the dav and periadriatic fault systems in the eastern alps south of the tauern window alpine deformation of austroalpine units south of the tauern window is dominated by two kinematic regimes prior to intrusion of the main periadriatic plutons at 30 ma the shear sense was sinistral in the current orientation with a minor north side up component sinistral shearing locally overprints contact metamorphic porphyroblasts and early periadriatic dykes direct rb sr dating of microsampled synkinematic muscovite gave ages in the range 33 30 ma whereas pseudotachylyte locally crosscutting the mylonitic foliation gave an interpreted 40ar 39ar age of 46 ma the transition from sinistral to dextral transpressive kinematics related to the periadriatic fault occurred rapidly between solidification of the earlier dykes and of the main plutons subsequent brittle ductile to brittle faults are compatible with n s to nnw sse shortening and orogen parallel extension antithetic riedel shears are distinguished from the previous sinistral fabric by their fine grained quartz microstructures with local pseudotachylyte formation one such pseudotachylyte from speikboden gave a 40ar 39ar age of 20 ma consistent with pseudotachylyte ages related to the periadriatic fault the magnitude of dextral offset on the periadriatic fault cannot be directly estimated however the jump in zircon and apatite fission track ages establishes that the relative vertical displacement was 4 5 km since 24 ma and that movement continued until at least 13 ma

palinspastic reconstruction and topographic evolution of the eastern alps during late tertiary tectonic extrusion this paper presents a new palinspastic restoration of the eastern alps for neogene time and an attempt to reconstruct the neogene palaeogeology palaeotopography and palaeohydrography in connection with the structural evolution the eastern alps underwent radical horizontal displacement during the neogene due to large strike slip systems and formation of structural windows our palinspastic reconstruction considers a the rearrangement of tectonic units dismembered during tectonic extrusion b the tectonic denudation driven by displacement of the crystalline blocks c geochronological arguments and d the sedimentary record of the syn extrusion basins the rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre miocene unstretched pattern of the eastern alps reduced to 65 of its present day e w elongation using this structural frame and considering the sedimentary record a set of palaeogeologic and palaeotopographic sketch maps with the palaeo river systems is presented for three time slices pre syn and post extension situation in late oligocene and early miocene times the western eastern alps were already mountainous whereas the eastern part of the orogen formed lowlands or hilly areas enhanced block movement in the course of the extrusion process around the early middle miocene boundary led to the formation of intramontane sedimentary basins and a fault induced reorientation of the drainage pattern which forms the basis of the modern river system in the area east of the tauern window this region where pre miocene land surfaces are preserved probably became a mountainous area not before late miocene time and never reached the elevations of the areas further west

carbo permian pteridophyll leaf fragments from an amphibolite facies basement tauern window austria graphitic schists from the pennine basement tauern window austria contain fragments of pteridophyll leaves they are preserved despite the overall strong deformation and metamorphism at amphibolite facies conditions 525 c 750 100 mpa due to a particular strain path with volume loss by pressure solution they were determined as cf callipteridium sp indicating a permo carboniferous age this depositional age is similar to radiometric age data obtained for the intrusion of nearby metagranitoids indicating either tectonic contacts between the metagranitoids and the graphite schists or a very active and rapidly changing tectonic regime during the hercynian event

the kinematics of movements along the insubric line and the emplacement of the ivrea zone schmid sm zingg a and handy m 1987 the kinematics of movements along the insubric line and the emplacement of the ivrea zone in h j zwart m martens i van der molen c w passchier c spiers and r l m vissers editors tectonic and structural processes on a macro meso and micro scale tecta a hys 135 47 66 the insubric line west of locamo is characterized by a 1 km thick greenschist facies mylonite belt east of locamo these mylonites are overprinted by a discrete brittle fault the mylonites are derived from basement units of the central alps sesia zone and the southern alps ivrea zone as well as from the permo mesozoic cover of the southern alps canavese sense of shear criteria indicate that the mylonites accomm ated backt s g followed by dextral strike slip motion mylonitization during backtbrusting was synchronous with backfolding of the central alpine nappes under higher metamorphic conditions a horizontal temperature gradient resulted from the rapid juxtaposition of the warm central alpine block against the cold southern alpine block mylonites formed during the later dextral strike slip event are related to large transcurrent displacements in the central alps deduced from regional kinematic considerations thus both mylo t ation events are contempor eous with deformation to the north and south of the insubric line insubric phase extensively modifying the pre insubric crustal configuration of the alps the insubric phase post dates the bergell intrusion 30 m y the emplacement of the geophysical ivrea body is a combined effect of vertical uplift due to e w directed crustal thinning during the early jurassic and underplating by continental crust associated with late cretaceous compression a deep crustal normal fault pogallo line subsequently rotated during tertiary alpine orogenesis separates deeper parts of the southern alpine crust ivrea zone from intermediate crustal levels strona ceneri zone the rigid ivrea body localir ed large strains within the insubric mylonite belt and is responsible for the present curvature of the insubric line in uetion

grain size effects on the closure temperature of white mica in a crustal scale extensional shear zone implications of in situ 40ar 39ar laser ablation of white mica for dating shearing and cooling tauern window eastern alps abstract in situ 40ar 39ar laser ablation dating of white mica grains was performed on samples from the footwall of a crustal scale extensional fault katschberg normal fault knf that accommodated eastward orogen parallel displacement of alpine orogenic crust in the eastern part of the tauern window this dating yields predominantly cooling ages ranging from 31 to 13 myr with most ages clustering between 21 and 17 myr folded white micas that predate the main katschberg foliation yield within error the same ages as white mica grains that overgrow this foliation however the absolute ages of both generations are older at the base 20 myr where their grain size is larger 300 500 m than at the top and adjacent to the hangingwall 17 myr of this shear zone where grain size is smaller

the arcs of the western alps and the northern apennines an updated view abstract the arcs of the western alps and the northern apennines and the link between them are in the process of being investigated using the european geotraverse and they have historically been interpreted in many different ways new information particularly geophysical further constrains possible models both arcs have evolved in several stages sometimes complexly interrelated and sometimes independent of each other compressional belts produced in these stages have either been of the push arc type indentation into a deformable mass or the pull arc type backward migration of hinge of a subduction zone leading to small extensional basins known as back arc basins and pores with an arcuate mountain range on the subduction side extensional periods with the possible formation of pull arcs in the alps comprise the gosau period between the eo and meso alpine push arc phases and the oligocene lull period between the meso and the neo alpine push arc phases in the northern apennines remainders of the meso alpine nappes were involved in oligocene early miocene pull arc formation associated with spreading in the balearic sea followed by push arc formation particularly in the middle miocene and by renewed pull arc formation from the latest late miocene to the present during all of these developments the moho was modified by such processes as lithospheric stretching asthenospheric intrusions subhorizontal shearing and isostatic uplift the present moho configuration is consequently a collage of moho patches formed at different intervals both push and pull arcs are laterally bounded by complementary strike slip or transform zones these too were modified in the course of history and their final geometry is consequently of a very complex nature in the alps for instance the insubric fault zone appears to have been the main dextral transform fault of the neogene push arc until it was sinistrally kinked by the giudicarie fault zone and probably deactivated dextral transpression being briefly transferred to the en echelon brachyanticlines of the late alpine windows in the case of the oligocene apennines the sinistral rotations of corsica and sardinia otherwise hard to understand may be attributed in part to sinistral transform motions along the eastern border zone of the oligocene early miocene balearic extension

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

kinematics of the inntal shear zone sub tauern ramp fault system and the interpretation of the transalp seismic section eastern alps austria abstract a new interpretation of the inntal tauern sector of the transalp seismic section is presented one of the most prominent contrasts in reflectivity in the transalp seismic section is the contact between the bajuvaric unit in the footwall and the overlying tirolic unit and its basement across a moderately south dipping interface we trace this contact from the surface at the southern margin of the inn valley to a depth of 5 km there the contact is deformed or cut by the tauern window northern margin we define the contact between bajuvaric and tirolic units as brixlegg thrust which is older than miocene tauern window exhumation and has a paleogene age the sub tauern ramp connects with the inntal fault system at the surface and roots below the tauern window oblique thrust movements across this fault system in the miocene caused exhumation of the hanging wall where the fault has a ramp geometry which is in the area of the transalp cross section and west of it east of the transalp cross section the fault system merges with alpine basal thrust which is a flat no miocene exhumation occurred above the flat

wave current interaction in willapa bay 1 this paper describes the importance of wave current interaction in an inlet estuary system the three dimensional fully coupled coupled ocean atmosphere wave sediment transport coawst modeling system was applied in willapa bay washington state from 22 to 29 october 1998 that included a large storm event to represent the interaction between waves and currents the vortex force method was used model results were compared with water elevations currents and wave measurements obtained by the u s army corp of engineers in general a good agreement between field data and computed results was achieved although some discrepancies were also observed in regard to wave peak directions in the most upstream station several numerical experiments that considered different forcing terms were run in order to identify the effects of each wind tide and wave current interaction process comparison of the horizontal momentum balances results identified that wave breaking induced acceleration is one of the leading terms in the inlet area the enhancement of the apparent bed roughness caused by waves also affected the values and distribution of the bottom shear stress the pressure gradient showed significant changes with respect to the pure tidal case during storm conditions the momentum balance in the inlet shares the characteristics of tidal dominated and wave dominated surf zone environments the changes in the momentum balance caused by waves were manifested both in water level and current variations the most relevant effect on hydrodynamics was a wave induced setup in the inner part of the estuary

changing patterns of exhumation and denudation in front of an advancing crustal indenter tauern window eastern alps the changing shape of indenting crustal blocks during northward motion of the adriatic microplate induced migration of miocene doming and orogen parallel extension of orogenic crust in the tauern window new structural and kinematic data indicate that initial shortening of the penninic nappe pile in the tauern window by upright folding and strike slip faulting was transitional to coeval north south shortening and east west extension the latter was accommodated by normal faulting at the eastern and western margins of the window retrodeforming these post nappe structures in map view yields a map view reconstruction of the orogenic crust back to 30 ma including the onset of pronounced indentation at 21 ma this model supports the notion that indentation involved approximately equal amounts of north south shortening and orogen parallel stretching and extrusion toward the pannonian basin as measured from the indenter tip to the european foreland in the north and austroalpine units in the east comparison of areal denudation of the orogenic crust before and after indentation indicate that erosion associated with upright folding was the primary agent of denudation whereas extensional unroofing and limited erosion along normal faults at the eastern and western ends of the tauern window accounted for only about a third of the total denudation

the northern giudicarie and the meran mauls fault alps northern italy in the light of new paleomagnetic and geochronological data from boudinaged eo oligocene tonalites this study concentrates on small intrusions along two important faults of the giudicarie fault system the northern giudicarie and the meran mauls fault summarised under the term tonalitic lamellae magnetic fabric analyses in combination with structural field data indicate dextral strike slip deformation along the ne sw striking northern part of the giudicarie fault system the meran mauls fault overprinted by younger thrusting the regional stressfield was oriented approximately nnw sse during tertiary times the distinctive change in deformation along the meran mauls fault from dextral strike slip to top se thrusting may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal magnetic foliation based on the assumption of a preliminary straight periadriatic lineament bent by the nnw wards advancement of the southalpine indenter the tonalitic lamellae may be interpreted as lenses sheared off from the adamello batholith during indentation new u pb data on zircon show that some of the lamellae are of oligocene rupelian others of late eocene priabonian age an amphibole gabbro lens occurring on the meran mauls fault provides a middle eocene bartonian age among the major periadriatic plutons only the southern units of the adamello batholith also intruded in the eocene that suggests a strong correlation between the tonalitic lamellae and the adamello batholith the analyses of the remanent magnetisation and the curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures this indicates slow cooling of the investigated intrusions along the giudicarie fault system down to approximately 300 c which is in contrast to the fast cooling determined for the adamello intrusion units currently at the surface the new zircon fission track data also show later cooling of the tonalites along the giudicarie fault system when compared with the adamello batholith in the south and the mauls lamellae in the north indicating that this area contains magmatic bodies exhumed from a deeper structural level than in the adamello and the mauls region this may be due to important top se thrusting and transpressive faulting in the footwall of the northern giudicarie fault and the meran mauls fault

structural evolution of the rieserferner pluton in the framework of the oligo miocene tectonics of the eastern alps abstract the structural evolution of the oligocene rieserferner pluton eastern alps developed during pluton cooling and exhumation includes localized deformation structures consisting of i steeply dipping joints leucocratic dykes and quartz feldspar veins and related ductile shear zones formed at 600 c ii shallowly dipping joints with associated epidote and quartz veins and related ductile shear zones 450 c iii steeply dipping mafic dykes and calcite white mica bearing brittle ductile faults 300 c iv steeply dipping pseudotachylyte bearing faults

lateral extrusion in the eastern alps part 1 boundary conditions and experiments scaled for gravity lateral extrusion encompasses extensional collapse gravitational spreading away from a topographic high in an orogenic belt and tectonic escape plane strain horizontal motion of wedges driven by forces applied to their boundaries in the eastern alps it resulted from 1 an overall northerly compression apulia against eurasia 2 a strong foreland bohemian massif 3 lack of constraint along a lateral boundary carpathian region and 4 a previously thickened gravitationally unstable thermally weakened crust eastern alpine orogenic belt six indentation experiments reproduce lateral extrusion at lithospheric scale the models have two to four lithospheric layers with a mohr coulomb rheology for the upper and a viscous rheology for the lower crust the lithosphere rests upon a low viscosity asthenosphere a broad indenter a narrow deformable area and a weakly constrained eastern margin fullfill as closely as possible conditions in the eastern alps indentation produces both thickening in front of the indenter and escape of triangular wedges lateral variations in crustal thickness become attenuated by gravitational spreading the overall fault pattern includes domains of reverse strike slip oblique normal and pure normal faults strike slip faults in conjugate sets develop serially the narrow width of the deformable area and the strength of the foreland determine the angles between the sets gravitational spreading produces a rhombohedral pattern of oblique and pure normal faults along the unconstrained margin opposite the unconstrained margin the indenter front shows thrusts and folds intersecting with the conjugate strike slip sets a triangular indenter favors spreading high velocity of indentation favors escape high confinement limits lateral motion inhibits spreading and favors thickening lateral extrusion in the eastern alps is best modeled by 1 a weak lateral confinement 2 a broad and straight indenter 3 a narrow width of the deformable area and 4 a rigid foreland crustal thickening lateral escape and gravitational spreading all contribute to the overall deformation

three dimensional insight into central alpine collision lower plate or upper plate indentation accommodation of collisional shortening in the central alps varies dramatically along strike and this change is inferred to result from along strike changes of rheology in the western central alps 90 of shortening is accommodated in the thickened lower plate in the eastern central alps 90 of shortening is accommodated in the upper plate in the central central alps shortening is almost equally partitioned between the two plates the lower crust of the adriatic plate forms a wedge that reaches a maximum north south extension of almost 70 km in the engadine section progressively decreasing westward and disappearing along the simplon section this difference indicates an along strike increase of intra plate decoupling limiting shortening of the adriatic plate to the middle and upper parts of the crust whereas the upper plate indents into the thickened accreted lower plate in the simplon section it is the lower plate that indents an intensely deforming upper plate in the engadine section in the west the ivrea mantle body increases the strength of the adriatic upper plate and barrovian metamorphism weakens the lower plate therefore along strike transfer of shortening from one plate to the other appears to be a manifestation of along strike changes in rheology deep in the crust

the tertiary dynamics of the northern eastern alps austria changing palaeostresses in a collisional plate boundary abstract six tertiary deviatoric palaeostress tensor groups from 165 stations in the calcareous alps describe the upper crustal dynamics of the leading edge of the adriatic plate during protracted continental collision with the european lower plate palaeostress changes are correlated to the kinematic evolution of the plate boundary and to independently derived plate kinematic data of the alpine carpathian pannonian area each palaeostress direction is defined by 32 to 89 individual tensors which constrain 1 late eocene to oligocene nw directed compression during thrusting and dextral shearing on wnw striking faults nw directed compression along the northern margin of the adriatic plate is correlated to its n directed translation combined with a counterclockwise rotation 2a late eocene to early miocene n directed compression during n directed thrusting of penninic and helvetic units and the molasse 2b early to middle miocene n directed strike slip compression during the onset of eastward lateral extrusion the change from nw to n directed compression is interpreted to result from strain partitioning at the periadriatic fault which has formed the new adriatic plate boundary since the oligocene dextral shearing on this fault accommodated continued anticlockwise rotation and decoupled the northern eastern alps from the rotational component n directed compression in the calcareous alps paralleled the n directed translation of the adriatic plate 3 middle miocene ne directed compression of thrust and strike slip type during lateral extrusion ne directed compression in the calcareous alps resulted from the drag of the eastward extruding central eastern alps sinistral shear stress was transmitted across the ene trending salzach ennstal fault ne oriented 1 axes include 45 with the e w striking zone of distributed sinistral shear in the calcareous alps 4 middle miocene e directed extension associated with orogen parallel normal faulting of the central eastern alps e directed extension paralleled the direction of mass transfer towards the pannonian basin during lateral extrusion normal faulting was induced by reduced lateral confinement due to removal of material east of the alps on the large scale eastward motion was enabled by the e directed retreat of the eastern carpathian subduction zone 5 late miocene e directed compression orogen parallel compression obstructed lateral extrusion the stress change from extension to e directed compression was caused by the end of subduction retreat in the eastern carpathians due to dynamic changes in the subduction zone 6 n directed extension late to post miocene extension paralleled recent topographic slopes in the foothill of the eastern alps palaeostresses changes correspond to distinct phases in the kinematic evolution of the northern eastern alps and to the systematic formation and reactivation of major fault zones wnw striking faults changed deformation styles from dextral shear to dextral transpression reverse faulting and finally to sinistral shear the early to middle miocene salzach ennstal fault which formed the northern boundary of the extruded central eastern alps changed from sinistral transpression to sinistral shear sinistral transtension and finally to dextral shear

thermochronological record of thrusting and strike slip faulting along the giudicarie fault system alps northern italy the giudicarie fault system represents the central approximately ne sw trending segment of the periadriatic fault system based on new fission track data the near surface evolution of the units bordering the giudicarie fault system gfs is analysed new and published zircon fission track zft data are compiled in an age contour map of the area and depict some first order features of cooling and exhumation pattern out of the three main permian plutons located in the footwall of the gfs the northern brixen pluton and southernmost kreuzberg pluton yielded zft ages of about 100 ma while the intermediate ifinger pluton cooled through the zircon partial annealing zone only in the miocene the ifinger granodiorite overthrusts the southalpine basement and the permian rocks of the athesian volcanic district along the nw dipping brittle naif fault across this thrust an important age jump from miocene to permian zft ages is observed suggesting that the deformation has jumped towards the southeast thus deactivating the related segment of the gfs the most eye catching feature of the age contour map is the corridor of young miocene zft ages from small tonalitic intrusions along the northern giudicarie fault this corridor connects early miocene 17 23 ma zft ages of the ne adamello with the middle late miocene 19 9 ma zft ages of the meran mauls basement and the western tauern window and provides evidence for a polyphase deformation along the gfs a three step evolution model is proposed for the gfs a shearing of the northern rim of the adamello batholith along the dextral strike slip periadriatic fault system b bending of the central part of the fault to a ne direction together with the adjacent intrusive rocks c dissection of the bend part meran mauls fault by the sinistral transpressive northern giudicarie fault and exhumation of small tonalitic bodies along this structure highlights different exhumation history for permian intrusions along the giudicarie fault system very consistent zft ages of 15 ma for the entire meran mauls basement corridor of miocene zircon fission track ages along the giudicarie fault system evidence for a polyphase deformation along the giudicarie fault system

contemporaneous plutonism and strike slip faulting a case study from the tonale fault zone north of the adamello pluton italian alps 1 a field microstructural and geochronological study of contemporaneous plutonism and strike slip faulting along the eastern tonale fault zone provides new insights into the interrelationships between magmatic emplacement contact metamorphism and shearing and it places new time constraints for the periadriatic fault system although pluton emplacement and shearing were not caused by each other they mutually interacted during contact metamorphism the character of the composite tonale fault zone varies considerably with its proximity to the northern margin of the adamello pluton from a paired greenschist facies mylonite belt northern mylonite zone and cataclastic fault zone in the west to a fault zone consisting of northern mylonite zone cataclastic fault zone and a second mylonite belt southern mylonite zone formed by contemporaneous shearing and contact metamorphism in the east ongoing strike slip motion led to telescoping and advective cooling of the deforming contact aureole new u pb zircon ages for the northernmost adamello intrusions the avio at 34 6 1 0 ma and the presanella at 32 0 2 3 ma date the onset of contact metamorphism rb sr and k ar cooling ages and new zircon fission track ages provide evidence that postintrusive cooling to below 300 c was achieved rapidly i e approximately 30 myr ago being consistent with a shallow crustal emplacement at ambient temperatures of approximately 250 c cataclastic dextral strike slip faulting continued until about 20 ma when the tonale fault zone became offset by a number of minor sinistral shears and by the giudicarie fault hence dextral strike slip motion along the periadriatic fault system east of the bergell pluton lasted from approximately 35 20 myr ago

exhumation in a convergent orogen the western tauern window unroofing of the western tauern window involved both low angle detachment faulting brenner fault and enhanced footwall erosion contemporaneous with upright antiformal folding this combination reflects orogen parallel e w extension during continued n s alpine convergence new fission track ages establish the relative chronology of folding and faulting and demonstrate that displacement was not always accommodated on the same surface during exhumation some units migrated from the footwall to the hanging wall of the main detachment fault due to the interplay between folding and faulting the region can effectively be divided into 3 distinct domains 1 the penninic units of the western tauern window were always in the footwall to the fault with maximum exhumation in the core of the dome due to folding and erosion 2 the lower austroalpine unit north of the tauern window was first part of the hanging wall to the brenner fault at a later stage this unit was exhumed by a further 4 5 km as part of the footwall to a more discrete through going fault the silltal fault 3 the middle and upper austroalpine units west of the tauern window were always within the hanging wall exhumation of the footwall from an initial depth of 25 km led to a transition in mechanical behaviour the curviplanar folded ductile shear zone marking the boundary to the tauern window was eventually transected by a more planar discrete brittle fault silltal fault with unit 2 now in the footwall along which the pre existing mylonites were passively exhumed to the surface

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

estimating displacement along the brenner fault and orogen parallel extension in the eastern alps the major structure accommodating orogen parallel extension in the eastern alps is inferred to be the brenner fault which forms the western boundary of the tauern window the estimated amount of extension along this fault varies from a minimum of 10 20 km to a maximum of 70 km all investigations that have attempted to constrain this amount of extension have calculated the fault plane parallel displacement required to restore the difference in structural level between footwall and hanging wall as constrained by geobarometry however these calculations neglected the component of exhumation of the footwall resulting from folding and erosion therefore the total amount of extensional displacement was systematically overestimated in the present study we project a tectonic marker surface from the footwall and hanging wall of the brenner fault onto a n s striking cross section this marker surface which is the base of the patscherkofel unit in the footwall and the base of the otztal basement in the hanging wall is inferred to have occupied the same structural level in the hanging wall and footwall of the brenner fault before its activity therefore the difference in height between the marker projected from the footwall and from the hanging wall is a measure of the vertical offset across the brenner fault this construction shows that the vertical offset of the marker horizon on both sides of the brenner fault varies strongly and continuously along strike of the brenner fault attaining a maximum value of 15 km at the hinge of the folded footwall tauern dome the along strike change of vertical offset is explained by large scale upright folding of the footwall that did not affect the hanging wall of the brenner fault therefore the difference in vertical offset of 10 km between the area of the brenner pass and the area immediately south of innsbruck corresponds to the shortening upright folding component of exhumation of the footwall the remaining 5 km of vertical offset must be attributed to extensional deformation the brenner fault itself is barely folded its dip varies between 20 and 70 and it crosscuts the upright folds of the western tauern window given the offset of 5 km the dip of the fault constrains the extensional displacement to be between 2 and 14 km we conclude that the tauern window was exhumed primarily by folding and erosion not by extensional unroofing

the lithospheric density structure of the eastern alps the three dimensional 3d lithospheric density structure of the eastern alps was investigated by integrating results from reflection seismics receiver function analyses and tomography the modelling was carried out with respect to the bouguer gravity and the geoid undulations and emphasis were laid on the investigations of the importance of deep lithospheric features although the influence of inhomogeneities at the lithosphere asthenosphere boundary on the potential field is not neglectable they are overprinted by the response of the density contrast at the crust mantle boundary and intra crustal density anomalies the uncertainties in the interpretations are in the same order of magnitude as the gravity field generated by the deep lithosphere after including the deep lithospheric geometry from the tomographic model it is shown that full isostatic equilibrium is not achieved below the eastern alps however calculation of the isostatic lithospheric thickness shows two areas of lithospheric thickening along the central axis of the eastern alps with a transition zone below the area of the transalp profile this is in agreement with the tomographic model which features a change in lithospheric subduction direction c 2005 elsevier b v all rights reserved

post collisional orogen parallel large scale extension in the eastern alps abstract large scale extension affected the eastern alps during post collisional lateral tectonic extrusion in early and middle miocene times the tauern window was mainly tectonically exhumed by the 160 km pullapart of the rigidly behaving austroalpine basement blocks forming the tectonic lid of the penninic contents of the window an evaluation of the syn extrusion fault pattern reveals displacements of several tens of kilometers along the low angle extensional shear zones at the western and eastern margins of the window and along the important strike slip fault zones north and south of the window large scale shear is reflected by discontinuities in mineral cooling patterns across important shear zones the cooling histories of the tectonic blocks show that the window boundaries during exhumation coincide only partly with the classical boundaries of the window defined by thrust units reconstruction of the exhumation history shows an asymmetric evolution of the tauern window we argue that the eastern and western low angle extensional shear zones formed in sequence which is reflected by different evolutions of the fragmentation and uplift history of the austraolpine tectonic blocks to the east and west of the window in the central and eastern alps three structural domes the lepontin dome in the central alps and the tauern and rechnitz domes in the eastern alps were formed by large scale extension in miocene times total e w stretch amounts to more than 300 km and results in 70 extension we propose that the central and eastern alps are part of an extensional province that also includes the pannonian basin and has a counterpart separated by the moesian indenter in the rhodope mountains the aegean sea and the menderes massif in asia minor in these regions a number of mainly tectonically exhumed domes or deep sedimentary basins formed by miocene large scale extension

the alpine evolution of the southern alps around the giudicarie faults a late cretaceous to early eocene transfer zone abstract data supporting relevant late cretaceous early eocene sinistral displacement along the giudicarie fault zone and a minor neogene dextral displacement along the periadriatic lineament are discussed the pre adamello structural belt is present only in the internal lombardy zone located w of the adamello massif this belt is unknown in the dolomites and surrounding areas located to the e of the giudicarie lineament upper cretaceous early eocene thick syntectonic flysch deposits of lombardy and giudicarie are well preserved along the southern and eastern border of the pre adamello belt s vergent alpine orogen towards the e in the dolomites and in the carnic alps and external dinarides only incomplete remnants of flysch deposits aptian albian and turonian maastrichtian in age are present they can be considered as equivalent to those of lombardy and giudicarie formerly in connection to each other along the n giudicarie corridor to the s the syntectonic flysch deposits are laterally replaced by the calcareous red pelagites of the scaglia rossa and by the carbonate shelf deposits of the friuli to the e and bagnolo to the s carbonate platforms the different location in the southern structural accretion of the eastern and western opposite blocks the dolomites versus the pre adamello belt can be related to the cretaceous eocene convergence in this frame the n giudicarie fault has been considered as part of a former transfer zone which produced the sinistral lateral displacement of the southern alps front for an amount of some 50 km during the late eocene to early oligocene the transfer zone was mostly sealed by the paleogene adamello batholith oligocene to neogene compressional evolution inverted the n giudicarie fault into a backthrust of the austroalpine units over the south alpine chain

from mountain summits to roots crustal structure of the eastern alps and bohemian massif along longitude 13 3 e abstract the crustal structure of the eastern alps and adjacent tectonic units investigated in this work sheds new light on the relationship of surface geology to geodynamic processes operating at depth of particular interest are the nature of a previously proposed moho gap south and east of the tauern window the plate tectonic affinity of the steeply dipping eastern alpine slab and the relationship of the alps to the neogene sedimentary basins and the bohemian massif to address these questions we use various seismological approaches based on converted waves from the temporary passive experiment easi eastern alpine seismic investigation a complementary experiment of the alparray project the easi is a densely spaced 540 km long seismic network along 13 3 e we operated for more than a year the uppermost crustal structures in and near the alps exhibit dipping layers and or tilted anisotropy that correlate well with surface geology observations the moho despite its variable appearance is clearly identified along most of the swath the variscan lithospheric blocks beneath the bohemian massif are imaged with sub vertical boundaries beneath the eastern alps the shape of the moho is consistent with bi vergent orogenic thickening with a steeper and deeper reaching adriatic plate plunging northwards beneath the european plate in the north at the junction of these plates at depth around the previously proposed moho gap the root of the eastern alps is a broad trough characterized by a zone of low velocity gradient that is up to 20 km thick transitioning between crust and mantle our receiver function results corroborate earlier lithosphere upper mantle seismic tomography images and highlight the adriatic affinity of the eastern alpine slab the zigzag deployment pattern of stations in the easi experiment also allows distinction of short wavelength variations perpendicular to the profile both within the shallow and the deep crust this underlines the importance of applying 3d imaging in complex geodynamic systems

exhumed fault bounded alpine blocks along the periadriatic lineament the eder unit carnic alps austria the eder unit in the carnic alps which is situated immediately south of the periadriatic lineament pl represents a fault bounded block consisting of a low grade up to 400 c indicated by epizonal illite crystallinity values recrystallized quartz and non recrystallized white mica metamorphic paleozoic metasedimentary sequence until now it has been assumed to represent a separate variscan nappe the rocks of the eder unit show a strong e to w oriented stretching lineation on steep foliation planes d1 subparallel to the pl d1 structures originated near the temperature peak of metamorphism and shear sense indicators show dextral ductile shear parallel to the pl tight mesoscale d2 folds formed on the cooling path k ar and ar ar ages from newly formed white mica cluster around 32 28 and 18 13 ma and suggest a two stage tertiary history of the eder unit we interpret the eder unit as a fault bounded block formed during oligocene large scale dextral shearing along the pl near tmax and exhumed in mid miocene times during another phase of activity along the pl its nature as a separate variscan nappe is questioned

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

strike slip movements and thrusting along a transpressive fault zone the north giudicarie line insubric line northern italy this paper analyzes the kinematic evolution and the deformation partitioning within an important transpressive fault zone located in the central part of the alpine chain the north giudicarie line is a nne trending fault which offsets the dextral insubric line with an apparent left lateral displacement of about 70 km the main fault plane of the north giudicarie line dips about 35 45 to the nw the footwall is characterized by n s striking strike slip faults which reactivate extensional faults of early jurassic to late cretaceous age the early deformation history of the north giudicarie line is revealed by basement and limestone mylonites shear sense of mylonites indicates on average top to the east thrusting these movements took place during the late oligocene early miocene when the insubric line was active as a right lateral strike slip fault therefore in this time span the north giudicarie line can be interpreted as a dextral transpressive bend of the insubric line mylonites have later been overprinted by brittle faults related to top to the se thrusting of middle late miocene age during this event the shape of the insubric line was strongly modified by left lateral transpression along the giudicarie fault zone deformation was partitioned between prevailing compression along the giudicarie line and left lateral strike slip movements along the n s striking faults these faults transferred the strike slip component of the giudicarie line into a wider area of the central southern alps

reconstructing the alps carpathians dinarides as a key to understanding switches in subduction polarity slab gaps and surface motion palinspastic map reconstructions and plate motion studies reveal that switches in subduction polarity and the opening of slab gaps beneath the alps and dinarides were triggered by slab tearing and involved widespread intracrustal and crust mantle decoupling during adria europe collision in particular the switch from south directed european subduction to north directed wrong way adriatic subduction beneath the eastern alps was preconditioned by two slab tearing events that were continuous in cenozoic time 1 late eocene to early oligocene rupturing of the oppositely dipping european and adriatic slabs these ruptures nucleated along a trench trench transfer fault connecting the alps and dinarides 2 oligocene to miocene steepening and tearing of the remaining european slab under the eastern alps and western carpathians while subduction of european lithosphere continued beneath the western and central alps following the first event post late eocene nw motion of the adriatic plate with respect to europe opened a gap along the alps dinarides transfer fault which was filled with upwelling asthenosphere the resulting thermal erosion of the lithosphere led to the present slab gap beneath the northern dinarides this upwelling also weakened the upper plate of the easternmost part of the alpine orogen and induced widespread crust mantle decoupling thus facilitating pannonian extension and roll back subduction of the carpathian oceanic embayment the second slab tearing event triggered uplift and peneplainization in the eastern alps while opening a second slab gap still present between the eastern and central alps that was partly filled by northward counterclockwise subduction of previously unsubducted adriatic continental lithosphere in miocene time adriatic subduction thus jumped westward from the dinarides into the heart of the alpine orogen where northward indentation and wedging of adriatic crust led to rapid exhumation and orogen parallel escape of decoupled eastern alpine crust toward the pannonian basin the plate reconstructions presented here suggest that miocene subduction and indentation of adriatic lithosphere in the eastern alps were driven primarily by the northward push of the african plate and possibly enhanced by neutral buoyancy of the slab itself which included dense lower crust of the adriatic continental margin

coeval high pressure metamorphism thrusting strike slip and extensional shearing in the tauern window eastern alps 1 recent findings for a young 31 5 0 7 ma age of high pressure metamorphism at 90 km depths in the eclogite zone of the tauern window eastern alps prompt the question about the timing of the structural development of the tauern window and its relation to high pressure metamorphism we show that all major structures in the tauern window resulting from strong n s lithospheric shortening and simultaneous minor e w extension began developing coevally with high pressure metamorphism in the eclogite zone large scale strike slip shear zones started to form at 32 30 ma and facilitated the spatial accommodation of simultaneous shortening and extension at least some of the strike slip and extensional shear zones operated into the middle miocene either continuously or intermittently with pronounced activity at 21 15 ma the considerable exhumation of the eclogite zone from 90 km depths into the middle crust and the tectonic development of its framework occurred within only 1 2 ma after eclogitization this is evidenced by almost identical ages for eclogite facies metamorphism and for the development of the major structures that bound the eclogite zone under blueschist and greenschist facies metamorphic conditions we discuss a tectonic model in which considerable transpressional shortening and thickening took place in the present central southern part of the tauern window we propose that the tauern window nucleated here and that most of the regional deformation at 32 30 ma is today found at the periphery of the window and in the adjacent austroalpine units afterward transpression continued the window grew to the e w and n and deformation progressed to those parts of the window ductile deformation in the present day surface level ceased at 15 ma

lateral extrusion in the eastern alps revisited refining the model by thermochronological sedimentary and seismic data 1 this study comprises a reassessment of the classical model of lateral extrusion in the eastern alps by using recently published geochronological data sedimentary ages from intramontane basins ages and distribution of magmatic rocks and information from seismic profiles extrusion related faulting continuously propagated from the western toward the central eastern part of the eastern alps during oligocene to middle miocene times this is confined by oblique convergence between the adriatic and european plates during middle miocene times extrusion became not only lateral in terms of parallel to the trend of the eastern alps but was characterized by a displacement vector at a high angle to the strike of the orogen this resulted in the exhumation of the schladming and pohorje blocks that were exhumed within extensional bridges at the northern and southern terminations of the pols lavanttal fault system respectively from middle miocene to recent times extrusion was controlled by overall extension between the dinaric and carpathian subduction zones the influence of north directed compression triggered by the northward moving adriatic plate diminished and the influence of the retreating carpathian subduction zone increased this gave rise to miocene volcanism that is exclusively found east of the dinaric subduction zone we therefore consider that lateral extrusion in the eastern alps can be subdivided into distinct tectonic phases with less pronounced eastward extension related displacement between late oligocene and middle miocene times as soon as the eastern alps passed the dinaric subduction zone the entire domain became highly extensive

modes of orogen parallel stretching and extensional exhumation in response to microplate indentation and roll back subduction tauern window eastern alps the tauern window exposes a paleogene nappe stack consisting of highly metamorphosed oceanic alpine tethys and continental distal european margin thrust sheets in the eastern part of this window this nappe stack eastern tauern subdome etd is bounded by a neogene system of shear the katschberg shear zone system kszs that accommodated orogen parallel stretching orogen normal shortening and exhumation with respect to the structurally overlying austroalpine units adriatic margin the kszs comprises a 5 km thick belt of retrograde mylonite the central segment of which is a southeast dipping low angle extensional shear zone with a brittle overprint katschberg normal fault knf at the northern and southern ends of this central segment the kszs loses its brittle overprint and swings around both corners of the etd to become subvertical dextral and sinistral strike slip faults the latter represent stretching faults whose displacements decrease westward to near zero the kinematic continuity of top east to top southeast ductile shearing along the central low angle extensional part of the kszs with strike slip shearing along its steep ends combined with maximum tectonic omission of nappes of the etd in the footwall of the knf indicates that north south shortening orogen parallel stretching and normal faulting were coeval stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the kszs to have begun at 23 21 ma leading to rapid cooling between 21 and 16 ma this exhumation involved a combination of tectonic unroofing by extensional shearing upright folding and erosional denudation the contribution of tectonic unroofing is greatest along the central segment of the kszs and decreases westward to the central part of the tauern window the kszs formed in response to the indentation of wedge shaped blocks of semi rigid austroalpine basement located in front of the south alpine indenter that was part of the adriatic microplate northward motion of this indenter along the sinistral giudicarie belt offsets the periadriatic fault and triggered rapid exhumation of orogenic crust within the entire tauern window exhumation involved strike slip and normal faulting that accommodated about 100 km of orogen parallel extension and was contemporaneous with about 30 km of orogen perpendicular north south shortening of the etd extension of the pannonian basin related to roll back subduction in the carpathians began at 20 ma but did not affect the eastern alps before about 17 ma the effect of this extension was to reduce the lateral resistance to eastward crustal flow away from the zone of greatest thickening in the tauern window area therefore we propose that roll back subduction temporarily enhanced rather than triggered exhumation and orogen parallel motion in the eastern alps lateral extrusion and orogen parallel extension in the eastern alps have continued from 12 to 10 ma to the present and are driven by northward push of adria

40ar 39ar muscovite ages from the penninic austroalpine plate boundary eastern alps the radstadt mountains eastern alps expose the tectonic boundary between the base of the austroalpine continental plate hanging wall and the penninic oceanic units foot wall parts of the austroalpine basement were penetratively deformed because of ongoing rifting of the continental crust during the permian 290 250 ma austroalpine permo mesozoic cover rocks were deformed during the cretaceous 80 ma and the paleogene 55 50 ma these ages are interpreted as representing two distinct events of nappe stacking the younger ages represent the collision of austroalpine and penninic tectonic units the penninic nappe complex displays a successive decrease of ages from 37 to 25 ma from high to deep tectonic levels a second age group of 22 ma was found both in low temperature release steps and as plateau ages close to the penninic austroalpine boundary it is attributed to a thermal overprint due to ductile extension of the overthickened orogenic wedge

late oligocene neogene evolution of europe adria collision new structural and geochronological evidence from the giudicarie fault system italian eastern alps the giudicarie fault system giudicarie sensu stricto meran mauls passeier thurnstein and jaufen faults represents a sharp break in the generally e w strike direction of the orogen scale periadriatic fault system and is a key element for understanding the late oligocene neogene evolution of the alpine chain the kinematics timing and magnitude of movements on the giudicarie fault system are presented here on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples two main tectonic phases are established 1 back thrusting of the austroalpine units over the southern alps around 32 ma recorded by basement and limestone mylonites along the giudicarie and meran mauls faults with transport directions toward 100 110 and 2 later sinistral transpressive displacement characterized by structures at the ductile brittle transition which overprinted the top to e ese thrust related mylonites but also partitioned into a major system of transcurrent faults in the southalpine domain it was during this later event that the periadriatic fault attained its present day geometry however the amount of sinistral displacement along the giudicarie system was only 15 20 km the magnitude is established here from the 15 km sinistral offset of the jaufen mylonites across the passeier brittle fault and the 20 km long gap in the otherwise continuous distribution of oligocene tonalitic lamellae along the giudicarie fault a direct structural connection is also established between the brenner and the jaufen faults this constrains the timing of the second phase since it must postdate the main exhumation phase of the tauern window at 20 18 ma the results of this study argue against an originally straight periadriatic fault the giudicarie fault formed a restraining bend in this part of the periadriatic fault system since at least the late miocene and probably since the late oligocene

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

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

geochronological constraints on the evolution of the periadriatic fault system alps fault rocks from various segments of the periadriatic fault system paf alps have been directly dated using texturally controlled rb sr microsampling dating applied to mylonites and both stepwise heating and laser ablation 40ar 39ar dating applied to pseudotachylytes the new fault ages place better constraints on tectonic models proposed for the paf particularly in its central sector along the north giudicarie fault oligocene e se directed thrusting 29 32 ma is currently best explained as accommodation across a cogenetic restraining bend within the oligocene dextral tonale pustertal fault system in this case the limited jump in metamorphic grade observed across the north giudicarie fault restricts the dextral displacement along the kinematically linked tonale fault to 30 km dextral displacement between the tonale and pustertal faults cannot be transferred via the peio fault because of both late cretaceous fault ages 74 67 ma and sinistral transtensive fault kinematics in combination with other pseudotachylyte ages 62 58 ma widespread late cretaceous paleocene extension is established within the austroalpine unit coeval with sedimentation of gosau group sediments early miocene pseudotachylyte ages 22 16 ma from the tonale pustertal jaufen and passeier faults argue for a period of enhanced fault activity contemporaneous with lateral extrusion of the eastern alps this event coincides with exhumation of the penninic units and contemporaneous sedimentation within fault bound basins

eclogite meso and microfabrics implications for the burial and exhumation history of eclogites in the tauern window eastern alps from p t d paths abstract the eclogite zone of the central southern tauern window comprises eclogites and associated high pressure metasediments that are intercalated between penninic basement units in the foot wall and an imbricate stack in the hanging wall this nappe stack consists of continental basement units cover sequences of a distal continental slope and the main part of the ophiolitic glockner nappe textures and microfabrics of eclogites from the central southern tauern window allow the establishment of the eclogitic and post eclogitic deformation histories from burial by subduction to subsequent exhumation the metamorphic evolution of the eclogites is documented by 1 initial greenschist to blueschist facies 2 eclogite facies at ca 550 630 c and 20 kbar 3 a second blueschist facies overprint ca 450 c 10 15 kbar and 4 exhumation to pressures of ca 6 7 kbar at 500 550 c upper greenschist to lower amphibolite facies an eclogitic penetrative foliation s 1 and s dipping stretching lineation l 1 formed during the final stages of subduction of the eclogite bearing unit the p t evolution of the eclogites during d 1 documents the final increment of the prograde p t path later blueschist facies metamorphism is contemporaneous to top to the n emplacement of the eclogite bearing unit onto continental basement units within a subduction zone we discuss two models of eclogite emplacement most probably emplacement is achieved by a thrust along the base of the eclogite bearing unit alternatively the p t path of the eclogite facies rocks suggests an emplacement model similar to corner flow subsequent to eclogite and nappe emplacement the nappe stack is entirely affected by a penetrative deformation d 2 that resulted in the development of a mylonitic foliation s 2 and an e w oriented stretching lineation l 2 within lower amphibolite to upper greenschist facies this deformation is related to a crustal scale detachment zone that formed during the exhumation of the penninic units

peak temperature patterns of polyphase metamorphism resulting from accretion subduction and collision eastern tauern window european alps a study with raman microspectroscopy on carbonaceous material rscm raman microspectroscopy on carbonaceous material rscm from the eastern tauern window indicates contrasting peak temperature patterns in three different fabric domains each of which underwent a poly metamorphic orogenic evolution domain 1 in the northeastern tauern window preserves oceanic units glockner nappe system matrei zone that attained peak temperatures tp of 350 480 c following late cretaceous to palaeogene nappe stacking in an accretionary wedge domain 2 in the central tauern window experienced tp of 500 535 c that was attained either within an exhumed palaeogene subduction channel or during oligocene barrovian type thermal overprinting within the alpine collisional orogen domain 3 in the eastern tauern subdome has a peaktemperature pattern that resulted from eo oligocene nappe stacking of continental units derived from the distal european margin this pattern acquired its presently concentric pattern in miocene time due to post nappe doming and extensional shearing along the katschberg shear zone system kszs tp values in the largest hochalm dome range from 612 c in its core to 440 c at its rim the maximum peak temperature gradient 70 c km 1 occurs along the eastern margin of this dome where mylonitic shearing of the katschberg normal fault knf significantly thinned the subpenninic and penninic nappe pile including the pre existing peak temperature gradient

dating the longevity of ductile shear zones insight from 40ar 39ar in situ analyses we attempt to improve temporal constraints on the longevity and the termination of ductile shear zones by performing texturally controlled in situ 40ar 39ar analyses of pre kinematic muscovite biotite and k feldspars of syn kinematic phengite and k feldspar and of post kinematic phengite within the same samples of sinistral shear zones from the western tauern window eastern alps additionally two samples were dated by the rb sr method microsampling relative sequences of mineral formation based on microstructural cross cutting relationships were confirmed by in situ 40ar 39ar analyses showing that syn kinematic minerals are in general younger than pre kinematic minerals and older or of equal age than the post kinematic minerals of the same sample from the rim to the core of the western tauern window syn kinematic phengite and k feldspar reveal a set of formation ages varying between 33 and 15 ma for the northernmost and peripheral shear zone ahorn shear zone between 24 and 12 ma for the intermediate shear zone network tuxer shear zones and between 20 and 7 ma for the southernmost and central shear zone greiner shear zone the age variation of syn kinematic phengite and k feldspar analyses is larger than the analytical error of each age obtained in addition isochron calculations of the syn kinematic minerals reveal atmospheric like 40ar 36ar intercepts therefore the obtained age values of the syn kinematic minerals are interpreted as formation ages which date increments of a long lasting deformation period the time range of deformation of each shear zone system is bracketed by the oldest and youngest formation ages of syn kinematic phengite and k feldspar post kinematic phengite laths show the youngest formation ages and overlap with the youngest syn kinematic formation ages this relationship indicates that post kinematic growth occurred immediately after syn kinematic mineral formation at the end of ductile sinistral shear hence the termination of deformation is dated by the ages of these post kinematic phengite blasts pre kinematic minerals are characterized by break down and exsolution reactions and their age values are heterogeneous and often affected by the presence of extraneous ar these age values are usually older than but sometimes overlapping with ages of the syn kinematic minerals using the temporal constraints obtained by the ages of pre syn and post kinematic minerals we could assess partly overlapping time intervals of syn kinematic mineral formation of 19 myr 33 15 ma in the ahorn shear zone 13 myr 24 12 ma in the tuxer shear zones and 14 myr 20 7 ma in the greiner shear zone this indicates successive localization and propagation of ductile shear zones in the western tauern window from lower metamorphic sites at the rim towards higher metamorphic sites in the center

progressive strain localization in a major strike slip fault exhumed from midseismogenic depths structural observations from the salzach ennstal mariazell puchberg fault system austria 1 analysis of a strike slip fault exhumed from midseismogenic depths reveals that the fault experienced progressive strain localization toward a high strain fault core we focus on the ennstal segment of the 400 km long salzach ennstal mariazell puchberg semp strike slip fault system in the eastern alps which accommodated 60 km of left lateral displacement during oligo miocene time macroscopic and microscopic observations reveal a zoned fault featuring a high strain core at least 10 m wide within a fault zone that is at least 150 m wide grain size distribution analysis shows how the ennstal segment of the semp evolved our data reveal a 10 m wide high strain fault core characterized by a power law relationship of grain sizes d2 2 0 bordered by a 54 m wide transition zone where the largest and smallest grains are characterized by two power law relationships d2 2 0 and 1 6 respectively this zone is in turn bordered by a region with grain sizes that show a single low strain power law relationship of d2 1 6 we interpret these relationships to be the result of concentrated shear overprinting an initial low strain power law grain size distribution before strain localized to the core this is consistent with the theory that faults mature by smoothing geometrical complexities forming a highly localized high strain fault core the data do not support the idea that damage forms primarily in response to dynamic stresses during seismic rupture although they do suggest that this mechanism may operate within tens of meters of the fault once it has developed its zoned structure

on the causes and modes of exhumation and lateral growth of the alps 1 a compilation of the apatite and zircon fission track ages of the alpine chain points to markedly different patterns of cooling and exhumation of the eastern alps compared to the central and western alps the site of exhumation and shortening in the western alps migrated outward whereas it was more stationary in the eastern alps where it created a narrower metamorphic belt a correlation of these observations to the deep structure of the orogen suggests that north directed lower crustal wedging induces northward propagation of the deformation and exhumation front in the middle and upper crust of the central and western alps the absence of such lower crustal wedges in the eastern alps does not induce a similar shift of deformation but rather a long term localization of shortening and exhumation in one and the same area namely the axial zone of the orogen a critical review of the temporal correlations between inferred changes in the erosional efficiency of the alps and tectonic phases points to a negative correlation and hence no erosional control on the shifts of the deformation front of the alps therefore we conclude that changes in the deep structure and rheology of the orogen instead of changes in its erosional efficiency exerted the prime control on the lateral growth of the alps

comment on rosenberg and garcia estimating displacement along the brenner fault and orogen parallel extension in the eastern alps int j earth sci geol rundsch 2011 100 1129 1145 the western end of the tauern window is marked by what we refer to as the brenner normal fault zone the brenner fault since the late eighties is known as a textbook example of a normal fault already in 1934 dunner proposed west directed normal faulting related to updoming of the footwall i e the tauern window these earlier publications e g schmidegg 1953 mainly focussed on a brittle normal fault known as silltal fault that represents a northern segment of the brenner normal fault zone behrmann 1988 and selverstone 1988 were the first to also describe ductile components of normal faulting in an area further south referred to as sterzing steinach mylonite zone behrmann or brenner line selverstone in 1997 fugenschuh et al presented a two stage model for the evolution of the brenner normal fault zone thereby ductile normal faulting was restricted to an area between sterzing and matrei during stage 1 referred to as brenner normal fault s str in this contribution while brittle faulting during stage 2 not only overprinted the earlier mylonites of the brenner line s str but extended further north into the entirely brittle silltal fault this model involved coeval n s compression and e w extension during stage 1 the published calculated total amounts of related e w extension derived from metamorphic data and distinct exhumation histories in footwall and hanging wall and from the estimated dip of the overall fault zone varied significantly between 10 and 20 km e g behrmann 1988 and up to 70 km e g fugenschuh et al 1997 the contribution of exhumation by erosion as a consequence of coeval n s compression has never been explicitly considered and calculated so far

frictional viscous flow in mylonite with varied bimineralic composition and its effect on lithospheric strength abstract a theoretical composite flow law is presented for mylonite containing interconnected layers of a weak mineral undergoing power law creep and porphyroclasts of a stronger mineral undergoing fracture and frictional sliding such mylonite termed clastomylonite is said to undergo frictional viscous fv mylonitic flow its bulk strength is expressed as a function of bimineralic composition temperature effective pressure and shear strain rate as well as the material parameters for the constituent minerals the fv flow law predicts that the rheology of clastomylonite is predominantly non linear viscous and only slightly pressure sensitive for most bimineralic compositions fv mylonitic flow is shown to occupy a depth interval between cataclastic flow involving adhesive wear in the upper crust and fully viscous mylonitic flow at greater depths the transition from adhesive wear to fv mylonitic flow is related to the onset of dislocation creep glide plus climb in the weakest phase and is inferred to coincide with a crustal strength maximum a peak strength of about 80 mpa is calculated with a combination of byerlee s constants for frictional sliding of granite and the fv flow law for granitic clastomylonite 30 vol quartz at elevated fluid pressures this value falls within the range of flow stresses independently obtained from quartz palaeopiezometry in many greenschist facies granitic mylonite zones

paleomagnetic rotation constraints on the deformation of the northern qaidam marginal thrust belt and implications for strike slip faulting along the altyn tagh fault discordant cenozoic paleomagnetic rotation results obtained throughout the northeastern tibetan plateau have yielded different tectonic models for the evolution of the altyn tagh fault and the northeastern tibetan plateau here based on detailed existing magnetostratigraphic age constraints we carried out an in depth paleomagnetic study along the hongliugou section in the middle northern qaidam marginal thrust belt to address the cenozoic rotations of this region a total of 1 342 jurassic neogene siltstone sandstone core samples were collected from 128 sites across 18 time intervals rock magnetic analysis suggested that magnetite and hematite are the dominant magnetic carriers detailed thermal demagnetization analyses were performed and the characteristic remanent magnetizations of 90 sites 743 samples were obtained which yielded positive fold and reversals tests indicating that they likely represent primary magnetizations detailed paleomagnetic declination versus age analyses revealed three periods of rotations 12 515 7 degrees statistically insignificant counterclockwise rotations during 45 33ma successive clockwise rotations of 32 215 4 degrees during 33 14ma and subsequent statistically insignificant counterclockwise rotations of 8 79 4 degrees after 14ma these three periods of rotations are similar to those calculated based on previously available magnetostratigraphic data from the nearby dahonggou section based on the integration of these data with other lines of geological evidence we attributed the latter two periods of rotations to fast strike slip faulting along the altyn tagh fault

quantifying tectonic versus erosive denudation by the sediment budget the miocene core complexes of the alps abstract the denudation budget of the alps is quantified for the main period of lateral extrusion between 22 and 12 ma the relative importance of tectonic denudation increases from w to e from 70 in the lepontine window in the swiss alps to 80 in the tauern window and to more than 95 in the rechnitz window the driving mechanism of tectonic denudation was eastward extrusion due to an unconstrained orogenic margin in the pannonian basin tectonic denudation in the alps was responsible for about 30 of the total exhumation between 22 and 12 ma

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

prograde retrograde p t t deformation path of austroalpine micaschists during variscan continental collision eastern alps a complete prograde p t path defined by 10 calculated p t fields in succession is recognized from metapelites by using geothermobarometry on garnet bearing assemblages with microstructural control overstacking of several tectonic units during an early variscan continental collision explains the complex prograde p t history isostatic uplift and deformation controlled the retrograde p t path deformation with changing character acted continuously during all stages of the evolution of the austroalpine basement complex after the intrusion of caledonian granitoids metapelites and magmatic rocks suffered a shearing deformation d1 d2 which produced sheath folds as well as the main foliation s2 spessartine rich first generation garnets situated in microlithons enclosed by s2 record the onset of shearing under increasing high pressure low temperature conditions 7 kbar 380 c geothermobarometry on second generation garnets which have been rotated during growth indicates isothermal decompression from 9 kbar to 5 kbar 500 c and subsequent recompression heating during continuing shearing this is explained by overthrusting of a tectonic unit unit 2 from ne to sw upon the micaschist unit unit 1 followed by isostatic uplift and further overstocking of a third unit unit 3 the resulting pmax of 12 kbar at 650 c and further increasing temperatures up to 680 c accompanied by decompression have been calculated using a third generation of garnets these high pressure high temperature conditions may explain the occurrence of eclogitic metabasites in adjacent regions staurolite and kyanite first appeared under decreasing pressures at the last stage of prograde p t evolution shortening deformation d3 and simultaneous growth of typical amphibolite facies minerals staurolite 2 kyanite 2 sillimanite andalusite occurred during the retrograde path a final step of variscan evolution was marked by an oppositely directed shearing d4 at t 300 c and p 3 kbar possibly indicating backthrusting or extension apart from acid intrusions no signs of a previous caledonian thermotectonic history were found in the area to the south of the defereggen antholz vals line

shortening budgets and the role of continental subduction during the india asia collision abstract the india asia collision provides a remarkable example of diffused deformation because the zone of compressive strain extends far into the hinterland of the himalaya molnar and tapponnier s science 189 1975 419 concept of india as a rigid indenter responsible for the diffused deformation has been widely accepted perhaps uncritically this review gives a reappraisal of landmark papers by dewey et al philos trans r soc london a 327 1988 379 eclogae geol helv 82 1989 717 which discussed the shortening budget in se asia and the evidence for the amount and the rate of the convergence between india and asia taking place after the initial collision of these continents at roughly 55 50 ma evidence for the total convergence comes from magnetic anomaly palaeomagnetic and volumetric balancing studies the results are consistent in showing about 1800 2100 km convergence between india and asia in the western sector 2475 km in the central and 2750 2800 km in the eastern sector the rate of convergence between india and asia over the period since initial collision is roughly 5 cm year however the possible long term rate of convergence within the himalaya is considerably less i e 1 5 2 0 cm year a fraction of the total convergence this shortfall can be made up by adding to the rate for the himalaya alone the convergence rates in other parts of the diffused zone of compressive strain i e tibet tien shan altai this works well for the post oligocene but not for the earlier post collisional history when the areal extent of thrust fold tectonics was much more limited possibly the apparent shortening deficit before the miocene was made up by strike slip faulting but with the notable exception of the red river fault evidence for widespread pre miocene strike slip faults is not convincing summation of the amount of shortening in thrust fold regimes in the himalaya and its hinterland falls short of that required by the total convergence figures quoted above the deficit arises firstly because of the likelihood that pre collisional crustal shortening of uncertain areal extent in tibet reduces tibet s contribution 40 according to dewey et al philos trans r soc london a 327 1988 379 eclogae geol helv 82 1989 717 to the shortening budget for the cenezoic revised shortening budgets are presented on the assumption that most of the lhasa block southern tibet was already thickened prior to collision this thickening is difficult to quantify secondly balanced cross sections from various parts of the himalaya give 60 70 shortening that is only about 500 km roughly half of the shortening proposed by dewey et al the conclusion of le pichon et al tectonics 11 1992 1085 that only indian mid upper crust is involved in the himalayan thrust sheets is supported but it needs to be reassessed in the light of the recognition of eocene oligocene thickening in the himalaya this early crustal thickening antedates the sequence of thrusts which started with the main central thrust and therefore the shortening estimates based on balanced cross sections probably underestimate the total shortening in the himalaya the prospect of substantial underthrusting of india beneath tibet minimizes the amount of horizontal shortening of tibetan lithosphere during the cenozoic the conclusion is that either the total convergence deduced from geophysical and volumetric work is too large or the deficit must be made up by shortening mechanisms other than thrust fold regimes i e strike slip faulting which serves to move rocks out of the way of india

thrust regime and transpression regime tectonics in the tauern window eastern alps below the penninic nappes of the tauern window the deepest level of the alpine thrust system is exposed in the parautochthonous sedimentary sequence of helvetic facies

rb sr microchrons of synkinematic mica in mylonites an example from the dav fault of the eastern alps abstract a technique for texturally controlled microsampling from rock thick sections and subsequent rb sr dating of g sized samples has been developed it allows direct dating of minerals unequivocally related to deformation the technique has been applied to strictly synkinematically grown white mica prepared from mylonites related to the defereggen antholz vals dav fault south of the tauern window eastern alps control of deformation ages is provided by field relationships with independently dated plutons and dykes dated here by single mineral rb sr the field observations and isotopic ages are fully consistent and demonstrate that this is a reliable method for sub mm scale geochronology the ages obtained establish that sinistral strike slip shearing associated with the dav fault lasted from at least 33 ma to 30 ma followed by an abrupt change to dextral transpression related to the adjacent periadriatic fault

deformation partitioning during updoming of the sonnblick area in the tauern window eastern alps austria the sonnblick dome forms a ne vergent dome structure cored by basement gneisses within the southeastern tauern window of the eastern alps austria a succession of ductile and brittle deformation stages documents doming and exhumation subsequent to the thermal peak of metamorphism contrasting deformation geometries within internal parts and along the margins of the dome are explained in terms of deformation partitioning subhorizontal shortening is documented by subvertical en echelon extensional gashes within central parts of the dome subhorizontal as well as subvertical flattening is also documented by fold structures during dextral transpression strike slip is accommodated along the ne margin sonnblick lamella moll valley fault and the southern margin moser fault of the sonnblick dome while vertical thickening occurred within the interior of the dome crustal thickening triggered unroofing and extension parallel to the dome axis which is documented by ductile low angle normal faults in the uppermost structural sections of the dome this normal fault system contributed to footwall uplift and exhumation of the dome structure the sonnblick lamella associated with the dextral moll valley fault forms a stretching fault where deformation is concentrated along a potential zone of weakness this fault is interpreted to represent the transition from vertical thickening within the dome to vertical thinning at the dome margins during upbending the dome structure passed the isotropic stress surface that is characterized by equality of 1 and 2 this is documented in a perturbation of the orientations of principal stress axes 1 and 2 while 3 remains constant in orientation transpression contributed substantially to updoming and to rapid nearly isothermal exhumation subsequent to the thermal peak of metamorphism

young alpine dykes south of the tauern window austria a k ar and sr isotope study fortyfive new k ar ages and sr isotope data on amphiboles biotites clinopyroxenes and whole rock samples from subvolcanic dykes south of the tauern window establish that alkalibasaltic dykes were intruded 30 m y ago and shoshonitic volcanism occured between 30 and 24 m y ago two calc alkaline rocks of high potassium composition yielded ages of 40 and 26 m y resp a spread which may or may not be real calc alkaline dykes with medium and low potassium contain excess argon and are hence undatable alkalibasaltic dykes have 87sr 86sr ratios of 0 7056 0 7070 shoshonitic rocks 0 7075 0 7133 potassium rich calc alkaline dykes 0 7077 0 7100 87sr 86sr of all other calc alkaline rocks scatter between 0 7074 and 0 7150 sr data indicate that dykes studied do not represent closed sr systems but that sr characteristics result from selective strontium assimilation en route to surface primary sr isotopic ratios of alkalibasaltic dykes point to an origin of these rocks in enriched sub continental upper mantle the source region of shoshonitic and high potassium calcalkaline rocks could have 87sr 86sr around 0 707 which is assigned to the input of a component rich in alkalies lree and lil elements genetic relationships with other tertiary magmatites of similar geotectonic position are explained in terms of plate tectonic models of the eastern alps

alpine metamorphism in the south east tauern window austria 1 p t variations in space and time the pennine rocks exposed in the south east tauern window austria contain mineral assemblages which crystallized in the mid tertiary late alpine regional metamorphism the pressure and temperature conditions at the thermal peak of this event have been estimated for rocks at four different structural levels using a variety of published and thermochemically derived geobarometers and geothermometers the results are a in the garnet chlorite zone 2 5 km structurally above the staurolite biotite isograd t 490 50 c p 7 1 kbar b within 0 5 km of the staurolite biotite isograd t 560 300c p 7 1 kbar c in the staurolite biotite zone c 2 5 km structurally below the staurolite biotite isograd t 610 30 c p 7 6 1 2 kbar d in the staurolite biotite zone 3 4 km structurally below the staurolite biotite isograd t 630 40 c p 6 6 1 2 kbar the pressure estimates imply that the total thickness of overburden above the basement cover interface in the mid tertiary was c 26 4 km this overburden can only be accounted for by the austro alpine units currently exposed in the vicinity of the tauern window if the altkristallin the middle austro alpine nappe was itself buried beneath an upper austro alpine nappe or nappe pile which was 7 4 km thick at that time the occurrence of epidote margarite quartz pseudomorphs after lawsonite in garnet indicates that part of the mesozoic pennine cover sequence in the south east tauern experienced blueschist facies conditions t 450 c p 12 kbar in early alpine times evidence from the central tauern is used to argue that the blueschist facies imprint post dated the main phase of tectonic thickening d1a and was thus a direct consequence of continental collision combined oxygen isotope and fluid inclusion studies on late stage veins thought to have been at lithostatic pressure and in thermal equilibrium with their host rocks during formation suggest that they crystallized from aqueous fluids at 1 1 0 4 kbar and 420 20 c early alpine late alpine and vein formation p t constraints have been used to construct a p t path for the base of the mesozoic cover sequence in the south east tauern window the prograde part of the p t path between early and late alpine metamorphic imprints is unlikely to have been a smooth curve and may well have had a low dp dt overall the decompression presumably due to erosion which occurred immediately before the thermal peak and possibly also earlier in the tertiary was probably partly or completely cancelled by the effects of early to mid tertiary d2a tectonic thickening the thermal peak of metamorphism was followed by a phase of almost isothermal decompression which implies a period of rapid uplift in the middle tertiary the peak metamorphic p t estimates are compared with the solutions of england s 1978 one dimensional conductive thermal model of the eastern alps and are shown to be consistent with the idea that the late alpine metamorphism was caused by tectonic burial of the pennine zone beneath the austro alpine nappes in the absence of extraneous heat sources such as large intrusions at depth

fracture driven intrusion and upwelling of a mid crustal pluton fed from a transpressive shear zone the rieserferner pluton eastern alps the rieserferner pluton was emplaced at a depth of 12 15 km into steeply dipping greenschist facies mylonitic rocks of the austroalpine basement just south of the tauern window eastern alps intrusion occurred during north south directed shortening and east west horizontal extension in front of the rigid southern alpine indenter the regional strain field is transpressive with a strong coaxial component and is characterized by east west stretching tonalitic melt ascended through a feeder channel preserved in the steep southern part of the rieserferner pluton within and adjacent to the steep mylonitic foliation of a major shear zone the defereggen antholz vals dav line melt ascent was perpendicular to the north south shortening direction in the country rocks magma emplacement involved melt induced hydro fracturing to form a subhorizontal tabular pluton that protruded northward from the dav line into the previously folded country rocks during the late stage of emplacement buoyant upwelling of the partly recrystallized magma induced doming of the pluton roof as well as vertical ductile shortening of the directly overlying country rocks magma pressure therefore locally exceeded the lithostatic pressure thermal modeling constrains the maximum time for doming and solidification of the pluton to have been 32 000 yr the wavelength of the domes in the pluton roof indicates the viscosity contrast between country rock and partly crystallized tonalite in the pluton to have been at least 100 1

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

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

geothermobarometry in metasediments of the southern grossvenediger area tauern window austria metasediments in the southern grossvenediger area tauern window austria were studied along a cross section through rocks of increasing metamorphic grade from the margin of the tauern window in the south to the base of the upper schieferhulle including the eclogite zone in the north in the southern part of the cross section there is no evidence for a pre late alpine metamorphic history in the form of high pressure relics or pseudomorphs mineral assemblages are characterized by the stability of tremolite calcite biotite calcite and biotite chlorite calcite in the northern part a more complete alpine metamorphic evolution is preserved primary high pressure assemblages are dolomite quartz tremolite zoisite zoisite dolomite quartz phengite i and probably tremolite dolomite phengite i secondary post kinematic assemblages tremolite calcite talc calcite phengite ii chlorite calcite quartz biotite chlorite calcite biotite zoisite calcite formed as a result of the dominant late alpine metamorphic overprint the occurrence of biotite zoisite calcite is confined to the northernmost area and defines a biotite zoisite calcite isograd p t estimates based on standard thermobarometric techniques and on stability relationships of tremolite calcite dolomite quartz and zoisite give consistent results p t conditions of the main tertiary metamorphic overprint were 525 c p 7 5 1 kbar in the northern part of the cross section the southern part was metamorphosed at lower temperatures of 430 470 c the si content of phengites from this area is almost as high as that of phengites from the eclogite zone simax 3 4 pfu pressures 10 kbar at 420 c are suggested by phengite barometry according to massone schreyer 1987 in the absence of high pressure relics or pseudomorphs these phengites which lack late alpine re equilibration are the only record that rocks of the southern part probably also experienced an early non eclogitic high pressure metamorphism

far field effects of late miocene subduction in the eastern carpathians e w compression and inversion of structures in the alpine carpathian pannonian region kinematic and paleostress data constrain a late miocene e w compressional event that affected the entire alpine carpathian pannonian system after 9 ma and prior to 5 3 ma the maximum horizontal compression directions obtained from 110 stations show a mean 1 orientation of 083 deformation is mainly strike slip e w directed compression followed early to middle miocene upper plate extension in the pannonian basin which was caused by the retreating subduction boundary in the outer carpathians this compressional event terminated early to middle miocene eastward lateral extrusion of the eastern alps and reverted strike slip faults which bounded earlier extruded wedges such as the salzachtal ennstal fault the periadriatic fault the mur murz vienna basin fault system and strike slip faults in the western carpathians e w compression caused the reorientation of the extension direction of the alpine crustal stack east directed tectonic unroofing of the metamorphic domes in the central eastern alps terminated between 9 and 6 ma and early to middle miocene orogen parallel e w extension switched to late miocene n s extension which parallels modern topographic slopes in the pannonian basin the change from synrift extension to late miocene compression during the postrift phase caused the pronounced postrift subsidence by stress induced downward flexure of the loaded lithosphere we relate late miocene e w compression to coeval late stage west directed subduction of the european plate below the eastern carpathians slab pull of the subducted plate caused subduction roll back and upper plate extension of the pannonian area up to the middle miocene subduction slowed down and ceased when up to 60 km thick buoyant continental crust entered the subduction zone during the short period of continued convergence e w directed compressive stress was transmitted across the subduction boundary into the upper plate compressive stress was transferred through the uppermost brittle crust of the earlier extended pannonian region into the eastern alps up to 1400 km behind the subduction zone e w compression terminated during the pliocene when the pliocene to recent nnw sse compressive stress field was established in central europe

reply to the comment of fugenschuh et al on the paper estimating displacement along the brenner fault and orogen parallel extension in the eastern alps by rosenberg and garcia int j earth sci geol rundsch 2011 100 1129 1145 fugenschuh et al 2011 question several aspects of our paper rosenberg and garcia 2011 on the estimate of extension along the brenner fault bf first they emphasize the necessity of a two phase extensional model to understand exhumation of the footwall of the bf second they claim that the vertical offsets and extensional displacement calculated by rosenberg and garcia 2011 only refer to the brittle phase of the bf third they follow the new interpretations of tochterle et al 2011 inferring that the continuation of the brenner ductile mylonites is located along the north western border of the tauern window tw fourth they present a new estimate of extension and of exhumation by folding and erosion based on the quantification of tectonic omissions we discuss and reply to these four issues below

evidence for east west crustal extension in the eastern alps implications for the unroofing history of the tauern window the contact between the western border of the tauern window and the overlying austroalpine nappes austria and italy is marked by a structural petrologic and geochronologic discontinuity that developed in the early stages of unroofing of the window within the window pressure temperature time paths j selverstone 1985 indicate that significant ductile thinning occurred shortly after the cessation of thrusting paleocene eocene sense of shear indicators rotated porphyroblasts asymmetric augen and pressure shadows s c fabrics associated with a west plunging stretching lineation indicate that this thinning occurred in response to top to the west low angle normal shear during metamorphism the same sense of normal shear is present in the mesozoic members of the austroalpine sequence west of the window in these rocks however west directed shear occurred at low temperatures 300 c after the thermal peak of metamorphism structural data and the regional geometry imply that the western end of the tauern window is a low angle normal fault brenner line that juxtaposed brittlely deformed rocks of the austroalpine nappes against more ductilely deformed rocks from the window biotite k ar and rb sr data suggest a miocene age for final movement on the brenner line these data indicate a prolonged history of east west extension in the eastern alps that affected all crustal levels early ductile thinning of lower crust followed by mid to upper crustal low angle normal faulting a model is presented that relates the young east west extension to displacement transfer from dextral movement on the periadriatic lineament in this model the brenner line and by analogy the simplon line can be thought of as detachment faults that tectonically unroofed the tauern window and lepontine thermal highs respectively

transition from orogen perpendicular to orogen parallel exhumation and cooling during crustal indentation key constraints from 147sm 144nd and 87rb 87sr geochronology tauern window alps abstract the core of the alpine orogen in the eastern alps tauern window experienced a change from orogen normal shortening and post nappe doming to predominantly orogen parallel extension and tectonic unroofing during late oligocene to miocene northward indentation of the adriatic microplate a new 147 sm 144 nd isochron age of 25 7 0 9 ma on a garnet bearing assemblage from the lowest nappe complex forming a dome in the eastern part of the tauern window indicates that high temperatures related to post nappe barrovian type metamorphism overlapped in time with the onset of doming new 87 rb 87 sr biotite ages from this same complex combined with previously published 87 rb 87 sr white mica ages suggest that doming and exhumation began no later than 28 ma immediately in front of indenting austroalpine crustal blocks then migrated laterally to the ese during rapid exhumation and orogen parallel stretching beginning at about 23 ma rapid cooling ended at approximately 17 ma in the footwall of the katschberg normal fault which delimits the eastern margin of the tauern window a similar pattern of migrating doming orogen parallel extension and cooling is recognized in the western part of the tauern window where rapid exhumation began at about 20 ma some 2 3 ma later than in the eastern part this difference in the onset of rapid exhumation as well as the overall migration of doming from the center to the ends of the tauern window are attributed to fragmentation of the aforementioned austroalpine blocks along the leading edge of the main adriatic indenter southern alps as this indenter advanced to the north

the dachstein paleosurface and the augenstein formation in the northern calcareous alps a mosaic stone in the geomorphological evolution of the eastern alps the central and eastern areas of the northern calcareous alps nca are characterized by remnants of the dachstein paleosurface which formed in late eocene to early oligocene time and is preserved with limited modification on elevated karst plateaus in oligocene time the dachstein paleosurface subsided and was sealed by the augenstein formation a terrestrial succession of conglomerates and sandstones which are only preserved in small remnants on the plateaus some in an autochthonous position thermochronological data suggest a maximum thickness of the augenstein formation of 1 3 km possibly 2 km the age of the augenstein formation is constrained by the overall geological situation as early oligocene to earliest miocene fission track age data support an early oligocene age of the basal parts of the formation the source area of the augenstein formation consisted predominantly of weakly metamorphic paleozoic terrains greywacke zone and equivalents as well as the late carboniferous to scythian siliciclastic base of the nca to the south of the depositional area to the west the augenstein formation interfingered with the tertiary deposits of the inntal sedimentation of the augenstein formation was terminated in early miocene time in the course of the orogenic collapse of the eastern alps the augenstein sediments were eroded and redeposited in the foreland molasse zone from pannonian times 10 ma on the nca and the denuded dachstein surface experienced uplift in several pulses the dachstein paleosurface has been preserved in areas in which thick limestone sequences allowed subsurface erosion by cave formation and thus prevented major surface erosion

fault slip analysis and late exhumation of the tauern window eastern alps exhumation of the eastern alps from the early tertiary to the late miocene was localized mainly in the tauern window a thermal and structural dome located in front of the dolomites indenter stress inversions based on new structural investigations over the entire tauern window indicate a regional zoning of the paleostress field with a predominance of strike slip states of stress in the core of the investigated area and dominant extensional regimes in the eastern and western borders of the dome few inverse fault structures have been highlighted we propose a two stage deformation history in order to explain the different types of structures that characterise the ductile and the brittle domains during the first stage of exhumation of the tauern window corresponding to the folding event the brittle crust was probably dominated by n s shortening and compression the second stage of exhumation was marked by normal faulting at the borders of the dome and strike slip faulting in the core during the second stage the brittle part of the crust that was previously affected by compressive structures belonging to the first stage was eroded normal faulting associated to e w extension along the eastern and western borders of the tauern window was accommodated by strike slip faulting located in the core of the tauern window yielding e w extension and n s shortening the orientation of the extensional axes and the nature of the stress tensors are similar to the ones inferred for the late stage brittle overprint of the internal basement massifs of the central alps pointing to a possible common large scale state of stress acting well beyond the area of the eastern alps

alpine metamorphism in the south east tauern window austria 2 rates of heating cooling and uplift existing geochronological data are reviewed and new rb sr k ar and 39ar 40ar ages are presented including a suite of 33 mica ages from a 20 km north south tunnel section these data are discussed in relation to the thermal history from the overthrusting of the autroalpine nappes c 65 myr ago to the present the earliest phase of metamorphism involving lawsonite crystallization is associated with emplacement of these nappes subsequently temperatures in the rocks beneath rose at a mean rate of 3 6 c myr until the climax of metamorphism at high structural levels published data indicate an age 35 myr for the metamorphic climax in contrast a new 39ar 40ar step heating age of 23 8 0 8 myr on amphibole from near the base of peripheral schieferhulle closely approximates the age of metamorphism and provides the first clear indication that the climax of metamorphism occurred later at deeper structure levels following the climax near isothermal uplift and erosion reduced pressure to c 1 kbar before white mica closure at 19 myr this implies uplift at 3 mm yr along the tunnel section white mica k ar ages vary systematically from 24 myr to 16 5 myr with position relative to a late 4 km amplitude dome whereas biotite rb sr ages are uniform at 16 5 myr across the whole profile doming is thus dated at 16 5 myr with transient uplift rates 5 mm yr at other times uplift rates were 1 mm yr

balancing lateral orogenic float of the eastern alps abstract oligocene to miocene post collisional shortening between the adriatic and european plates was compensated by frontal thrusting onto the molasse foreland basin and by contemporaneous lateral wedging of the austroalpine upper plate balancing of the upper plate shortening by horizontal retrodeformation of lateral escaping and extruding wedges of the austroalpine lid enables an evaluation of the total post collisional deformation of the hangingwall plate quantification of the north south shortening and east west extension of the upper plate is derived from displacement data of major faults that dissect the austroalpine wedges indentation of the south alpine unit corresponds to 64 km north south shortening and a minimum of 120 km of east west extension lateral wedging affected the eastern alps east of the giudicarie fault west of the giudicarie fault north south shortening was compensated by 50 to 80 km of backthrusting in the lombardian thrust system of the southern alps the main structures that bound the escaping wedges to the north are the inntal fault system ca 50 km sinistral offset the konigsee lammertal traunsee klt fault 10 km and the salzach ennstal mariazell puchberg semp fault system 60 km these faults as well as a number of minor faults with displacements less than 10 km root in the basal detachment of the alps the thin skinned nature of lateral escape related structures north of the semp line is documented by industry reflection seismic lines crossing the northern calcareous alps nca and the frontal thrust of the eastern alps complex triangle zones with passive roof backthrusts of middle miocene molasse sediments formed in front of the laterally escaping wedges of the northern eastern alps the aim of this paper is a semiquantitative reconstruction of the upper plate of the eastern alps most of the data is published elsewhere

syn metamorphic folding in the tauern window austria dated by th pb ages from individual allanite porphyroblasts high precision 232th 208pb dates have been obtained from allanite porphyroblasts that show unambiguous microstructural relationships to fabrics in a major syn metamorphic fold in the se tauern window austria three porphyroblasts were analysed from a single garnet mica schist from the peripheral schieferhulle in the core of the ankogel synform one of a series of folds which developed shortly before the thermal peak of alpine epidote amphibolite facies metamorphism allanite grain 1 provided two analyses with a combined age of 27 7 0 7 ma grain 2 which was slightly bent and fractured during crenulation provided two analyses with a combined age of 27 7 0 4 ma a single analysis from grain 3 which overgrew an already crenulated fabric gave an age of 28 0 1 4 ma the five 232th 208pb ages agree within error and define an isochron with an age of 27 71 0 36 ma 95 confidence level mswd 0 46 the results imply that the crenulation event was in progress in a short interval 1 ma c 28 ma and that the ankogel synform was forming at this time the thermal peak of regional metamorphism in the se tauern window was probably attained shortly after 28 ma only c 5 ma after eclogite facies metamorphism in the central tauern window metasediment may contain allanite porphyroblasts with clear cut microstructural relationships to fabric development and metamorphic crystallization for such rocks 232th 208pb dating on microsamples offers a powerful geochronological tool

why allanite may swindle about its true age allanite from the tertiary rieserferner pluton austrian alps is texturally and chemically heterogeneous continuous covariation trends reflect coupled substitution of ca al vs fe ree th in allanite whereas systematic variations in la nd demonstrate the increasingly stronger depletion of lree in the melt during its crystallization allanite samples corrected for 206pbexcess from two rocks scatter in the concordia diagram and define discordias from 31 8 0 4 ma and 32 2 0 4 ma to ca 540 ma the apparent inheritance does not originate from the inclusion of older allanite or a high phase such as monazite xenotime or zircon but from the incorporation of radiogenic pb originating from a precursor since allanite requires a high enrichment of th u and lree it may form at the expense of a th lree rich precursor in metamorphic rocks or where such a phase had dissolved in melts likely precursors acquire with time radiogenic pb isotopic compositions this pb if incorporated in the product mineral may give the illusion of inheritance the allanite samples from the rieserferner pluton show a tendency from high th ucalc 30 50 in samples with an alpine age to low th ucalc 4 12 in samples with distinct inheritance this relation between extent of inheritance and apparent th ucalc indicates a lower th ucalc for a possible precursor falling into the th u range commonly encountered for monazite precursor monazite would have originated from assimilated palaeozoic rocks and give rise to localized enrichments of th and lree in the melt thus eventually enabling the growth of allanite

are the alps collapsing abstract orogenic collapse is a process that transfers gravitational potential energy from regions of high potential energy to regions of lower potential energy this transfer is classically considered to be accomplished by extension in the orogenic core and by synchronous shortening in foreland regions of the orogen not all extensional features in collisional mountain belts need however reflect orogenic collapse normal faulting thrust faulting and strike slip faulting are all active in different parts of the alps today and reflect complex local responses to ongoing europe adria convergence the western alps is the only area today where extension and shortening radial to orogen trend occur synchronously and where orogenic collapse may be an important process elsewhere in the alps normal faults are oriented at a high angle to orogen trend and were primarily active in oligocene and miocene time most present day activity in the central and eastern alps is on strike slip faults that are accommodati

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

balancing cross sections with kinematic constraints the dolomites northern italy balancing of structural cross sections is often hindered by a limited database or tectonic complications in such cases kinematic constraints may help to better constrain the construction of a cross section and its extrapolation to depth the kinematic implications of a known structure generally at the surface have to be considered for the unknown structure and for the internal consistency of a cross section a key point is the quantification of shortening of the known structure the extrapolation of this parameter allows balancing in an approximate way emphasizing major structures while minor structures are either neglected or treated in a simplified way with this approach a quick overview can be achieved on how much leeway for interpretation exists critical points for testing various working hypotheses become more evident and the trial and error effort during the construction of a balanced section is considerably shortened still the implications the observed structures have on the deeper crustal levels can be assessed this concept is applied to a section across the italian dolomites a brittle fold and thrust belt lacking reflection seismic data so far and thus with a poorly known deep structure still active south vergent alpine thrusting is oriented approximately perpendicular to previous dinaric thrusting the ramp flat style is dominant due to rheological constrasts within the stratigraphic sequence thanks to kinematic balancing based on surface data three alpine thrust systems could be identified each defining a thrust sheet with its particular basement unit and its sedimentary part superposition of the two more external basement units led to the presently observed high elevation of the triassic sequence in the dolomites shortening since late miocene times amounts to more than 50 km retrodeformation of alpine thrusting is a key for better understanding the previous dinaric structures and kinematics