by the fact that they display only few large fields of high thermodynamic variance in the pt range of interest here it is discussed how modal information on reaction progress within these fields can be used to determine pt path information for thermodynamically high variant metamorphic assemblages we use this information on reaction progress to contour pseudosections for modal proportions of minerals using the software package thermocalc the approach is applied to di tri and quadrivariant assemblages from the koralm complex in the eastern alps a pt path for these rocks is derived from modal considerations and compared with interpretations of mineral composition contours on the same pseudosection and with conventional thermobarometry it is shown that at least part of the complex must have cooled initially near isobarically from prevalent peak conditions around 700 c and 14 kbar before the rocks commenced a barroviantype decompression path

eastern alpine tectono metamorphic evolution constraints from two dimensional p t t modeling we use two dimensional 2 d p t t modeling to constrain the thermal and rheological aspects of different scenarios for the late mesozoic and cenozoic tectonic evolution of the eastern alps inferred from excellent data sets from the tauern window tw models invoking subduction of the south penninic sp oceanic lithosphere during thrusting and subsequent erosion of the austro alpine aa upper plate nappe stack are inconsistent with the observed thermal evolution within the aa and penninic units in these models predictions for the aa peak thermal conditions are lower than observed after exhumation and cooling to midcrustal levels and subduction of the continental middle penninic mp block the aa undergoes a phase of renewed heating to almost the previous peak temperatures simultaneously the penninic units experience a phase of heating upon subduction followed by cooling after onset of subduction of the north penninic np basin the model predictions are inconsistent with the observed nearly isothermal uplift path of the sp after subduction and cannot explain observed inverted metamorphic peak conditions in the deeper aa amphibolite facies down to the higher penninic unit greenschist facies a model with the beginning of subduction of the sp occurring after crustal thickening of the aa and subsequent return to normal crustal thicknesses is compatible with the p t t data in this model peak temperature conditions are higher in the aa followed by a phase of strong cooling in the aa upper plate with the onset of underthrusting this model also explains successfully nearly isothermal exhumation of the mp and inverted metamorphic peak conditions in the deeper aa material accreted to the hanging wall from the oceanic crust sp experiences a phase of cooling during ongoing subduction of oceanic lithosphere and begins to heat up to its thermal climax after the subduction of trailing continental lithosphere the subsequent pt path of the penninic units strongly depends on the timing and rates of underthrusting by the foreland observed pt paths in the mp within the tw require continuous subduction of the np and the trailing european foreland under the exhuming mp block documented rapid cooling in the final uplift phase of the penninic units in the tw requires exhumation rates up to approximately 4 mm yr predictions of slightly elevated present day geothermal gradients in the tw area are consistent with available heat flow data as a result of mesozoic rifting followed by late mesozoic crustal thickening of the aa paleorheological reconstructions are characterized by a contrast between relatively strong oceanic lithosphere and adjacent weak continental lithosphere predicted decoupling of weak continental and oceanic lithosphere during subsequent subduction of the penninic units can explain observed late cretaceous crustal extension in the aa units in terms of gravitational spreading ongoing subduction leads to an overall strength increase due to underthrusting of cool oceanic lithosphere whereas subduction of continental lithosphere causes a strength decrease in the upper levels of the lithosphere continuous crustal thickening and relaxation of the depressed isotherms reduce the strength of the lower lithospheric mantle beneath the central orogen further enhanced by rapid late stage uplift predictions for the present day rheological structure of the eastern alps support the existence of a strong upper crustal layer two wedge shaped strong upper mantle layers to the north and the south of the orogen and a weak upper mantle underlying the central orogen

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

biodurability of chrysotile and tremolite asbestos in simulated lung and gastric fluids chrysotile mg 3 si 2 o 5 oh 4 and tremolite ca 2 mg 5 si 8 o 22 oh 2 asbestos represent two distinct mineralogical categories of regulated asbestos commonly evaluated in epidemiological toxicological and pathological studies human respiratory and gastric systems are sites of asbestos deposition where chrysotile and tremolite asbestos are undersaturated with respect to biological fluids and dissolution kinetics control the persistence of these minerals in biological environments here we examined the biodurabilities i e the resistance to dissolution of chrysotile and tremolite asbestos in simulated body fluids as a function of mineral surface area over time batch experiments in simulated gastric fluid sgf hcl and nacl solution at ph 1 2 and simulated lung fluid slf modified gamble s solution at ph 7 4 were performed at 37 c over 720 h to evaluate the dissolution of chrysotile vs tremolite asbestos in acidic and near neutral biological fluids the rate limiting step of si release for both minerals was used to obtain rate constants k and reaction orders n allowing comparisons of mineral dissolution rates both chrysotile and tremolite asbestos are less biodurable in sgf low ph compared to slf near neutral ph based on equivalent surface area comparisons the surface chemistry of tremolite is more reactive in lung fluid than chrysotile and vice versa in digestive fluid however the relative biodurabilities of these asbestos silicates from most to least are tremolite slf chrysotile slf tremolite sgf chrysotile sgf when accounting for the greater surface area of chrysotile per mass or per fiber compared to tremolite overall this study illustrates the importance of surface area and fiber morphology considerations when evaluating the biodurabilities of asbestiform minerals

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

thermal history of the sonnblick dome south east tauern window austria implications for heterogeneous uplift within the pennine basement the sonnblick dome is one of several domal structures affecting the interface between basement and cover within the pennine zone of the tauern window in the eastern alps rb sr isotopic data comprising 19 biotite and 22 white mica ages from variably deformed granitic gneisses provide new evidence of the thermal and tectonic history of the dome and its relationships with other parts of the south east tauern window white mica ages generally cluster between 26 and 30 ma although there are values up to 82 ma which appear to reflect incomplete equilibration during tertiary metamorphism under low amphibolite facies conditions six closely spaced samples from an intensely sheared gneiss lamella are more tightly grouped between 26 and 27 6 ma and provide the best estimate of the age of syntectonic crystallization biotite ages are systematically younger ranging from 19 to 23 5 ma reflecting closure during post metamorphic cooling sonnblick dome and the hochalm dome approximately 20 km further east where closure of rb sr in biotite did not occur until 16 5 ma the metamorphic peak here is also probably younger possibly as late as 22 ma the sonnblick dome was formed before 27 ma and the deformation style had changed to extension before biotite closure by 19 ma in contrast rapid updoming in the hochalm dome was previously dated at 16 5 ma and the differences in thermal history can be linked to differences in deformation history overall the geochronological data from the south east tauern window demonstrate the heterogeneity of thermal history on a geographical scale of 10 km and emphasize the importance of tectonic displacements in controlling temperature within orogenic belts

palaeogeography and geodynamic evolution of the gosau group of the northern calcareous alps late cretaceous eastern alps austria abstract the sedimentation of the late cretaceous gosau group of the northern calcareous alps records the complex geodynamic evolution of the northern part of the austroalpine microplate the tectonically controlled sedimentation and facies distribution were mainly governed by the oblique subduction of the pennic ligurian ocean below the austroalpine margin most of the gosau successions comprise two distinct sedimentary complexes the lower gosau subgroup upper turonian campanian is characterized by terrestrial to shallow marine facies associations alluvial fan and fan delta deposits shallow marine sandstones and sandy limestones and storm influenced nearshore and shelf deposits during the early santonian sea level highstand a great part of the northern calcareous alps was covered by a shallow shelf sea palaeotransport directions point to source areas situated both to the north and to the south of the northern calcareous alps the upper gosau subgroup upper santonian eocene comprises deep water hemipelagic and turbiditic deposits rapid subsidence into bathyal to abyssal depths started diachronously from the northwest santonian to the southeast maastrichtian after a short phase of deformation and erosion abyssal deposits in the northern parts of the northern calcareus alps and north directed palaeotransport indicate a tilting of the slope towards the north this subsidence pulse is attributed to an event of subcrustal tectonic erosion probably triggered by the subduction of a topographic high of the south penninic ocean the relationships of the gosau group of the austroalpine unit to late cretaceous deposits of the carpathians and southern alps are discussed in the framework of a plate tectonic model

comparative mineralogy geochemistry and conditions of formation of two metasomatic talc and chlorite deposits trimouns pyrenees france and rabenwald eastern alps austria the trimouns french pyrenees and rabenwald austrian alps talc and chlorite deposits occur within paleozoic metamorphic series hercynian metamorphism and are primarily of sedimentary origin they were produced by metasomatism in zones of intense deformation thrust planes surfaces of tectonic slicing of late hercynian trimouns and alpine rabenwald age the study of the mineral assemblages and the mineral chemical composition chlorites phengites in the various metasomatic zones demonstrates a near attainment of local equilibrium and points to a contrast in crystallization conditions approximately t 400 degrees c and p 1 kbar at trimouns t 500 degrees to 550 degrees c and p 8 to 9 kbars at rabenwald where the talcphengite assemblage is characteristic talc rich ores originate from carbonates dolomite magnesite whereas mg chlorite dominant ores result from the alteration of the silicoaluminous rocks mica schists gneisses and associated felsic igneous rocks in the latter case large quantities of mg are added while na k and ca are entirely leached as documented by extensive data on the chemical composition of the rocks quartz is totally absent from the ores due to alteration into talc and by dissolution at trimouns low p al is a quasi inert component whereas a relatively high mobility is evidenced at rabenwald high p a fluid inclusion study microthermometry and leachate analyses of quartz from recrystallized pods in zones adjacent to the talc chlorite ores shows very typical solutions with similar compositions in both deposits high salinity with halite often present at room temperature relatively high ca and mg concentrations and low co 2 content leading to the alteration of the carbonates at relatively low temperatures in other respects the respective isochores confirm the pressure contrast between the two localities all these data provide constraints regarding the physical and chemical conditions of the hydrothermal alteration it is noticeable that the high salinity of the solutions seems to be an important factor in explaining the crystallization of talc and the absence of tremolite

imaging deep reflectors in the presence of signal generated noise summary in contrast to the continuous character of reflectors seen in seismic data from the sedimentary column a pervasive feature of deep crustal reflections is their laterally discontinuous nature deep reflections often appear on the seismic section as groups of flat lying or dipping segments the length of the individual segments may vary by an order of magnitude moreover the segments are often shorter than the fresnel zone for a specular reflection the apppearance of deep flat lying reflectors of this type has motivated geologic hypotheses of a layered and heterogeneous lower crust dipping bands of discontinuous reflectors are interpreted variously as decollement surfaces sutures or faults penetrating to midcrustal or deeper levels a significant geophysical concern is whether truly discontinuous reflectors in the deep crust can be distinguished from an inaccurate or incoherent image incoherence can result from the presence of signal generated noise created at the earth s surface or along the transmission path given the types of signal generated noise likely to be present in deep crustal data we wish to know how well we can resolve both laterally continuous and discontinuous reflectors using standard reflection data acquisition and processing to test the effects of such noise on the cmp stack we have conducted finite difference synthetic seismogram experiments for two similar layered models each having two specular reflectors one model contained an irregular surface layer the other contained a zone of random velocity fluctuations between the two reflectors we processed the data normally from shot gather to cmp stack and migrated section the two numerical experiments produced cmp sections with substantially different character processing the surface model data produced a clear image of the two deep reflectors as the cmp stack suppressed noise generated in the irregular surface layer the surface generated noise limited the vertical resolution as it degraded the action of predictive deconvolution applied before stack signal generated noise in the second model did not affect the deconvolution process because the scatterers were located below the zone of surface layer reverberations the laterally inhomogeneous zone degraded the image of the deepest reflector the signal generated noise in the second model may be viewed as signal reflected from the random zone the dip filtering action of the cmp stack resulted in reflection events from the random zone having greater horizontal continuity than is present in the velocity model causing further smearing by a standard time migration technique

overview of naturally occurring earth materials and human health concerns abstract the biosphere and the earth s critical zone have maintained a dynamic equilibrium for more than 3 5 billion years except for solar energy almost all terrestrial substances necessary for life have been derived from near surface portions of the land hydrosphere and atmosphere if aggregate biological activities are less than the rate of nutrient supply and or resource renewal sustained population growth is possible where the replenishment rate of a life sustaining earth material is finite usage may reach a condition of dynamic equilibrium in which biological consumption equals but on average cannot exceed the overall supply although large most natural resources are present in finite abundances for such commodities excessive present day human utilization reduces future availability and thus the ultimate planetary carrying capacity for civilization intensive use of earth materials has enhanced the quality of life especially in the developed nations still natural background levels and earth processes such as volcanic eruptions as well as human activities involving agriculture construction and the extraction refining and transformation of mineral resources have led to harmful side effects involving environmental degradation and public health hazards among naturally and anthropogenically induced risks are bioaccessible airborne dusts and gases soluble pollutants in agricultural industrial and residential waters and toxic chemical species in foods and manufactured products at appropriate levels of ingestion many earth materials are necessary for existence but underdoses and overdoses have mild to serious consequences for human health and longevity this overview briefly sketches several natural resource health hazards included are volcanic ash aerosols gases mineral dusts non volcanic aerosols nanoparticles asbestos fibrous zeolites arsenic fluorine iodine uranium thorium radium radon polonium selenium mercury copper lead chromium and cadmium also noted are health effects of natural disasters and an obligatory future sustainable consumption of natural resources not treated are the overwhelming adverse effects of malnutrition lack of potable water inadequate sanitation fossil fuel usage mining manufacturing and agricultural pollution or environmental pathogens nor are the important impacts of complex mixtures of earth materials considered with rise of the worldwide information network economic globalization and the industrial thrust of developing nations the achievement of natural resource sustainability has emerged as a strategic imperative accompanying increased rates of earth materials consumption and attendant environmental change substantially improved universal public health will require a major global effort integrating collaborations among geoscientists medical researchers and epidemiologists governments and ngos must provide important support of such cooperative efforts and both health and earth scientists must cross disciplinary and national boundaries

experimental study of dissolution rates of actinolite in cacl2 hcl h2o up to 400 c abstract actinolite dissolution rates in aqueous hcl and aqueous cacl2 hcl have been measured at temperatures ranging from 25 to 400 c at 23 mpa under conditions far from equilibrium using a flow through reactor the relative release rates for the various elements in actinolite due to breaking of metal oxygen bonds are all different all of the release rates vary with temperature and ph the release rate of si increases as temperature rises from 20 to 300 c but then decreases at higher temperatures other metallic ions such as ca mg fe and al are all released more rapidly than si at temperatures between 25 and 300 c but more slowly at temperatures 300 c the ratios of mca msi and mmg msi in the effluent at 200 c are close to the stoichiometric proportions of these elements in actinolite but differ from stoichiometric values at temperatures both above and below 200 c actinolite dissolution in aqueous hcl at 100 c yields element ratios close to stoichiometric values in the mineral but again the ratios vary at higher and lower temperatures our experiments demonstrate that under conditions far from equilibrium dissolution rates depend on both ph and the activity of aqueous mi zi where zi is the valence of the metal mi in the mineral and mi zi refers to ca2 mg2 or al3 the ion exchange model suggests that metal hydrogen ion exchange reaction on the surface is a key step for mineral dissolution and that a si rich mi deficient precursor complex is formed on the mineral surface at temperatures r a exp e a rt a h zi a mi zi where is the order with respect to the ratio of activity of hydrogen ions and dissolved metal ions mi the mg h exchange coefficient is 0 55 at 100 c the apparent activation energy ea 14 4 kj mol and a 0 23 10 3 m cm 2 s 1 our results show that water properties vary strongly within the critical region which affects the dissolution mechanism thus the release rates for various elements at temperatures above 300 c are different from those at temperatures below 300 c high resolution transmission electron microscopy hrtem and scanning electron microscopy sem studies indicate that a fe al rich si deficient layer is formed on the surface at temperatures above 300 c x ray photoelectron spectroscopy xps analyses show that the surface layer that formed by reaction with aqueous hcl at 400 c is a hydrated silicate composed of si oh and mi oh as well as si o and mi o bonds

two dimensional p t t modelling and the dynamics of extension and inversion in the betic zone se spain abstract the internal zone of the betic cordilleras offers a unique opportunity to study the dynamics of lithospheric processes at mid crustal levels which controlled the formation and evolution of the southeastern margin of iberia in this paper we present the result of two dimensional numerical modelling of p t t paths related to latest oligocene and early miocene extension and inversion in the betic zone the ages of p t t loops are constrained by an extensive data set of geothermo barometric and geochronological data including 40 ar 39 ar laser probe data we investigate the thermo mechanical evolution of the betic zone using numerical models for simple shear pure shear and combined shear the wernicke simple shear model fails to explain the observed temperatures in excess of 500 c and is not consistent with the occurrence of intrusions of ultramafic rocks in the western betics however the delaminated simple shear model with low angle faults located only at lower crustal levels is found to be consistent with the p t t data after a heating phase associated with a finite extension of 80 km rapid cooling occurred reflecting inversion of the extensional structure by nw se to n s directed compression palaeo rheological models for the latest oligocene early miocene times demonstrate the important role of the detachments produced during crustal extension for the dynamics of the subsequent inversion phase the modelling strongly suggest that inversion locked after 60 km of finite convergence after locking of the inversion overthrusting in a northward direction occurred which is compensated by pure shear deformation in the lower crust in the southeastern part of the betic zone

kinematics of cretaceous nappe tectonics in the austroalpine basement of the koralpe region eastern austria krohe a 1987 kinematics of cretaceous nappe tectonics in the austroalpine basement of the koralpe region eastern austria tectonophysicz 136 171 196 the austroalpine basement of the koralpe area austria was affected by penetrative ductile deformation in the cretaceous three metamorphic events have been established ht lp metamorphism of unknown age a hercynian mt mp metamorphism and a cretaceous eo alpine mt mp metamorphism in the koralpe area cretaceous rb sr cooling ages of muscovite indicate temperatures of at least 500 o c during the eo alpine event the most intense deformation occurred along intracrustal shear zones plattengneis north to northeast directed thrusting is indicated by an inverted metamorphic gradient regional transposition of an older foliation s c fabrics and oblique quartz fabrics after development of high temperature mylonites low angle normal shear zones low temperature mylonites cut the uppermost parts of the austroalpine basement and indicate an extensional tectonic setting at about 85 to 90 ma s c and quartz fabrics indicate downdip movements of the hanging wall towards the northeast intracrystalline a slip in quartz caused strong preferred lattice orientation in high and low temperature mylonites during the e alpine deformation the basal a slip system is more pronounced at lower temperatures whereas a prism a system predominates at higher temperatures the overall kinematic history of the austroalpine nappe complex in the study area suggests a model in which an intracrustal south over north imbrication took place in an early stage of eo alpine collision these movements were outlasted by sinistral strike slip movement possibly due to oblique collision along irregular margins of the austroalpine and brianpnnais complexes the collision imbrication process resulted in crustal thickening isostatic uplift and thus extension of the higher parts of the crust low angle normal faulting initiated sedimentation in the intramontane c tic gosau basins of late cretaceous age

cold spots during the cenozoic evolution of the eastern alps thermochronological interpretation of apatite fission track data abstract the tectonical and morphological evolution of the eastern alps during the cenozoic is discussed in the light of sedimentary record and thermochronological data of crystalline basement rocks the regional distribution of apatite fission track data in the central eastern alps reveals the differential cenozoic exhumation in contrast to the penninic of the tauern window which has been strongly uplifted and eroded since the early miocene the amount of neogene denudation was much smaller in most areas east of the hohe tauern a sudden change in the regional cooling behaviour is observed at the katschberg fault system which must have been active in post oligocene times within the austroalpine only the schladming tauern have experienced a rather strong denudation the seckau core complex east of the pols line and the area of the northern koralpe cooled to below 100 c at the end of the cretaceous and in the early eocene respectively and have never been heated again during the cenozoic these parts of the austroalpine nappe pile were always near to the surface and therefore may be summarized under the term cold spots a major post cretaceous thickening of the austroalpine can be excluded because it would have produced more uplift and erosion any remnants of miocene or older landforms are certainly not preserved in the area of the tauern window the uppermost planation surfaces in the crystalline basement at the western border of the styrian basin koralpe probably developed in the late miocene

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

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

40ar 39ar laser probe dating of detrital white micas from cretaceous sedimentary rocks of the eastern alps evidence for variscan high pressure metamorphism and implications for alpine orogeny the detritus of cretaceous synorogenic sandstones of the northern margin of the austroalpine microplate contains evidence for a high pressure metamorphic basement and obducted oceanic crust exposed in early alpine time 40 ar 39 ar laser probe data of detrital white micas give excellent plateau ages in a narrow range from 320 to 360 ma white micas cover the whole range from muscovites up to phengites 3 04 to 3 48 si per formula unit heavy mineral spectra contain chrome spinel glaucophane chloritoid epidote and garnet as well as zircon tourmaline and rutile glaucophane chloritoid and phengite correlate in their abundance these minerals also correlate positively with the stable minerals zircon tourmaline and rutile derived from continental rock and negatively with chrome spinel which represents oceanic crustal provenance we propose that both glaucophane and phengite come from the same source rock variscan high pressure metamorphic rocks of the austroalpine basement the early carboniferous age gives constraints for paleogeographic models concerning the collision between gondwana and laurussia furthermore detrital glaucophane in the early alpine sedimentary rocks cannot be used as proof for cretaceous subduction at the austroalpine penninic plate boundary

thermometrically inferred cooling rates from the plattengneis koralm region eastern alps abstract closure of fe mg exchange between garnet and biotite is used to estimate cooling rates from the koralm region of the austro alpine nappe complex east of the tauern window in the eastern alps maximum cooling rates for a 700 m thick mylonitic shear zone the plattengneis are at least an order of magnitude higher than those of surrounding country rocks the cooling rate history inferred for the plattengneis suggests exponentially decreasing cooling rates whilst the cooling history of the surrounding country rocks is inferred to involve an approximately constant cooling rate the fast cooling rates in the shear zone are interpreted as evidence for an additional energy input from an internal heat source which may have been heat that was released during deformation related to the alpine nappe stacking processes

a lithospheric cross section through the swiss alps ii constraints on the mechanical structure of a continent continent collision zone summary the calculation of strength profiles along the european geotraverse egt through the swiss alps yields constraints on the large scale vertical and lateral mechanical structure through the alpine continent continent collision zone strength profiles are evaluated for different assumptions on petrological stratification and strain rate and are based on temperature depth profiles derived from transient thermo kinematic modelling of the neoalpine orogeny the main contribution to the total strength results from the mantle lithosphere which is strongly controlled by temperature in contrast the crustal contribution is mainly determined by variations in petrological stratification a direct correlation between surface heat flow and the total strength of the crust the mantle lithosphere and the entire lithosphere crust and mantle lithosphere is not observed our results demonstrate that in tectonically active areas a transient thermal model along with detailed knowledge of the deep structure and petrology is necessary to evaluate lithospheric strength envelopes inside the collision zone strain rate has a strong control on the bottom of the mechanically strong crust whereas outside the collision zone the effect is less significant the cut off depth of seismicity along the profile which correlates largely with the bottom of the mechanically strong crust deviates from the 300 400 c isotherm the inferred effective elastic thickness for the molasse basin north of the alps is in agreement with flexural modelling results whereas for the southern alps the predictions deviate

p t t history of the lower austroalpine nappe complex in the tarntaler berge nw of the tauern window implications for the geotectonic evolution of the central eastern alps new petrologic and 40ar 39ar geochronologic data constrain conditions of alpine metamorphism along the northwestern border of the tauern window the p t estimations based on phengite barometry were determined for samples from units of the lower austroalpine nappe complex exposed above the southpenninic interior of the tauern window and from upper parts of the southpenninic bundner schiefer sequence results suggest that both mesozoic metasedimentary nappe units reckner and hippold nappes and an ophiolitic nappe reckner complex of the lower austroalpine nappe complex have been metamorphosed at pressures between 8 and 10 5 kbar and temperatures around 350 c the structurally highest lower austroalpine unit quartzphyllite nappe was not affected by high pressure metamorphism and records maximum p t conditions of approximately 4 kbar and 400 c highest parts of the structurally underlying southpenninic bundner schiefer sequence were metamorphosed at intermediate pressures 6 7 kbar temperatures increased in all structural units during decompression whole rock 40ar 39ar plateau ages of silicic phyllites and cherts with abundant high si phengites record ages around 50 ma in the reckner nappe and 44 37 ma in the hippold nappe and southpenninic bundner schiefer sequence these ages are interpreted to date closely the high pressure metamorphism

heat sources of cretaceous metamorphism in the eastern alps a discussion abstract the alpine orogenic cycle is characterised by a series of early metamorphic events that occurred in the cretaceous the eoalpine events a collection of data on peak metamorphic conditions pt paths and on relationships between structure and metamorphism for these events in the eastern alps shows that 1 eoalpine metamorphism occurred largely simultaneously with pervasive deformation 2 the eoalpine thermal peak was reached near the pressure peak 3 lower grade structurally higher rocks reached their metamorphic peak earlier than higher grade structurally lower rocks and there is a wide spread of metamorphic ages 4 low grade metamorphic conditions are probably more perturbed than high grade conditions and 5 there is a conspicuous regional distribution of metamorphic grade with amphibolite and eclogite facies metamorphism occurring predominantly in two regions located symmetrically west and east of the tauern window possible heating mechanisms are discussed that can satisfy these observations and a review of previous thermal models is provided it is shown that models which rely on conductive heat transfer cannot account for all of these observations in order to assess other heat sources the effects of shear heating are evaluated here with simple model calculations and a straightforward comparison of length and time scales of dissipative heat production the results suggest that shear heat episodically released during the stacking of the austroalpine nappe pile may be a significant contributor to the observed thermal perturbation

the stacking of thrust slices in collision zones and its thermal consequences the thermal consequences of stacking up thrust slices in collision zones are investigated using simple one dimensional thermal models the metamorphic evolution geotherms and p t time paths of a given tectonic unit belonging to a crustal stacking wedge made of more than two units is governed by three effects cooling and pressure decrease associated with erosion cooling by the lowest units screen effect heating by the upper units cover effect it is shown that the efficiency of these effects are dependent on the tectonic evolution of the collision zone the metamorphic evolutions are very sensitive to the following tectonic parameters the number of thrusted units involved in thickening the time delay between each thrust and finally the mode of stacking of the different units over and understacking it appears that for a given depth of burial the temperature increase during uplift is less important in a crust thickened by three or four units than in the case of two units the screen effect during understacking is more efficient for a short time delay 10 ma between each thrust overstacking leads to higher temperatures before uplift when compared to understacking it is also shown that the thermal perturbation induced in an intermediate unit of the pile is more efficiently recorded when its thickness is rather small 10 km it is shown that for an erosion controlled uplift the shape of the p t t path depends on the position of the rocks within a given unit and on the unit position within the pile finally the general metamorphic evolutions during crustal thickening hp lt metamorphism and subsequent overprint are discussed in terms of the previously mentioned parameters in the case of the western alps it appears that the more or less efficient greenschist overprint of the units involved in thickening can be explained by different time intervals between the thrust events

archimedes revisited a structural test of eclogite emplacement models in the austrian alps high pressure rocks of the eclogite zone tauern window eastern alps formed at 20 kb 600 c uplift was fast without post burial heating extensive near field and far field deformation of the eclogite zone and its surroundings provide evidence for a tectonic uplift mechanism published emplacement models buoyant rise underplating and extension wrench faulting create distinct patterns of crustal deformation and are therefore testable by structural analysis we show that emplacement related deformation and its kinematics are consistent with underplating and extension extension is two phased the first phase may be driven by changes in rate or direction of plate convergence the second phase is due to large scale underplating of continental crust

thermomechanical consequences of cretaceous continent continent collision in the eastern alps austria insights from two dimensional modeling we use two dimensional numerical modeling techniques to investigate the thermomechanical consequences of closure of the meliata hallstatt ocean and consequent cretaceous continent continent collision in the eastern alps austria in the modeling a lower plate position of the austro alpine aa continental block is adopted during collision with the upper juvavic silice block the thermal structure of the lithosphere was calculated for major aa tectonic units upper middle and lower austro alpine by integration of the transient heat flow equation along an approximately nw se cross section east of the tauern window indications of the rheological evolution of the aa were determined by calculating strength profiles at key stages of the cretaceous orogeny making use of the thermal modeling predictions combined with rock mechanics data cooling in the upper plate and lower greenschist facies metamorphism within footwall parts of the lower upper austro alpine ua plate related to se directed underthrusting of the ua beneath the upper juvavic silice block at circa 100 ma were predicted by the numerical model the observed pressure temperature path for deeply buried middle austro alpine ma upper crustal units and their subsequent isothermal exhumation are best reproduced assuming a pressure peak at 95 ma and exhumation rates ranging between 4 and 7 5 mm yr 1 from the modeling results we deduce that the temperature evolution during eclogite exhumation is primarily dependent on rates of tectonic movements and largely independent of the mode of exhumation thrusting versus erosion furthermore very rapid postmetamorphic exhumation of southern lower austro alpine la units is predicted in order to account for subsequent cooling this is constrained by 40ar 39ar data the cooling paths of ma and la rocks appear to be primarily controlled by their near surface positions at the end of the cretaceous rather than by other processes such as concurrent underthrusting upward advection of heat by rapid exhumation induced thermal weakening of the thickened crust the inferred weakness of the central parts of the orogenic system may play an important role during detachment related tectonic unroofing orogenic collapse and concomitant basin formation central alpine gosau basins

climate induced rebound and exhumation of the european alps foreland basins record the regional isostatic compensation of mountain belts during periods of crustal thickening they subside and when erosion unloads the mass of the mountains the basins rebound and are eroded in order to evaluate this mechanism for rebound it is critical that the timing and magnitude of erosion are documented we present data estimating the timing and magnitude of late orogenic or postorogenic erosion in the north alpine foreland basin of switzerland mineral cooling ages demonstrate that the basin underwent 1 3 km of erosion soon after 5 ma this erosion coincided with a decline in structural deformation in the swiss alps and a doubling of sediment accu mulation rates in surrounding depocenters we propose that accelerated erosional un roofing of the swiss alps triggered isostatic rebound and erosion of the foreland basin after 5 ma a projection of the isostatic rebound of the basin into the mountains suggests that at least 6 5 km of erosion should have occurred in the high topography of the aar massif accelerated erosion in the swiss alps at that time is explained by an increase in atmospheric moisture driven by an intensification of the atlantic gulf stream at 4 6 ma consequently we propose that the changing erosional capacity of the climate triggered late orogenic to postorogenic mass reduction and isostatic rebound of the swiss alps and their neighboring foreland basin

40ar 39ar geochronology and p t t paths from the cordillera darwin metamorphic complex tierra del fuego chile ar 39ar data collected from hornblende muscovite biotite and k feldspar constrain the p t t history of the cordillera darwin metamorphic complex tierra del fuego chile these data show two periods of rapid cooling the first between c 500 and c 325 c at rates 225 c ma and the second between c 250 and c 200 c for high t cooling 40ar 39ar ages are spatially disparate and depend on metamorphic grade rocks that record deeper and hotter peak metamorphic conditions have younger 40ar 39ar ages sillimanite and kyanite grade rocks in the south central part of the complex cooled latest 40ar 39ar hbl 73 77 ma ms 67 70 ma bt 68 ma and oldest kfs 65 ma thermobarometry and p t path studies of these rocks indicate that maximum burial of 26 30 km at 575 625 c may have been followed by as much as 10 km of exhumation with heating of 25 50 c staurolite grade rocks have intermediate 40ar 39ar ages hbl 84 86 ma ms 71 ma bt 72 75 ma and oldest kfs 80 ma thermobarometry on these rocks indicates maximum burial of 19 26 km at temperatures of 550 580 c garnet grade rocks have the oldest ages ms 72 ma and oldest kfs 91 ma peak p t conditions were 525 550 c and 5 7 kbar regional metamorphic temperatures for greenschist facies rocks south of the beagle channel did not exceed c 300 325 c from 110ma to the present although the rocks are only 2 km from kyanite bearing rocks to the north one dimensional thermal models allow limits to be placed on exhumation rates assuming a stable geothermal gradient of 20 25 c km i the maximum exhumation rate for the st grade rocks is c 2 5 mm yr i whereas the minimum exhumation rate for the ky sil grade rocks is c 1 0 mm yr uniform exhumation rates cannot explain the disparity in cooling histories for rocks at different grades and so early differential exhumation is inferred to have occurred petrological and geochronological comparisons with other metamorphic complexes suggest that single exhumation events typically remove less than c 20 km of overburden this behaviour can be explained in terms of a continental deformation model in which brittle extensional faults in the upper crust are rooted to shallowly dipping ductile shear zones or regions of homogeneous thinning at mid to deep crustal levels the p t r data from cordillera darwin 1 are best explained by a wedge extrusion model in which extensional exhumation in the southern rear of the complex was coeval with thrusting in the north along the margin of the complex and into the magallanes sedimentary basin 2 suggest that differential exhumation occurred initially with st grade rocks exhuming faster than ky sil grade rocks and 3 show variations in cooling rate through time that correlate both with local deformation events and with changes in plate motions and interactions

mantle lithospheric deformation and crustal metamorphism with some speculations on the thermal and mechanical significance of the tauern event eastern alps changes in the thickness of the mantle lithosphere beneath convergent orogens through processes such as the pervasive thickening of the lithosphere and the convective thinning of the thermal boundary layer dictate the heat flow through the base of the crust and thus may profoundly influence the thermal evolution of crustal metamorphic terrains calculations based on one dimensional thermal energy balances show that when mantle lithosphere is substantially thickened and remains intact through the orogenic cycle then low temperature facies series including blueschist and eclogite facies may be preserved throughout the crust in contrast crust thickened above attenuated mantle lithosphere will develop much higher temperature facies series potential energy arguments suggest that changes in the thickness in the mantle lithosphere induce changes in the elevation and the potential energy stored within the lithosphere therefore the response to mantle lithospheric deformation observable in crustal metamorphic terrains should not only be recorded in the thermal regime but also in changes in the incremental strain history in as much as it reflects the force balance operating within the orogen for example mantle lithospheric thinning beneath thickened crust may cause an increase in crustal temperatures synchronous with the termination of convergent strain or for large reductions in mantle lithospheric thickness with the onset of extensional deformation such histories are recorded in a number of young metamorphic terrains for example the eastern alps which may provide an important thermal and isostatic record of the mantle lithospheric response to convergent deformation here we show how application of these ideas may lead to new insights into some outstanding problems concerning the thermal and mechanical evolution of the eastern alps during the tertiary tauern metamorphic event

subcrustal tectonic erosion in orogenic belts a model for the late cretaceous subsidence of the northern calcareous alps austria analysis of the upper cretaceous to eocene gosau group of the northern calcareous alps austria indicates rapid subsidence after a short interval of deformation uplift and erosion reconstructions of basement subsidence of 3000 m from the late turonian 89 ma onward show a distinct shift of the deformation and subsidence from the northwest to the southeast together with a tilting of the northern calcareous alps toward the north comparison with recent analogues suggests that subcrustal tectonic erosion due to the subduction of a topographic high of the south penninic ocean may be the cause for this subsidence pattern tectonic erosion along ancient plate margins can be recognized by deformation and widespread erosion followed by regional subsidence not related to extension or flexural loading

pressure temperature time evolution of the high pressure metamorphic complex of sifnos greece model studies of continental collision tectonics and pressure temperature time p t t predictions quantitatively demonstrate the key role of synsubduction uplift in the preservation of blueschist and eclogite facies metamorphic rocks rheological stratification of the subducting lithosphere allows development of detachment faults at the compositional boundary between the upper and lower crust material of supracrustal continental affinity is subducted to depths in excess of 50 km and then delaminated from the downgoing slab subduction continues while the detached domain is uplifted independently from the newly active hanging walls and footwalls two dimensional thermal calculations indicate that the nearby active subduction provides the cooling mechanism required to preserve blueschists and eclogites whereas the differential motions of the independently uplifted domains can explain the observed heterogeneity in p t t pathways with some domains displaying a greenschist overprint

timing of metamorphism in the tauern window eastern alps rb sr ages and fabric formation the peripheral schieferhulle of the tauern window of the eastern alps represents post hercynian penninic cover sequences and preserves a record of metamorphism in the alpine orogeny without the inherited remnants of hercynian events that are retained in basement rocks the temperature time deformation history of rocks at the lower levels of these cover sequences have been investigated by geochronological and petrographic study of units whose p t evolution and structural setting are already well understood the eclogite zone of the central tauern formed from protoliths with penninic cover affinities and suffered early alpine eclogite facies metamorphism before tectonic interposition between basement and cover it then shared a common metamorphic history with these units experiencing blueschist facies and subsequent greenschist facies conditions in the alpine orogeny the greenschist facies phase associated with penetrative deformation in the cover and the influx of aqueous fluids reset sr isotopes in metasediments throughout the eclogite zone and cover schists recording deformation and peak metamorphism at 28 30 ma the peripheral schieferhulle of the south east tauern window yields rb sr white mica ages which can be tied to the structural evolution of the metamorphic pile early prograde fabrics pre date 31 ma and were reworked by the formation of the large north east vergent sonnblick fold structure at 28 ma peak metamorphism post dated this deformation but by contrast to the equivalent levels in the central tauern peak metamorphic conditions did not lead to widespread homogenization of the sr isotopes localized deformation continued into the cooling path until at least 23 ma partially or wholly resetting sr white mica ages in some samples these isotopic ages may be integrated with structural data in regional tectonic models and may constrain changes in the style of crustal deformation and plate interaction however such interpretations must accommodate the demonstrable variation in thermal histories over small distances

elastic finite difference modelling of lower crustal reflections it is a common feature to observe on deep reflection profiles short less than the fresnel area diameter and strongly discontinuous lower crustal reflections such wave patterns can be attributed to variations in the crustal properties on the scale of a few wavelengths in order to explain these characteristics we have computed finite difference synthetic seismograms for various types of deep heterogeneities focusing defocusing and interference effects were especially studied the results can only be interpreted in a qualitative manner because our models exhibit departures from the real cases lower frequency content and only two dimensional structures it is found that simple undulations of the deep interfaces can hardly produce the discontinuous pattern observed but high velocity intrusions generate complex interferences matching the reflection character of real data furthermore the reflection patterns strongly depend both on length and shape of the inclusions

subduction tectonic erosion and late cretaceous subsidence along the northern austroalpine margin eastern alps austria abstract the late cretaceous to early tertiary subsidence history of the northern calcareous alps nca records the effect of two independent basin formation mechanisms at the northern leading margin of the austroalpine unit the terrestrial to shallow marine sediments of the lower gosau subgroup were deposited mainly within small fault bound basins during a phase of strike slip faulting from the late turonian onwards after a short period of uplift deformation and erosion of 1 to 3 ma renewed rapid subsidence followed during this period the whole nca subsided into bathyal to abyssal depths the characteristics of this second evolutionary phase are 1 a short period of uplift and erosion followed by strong subsidence of the whole nca with tectonic subsidence rates up to 700 m ma 2 sedimentation of turbidites and hemipelagites upper gosau subgroup 3 northward tilting of the depositional area 4 elimination of an accretionary wedge north of the nca as the main source for the sediments and 5 a pronounced migration of the subsidence event from the northwest to the southeast from late turonian santonian to the maastrichtian these features can be explained by a model of subduction tectonic erosion along the northern margin of the austroalpine unit a part of the adriatic microplate tectonic erosion as compared to recent analogues and fore arc modelling may be due to the collision and oblique subduction of an oceanic swell or ridge of the penninic plate beneath the overriding austroalpine unit with the nca on its leading northern margin

alpine geodynamic evolution of passive and active continental margin sequences in the tauern window eastern alps austria italy a review the penninic oceanic sequence of the glockner nappe and the foot wall penninic continental margin sequences exposed within the tauern window eastern alps have been investigated in detail field data as well as structural and petrological data have been combined with data from the literature in order to constrain the geodynamic evolution of these units volcanic and sedimentary sequences document the evolution from a stable continent that was formed subsequent to the variscan orogeny to its disintegration associated with subsidence and rifting in the triassic and jurassic the formation of the glockner oceanic basin and its consumption during the upper cretaceous and the paleogene these units are incorporated into a nappe stack that was formed during the collision between a penninic zentralgneis block in the north and a southern austroalpine block the venediger nappe and the storz nappe are characterized by metamorphic jurassic shelf deposits hochstegen group and cretaceous flysch sediments kaserer and murtorl groups the eclogite zone and the rote wand modereck nappe comprise permian to triassic clastic sequences wustkogel quartzite and remnants of platform carbonates seidlwinkl group as well as jurassic volcanoclastic material and rift sediments brennkogel facies covered by cretaceous flyschoid sequences nappe stacking was contemporaneous to and postdated subduction related high pressure eclogite and blueschist facies metamorphism emplacement of the eclogite bearing units of the eclogite zone and the glockner nappe onto penninic continental units zentralgneis block occurred subsequent to eclogite facies metamorphism the eclogite zone a former extended continental margin was subsequently overridden by a pile of basement cover nappes rote wand modereck nappe along a ductile out of sequence thrust low angle normal faults that have developed during the jurassic extensional phase might have been inverted during nappe emplacement