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In the frame of the AlpArray project we analyze teleseismic data from permanent and temporary stations of the greater Alpine region to study seismic discontinuities down to about 140 km depth. We average broadband teleseismic S waveform data to retrieve S-to-P converted signals from below the seismic stations. In order to avoid processing artefacts, no deconvolution or filtering is applied and S arrival times are used as reference. We show a number of north-south and east-west profiles through the greater Alpine area. The Moho signals are always seen very clearly, and also negative velocity gradients below the Moho are visible in a number of profiles. A Moho depression is visible along larger parts of the Alpine chain. It reaches its largest depth of 60 km beneath the Tauern Window. The Moho depression ends however abruptly near about 13° E below the eastern Tauern Window. The Moho depression may represent the mantle trench, where the Eurasian lithosphere is subducted below the Adriatic lithosphere. East of 13° E an important along-strike change occurs; the image of the Moho changes completely. No Moho deepening is found in this easterly region; instead the Moho is updoming along the contact between the European and the Adriatic lithosphere all the way into the Pannonian Basin. An important along strike change was also detected in the upper mantle structure at about 14° E. There, the lateral disappearance of a zone of negative P-wave velocity gradient indicates that the S-dipping European slab laterally terminates east of the Tauern Window in the axial zone of the Alps. The area east of about 13° E is known to have been affected by severe late-stage modifications of the structure of crust and uppermost mantle during the Miocene when the ALCAPA (Alpine, Carpathian, Pannonian) block was subject to E-directed lateral extrusion.

In the frame of the AlpArray project we analyse teleseismic data from permanent and temporary stations of the Alpine region to study seismic discontinuities down to about 140 km depth. We average broadband teleseismic S-waveform data to retrieve S-to-P converted signals from below the seismic stations. In order to avoid processing artefacts, no deconvolution or filtering is applied, and S arrival times are used as reference for stacking. We show a number of north-south and east-west profiles through the Alpine area. The Moho signals are always seen very clearly, and negative velocity gradients below the Moho depth are also visible in a number of profiles. A Moho depression is visible along larger parts of the Alpine chain. It reaches its largest depth of 60 km beneath the Tauern Window. However, the Moho depression ends abruptly near about 13'E below the eastern Tauern Window. This Moho depression may represent the crustal trench, where the Eurasian lithosphere is subducted below the Adriatic lithosphere. East of 13'E an important along-strike change occurs; the image of the Moho changes completely. No Moho deepening is found in this easterly region; instead the Moho bends up along the contact between the European and the Adriatic lithosphere all the way to the Pannonian Basin. An important along-strike change was also detected in the upper mantle structure at about 14'E. There, the lateral disappearance of a zone of negative velocity gradient in the uppermost mantle indicates that the S-dipping European slab laterally terminates east of the Tauern Window in the axial zone of the Alps. The area east of about 13'E is known to have been affected by severe late-stage modifications of the structure of crust and uppermost mantle during the Miocene when the ALCAPA (Alpine, Carpathian, Pannonian) block was subject to E-directed lateral extrusion., Solid Earth, 12 (11), ISSN:1869-9510, ISSN:1869-9529

Based on recent results of AlpArray, we propose a new model of Alpine collision that involves subduction and detachment of thick (∼ 180 km) European lithosphere. Our approach combines teleseismic P-wave tomography and existing local earthquake tomography (LET), allowing us to image the Alpine slabs and their connections with the overlying orogenic lithosphere at an unprecedented resolution. The images call into question the conventional notion that downward-moving lithosphere and slabs comprise only seismically fast lithosphere. We propose that the European lithosphere is heterogeneous, locally containing layered positive and negative Vp anomalies of up to 5 %–6 %. We attribute this layered heterogeneity to seismic anisotropy and/or compositional differences inherited from the Variscan and pre-Variscan orogenic cycles rather than to thermal anomalies. The lithosphere–asthenosphere boundary (LAB) of the European Plate therefore lies below the conventionally defined seismological LAB. In contrast, the lithosphere of the Adriatic Plate is thinner and has a lower boundary approximately at the base of strong positive Vp anomalies at 100–120 km. Horizontal and vertical tomographic slices reveal that beneath the central and western Alps, the European slab dips steeply to the south and southeast and is only locally still attached to the Alpine lithosphere. However, in the eastern Alps and Carpathians, this slab is completely detached from the orogenic crust and dips steeply to the north to northeast. This along-strike change in attachment coincides with an abrupt decrease in Moho depth below the Tauern Window, the Moho being underlain by a pronounced negative Vp anomaly that reaches eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted as representing hot upwelling asthenosphere that heated the overlying crust, allowing it to accommodate Neogene orogen-parallel lateral extrusion and thinning of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the east. A European origin of the northward-dipping, detached slab segment beneath the eastern Alps is likely since its down-dip length matches estimated Tertiary shortening in the eastern Alps accommodated by originally south-dipping subduction of European lithosphere. A slab anomaly beneath the Dinarides is of Adriatic origin and dips to the northeast. There is no evidence that this slab dips beneath the Alps. The slab anomaly beneath the Northern Apennines, also of Adriatic origin, hangs subvertically and is detached from the Apenninic orogenic crust and foreland. Except for its northernmost segment where it locally overlies the southern end of the European slab of the Alps, this slab is clearly separated from the latter by a broad zone of low Vp velocities located south of the Alpine slab beneath the Po Basin. Considered as a whole, the slabs of the Alpine chain are interpreted as highly attenuated, largely detached sheets of continental margin and Alpine Tethyan oceanic lithosphere that locally reach down to a slab graveyard in the mantle transition zone (MTZ)., Solid Earth, 12 (11), ISSN:1869-9510, ISSN:1869-9529

We present a map that correlates tectonic units between Alps and western Turkey accompanied by a text providing access to literature data, explaining the concepts used for defining the mapped tectonic units, and first-order paleogeographic inferences. Along-strike similarities and differences of the Alpine-Eastern Mediterranean orogenic system are discussed. The map allows (1) for superimposing additional information, such as e.g., post-tectonic sedimentary basins, manifestations of magmatic activity, onto a coherent tectonic framework and (2) for outlining the major features of the Alpine-Eastern Mediterranean orogen. Dinarides-Hellenides, Anatolides and Taurides are orogens of opposite subduction polarity and direction of major transport with respect to Alps and Carpathians, and polarity switches across the Mid-Hungarian fault zone. The Dinarides-Hellenides-Taurides (and Apennines) consist of nappes detached from the Greater Adriatic continental margin during Cretaceous and Cenozoic orogeny. Internal units form composite nappes that passively carry ophiolites obducted in the latest Jurassic–earliest Cretaceous or during the Late Cretaceous on top of the Greater Adriatic margin successions. The ophiolites on top of composite nappes do not represent oceanic sutures zones, but root in the suture zones of Neotethys that formed after obduction. Suturing between Greater Adria and the northern and eastern Neotethys margin occupied by the Tisza and Dacia mega-units and the Pontides occurred in the latest Cretaceous along the Sava-Izmir-Ankara-Erzincan suture zones. The Rhodopian orogen is interpreted as a deep-crustal nappe stack formed in tandem with the Carpatho-Balkanides fold-thrust belt, now exposed in a giant core complex exhumed in late Eocene to Miocene times from below the Carpatho-Balkan orogen and the Circum-Rhodope unit. Its tectonic position is similar to that of the Sakarya unit of the Pontides. We infer that the Rhodope nappe stack formed due to north-directed thrusting. Both Rhodopes and Pontides are suspected to preserve the westernmost relics of the suture zone of Paleotethys.

Central Anatolia exposes previously buried and metamorphosed, continent-derived rocks – the Kirsehir and Afyon zones – now covering an area of ∼300 × 400 km. So far, the exhumation history of these rocks has been poorly constrained. We show for the first time that the major, >120 km long, top-NE ‘Ivriz’ Detachment controlled the exhumation of the HP/LT metamorphic Afyon Zone in southern Central Anatolia. We date its activity at between the latest Cretaceous and early Eocene times. Combined with previously documented isolated extensional detachments found in the Kirsehir Block, our results suggest that a major province governed by extensional exhumation was active throughout Central Anatolia between ∼80 and ∼48 Ma. Although similar in dimension to the Aegean extensional province to the east, the Central Anatolian extensional province is considerably older and was controlled by a different extension direction. From this, we infer that the African slab(s) that subducted below Anatolia must have rolled back relative to the Aegean slab since at least the latest Cretaceous, suggesting that these regions were underlain by a segmented slab. Whether or not these early segments already corresponded to the modern Aegean, Antalya, and Cyprus slab segments remains open for debate, but slab segmentation must have occurred much earlier than previously thought.

Multichronometric analyses were performed on samples from a transect in the French-Italian Western Alps crossing nappes derived from the Briançonnais terrane and the Piemonte-Liguria Ocean, in an endeavour to date both high-pressure (HP) metamorphism and retrogression history. Twelve samples of white mica were analysed by 39Ar-40Ar stepwise heating, complemented by two samples from the Monte Rosa nappe 100 km to the NE and also attributed to the Briançonnais terrane. One Sm-Nd and three Lu-Hf garnet ages from eclogites were also obtained. White mica ages decrease from c. 300 Ma in the westernmost samples (Zone Houillère), reaching c. 300°C during Alpine metamorphism, to 6·45 atoms per formula unit increases eastward. Across the whole traverse, phengitic mica grown during HP metamorphism defines the D1 foliation. Syn-D2 mica is more Si-poor and associated with nappe stacking, exhumation, and hydrous retrogression under greenschist-facies conditions. Syn-D1 phengite is very often corroded, overgrown by, or intergrown with, syn-D2 muscovite. Most importantly, syn-D2 recrystallization is not limited to S2 schistosity domains; micrometre-scale chemical fingerprinting reveals muscovite pseudomorphs after phengite crystals, which could be mistaken for syn-D1 mica based on microstructural arguments alone. The Cl/K ratio in white mica is a useful discriminator, as D2 retrogression was associated with a less saline fluid than eclogitization. As petrology exerts the main control on the isotope record, constraining the petrological and microstructural framework is necessary to correctly interpret the geochronological data, described in both the present study and the literature. Our approach, which ties geochronology to detailed geochemical, petrological and microstructural investigations, identifies 47-48 Ma as the age of HP formation of syn-D1 mica along the studied transect and in the Monte Rosa area. Cretaceous apparent mica ages, which were proposed to date eclogitization by earlier studies based on conventional ‘thermochronology', are due to Ar inheritance in incompletely recrystallized detrital mica grains. The inferred age of the probably locally diachronous, greenschist-facies, low-Si, syn-D2 mica ranges from 39 to 43 Ma. Coexistence of D1 and D2 ages, and the constancy of non-reset D1 ages along the entire transect, provides strong evidence that the D1 white mica ages closely approximate formation ages. Volume diffusion of Ar in white mica (activation energy E = 250 kJ mol−1; pressure-adjusted diffusion coefficient D'0 < 0·03 cm2 s−1) has a subordinate effect on mineral ages compared with both prograde and retrograde recrystallization in most samples

Swiss Journal of Geosciences, 110 (2), ISSN:1661-8734, ISSN:1661-8726

The construction of five crustal-scale profiles across the Western Alps and the Ivrea mantle wedge integrates up-to-date geological and geophysical information and reveals important along strike changes in the overall structure of the crust of the Western Alpine arc. Tectonic analysis of the profiles, together with a review of the existing literature allows for proposing the following multistage evolution of the arc of the Western Alps: (1) exhumation of the mantle beneath the Ivrea Zone to shallow crustal depths during Mesozoic is a prerequisite for the formation of a strong Ivrea mantle wedge whose strength exceeds that of surrounding mostly quartz-bearing units, and consequently allows for indentation of the Ivrea mantle wedge and eastward back-thrusting of the western Alps during Alpine orogeny. (2) A first early stage (pre-35 Ma) of the West-Alpine orogenic evolution is characterized by top-NNW thrusting in sinistral transpression causing at least some 260 km displacement of internal Western Alps and E-W-striking Alps farther east, together with the Adria micro-plate, towards N to NNW with respect to stable Europe. (3) The second stage (35–25 Ma), further accentuating the arc, is associated with top-WNW thrusting in the external zones of the central portion of the arc and is related to the lateral indentation of the Ivrea mantle slice towards WNW by some 100–150 km. (4) The final stage of arc formation (25–0 Ma) is associated with orogeny in the Apennines leading to oroclinal bending in the southernmost Western Alps in connection with the 50° counterclockwise rotation of the Corsica-Sardinia block and the Ligurian Alps. Analysis of existing literature data on the Alps–Apennines transition zone reveals that substantial parts of the Northern Apennines formerly suffered Alpine-type shortening associated with an E-dipping Alpine subduction zone and were backthrusted to the NE during Apenninic orogeny that commences in the Oligocene.

The waning stage(s) of the Tethyan ocean(s) in the Balkans are not well understood. Controversy centres on the origin and life-span of the Cretaceous Sava Zone, which is allegedly a remnant of the last oceanic domain in the Balkan Peninsula, defining the youngest suture between Eurasia- and Adria-derived plates. In order to investigate to what extent Late-Cretaceous volcanism within the Sava Zone is consistent with this model we present new age data together with trace-element and Sr–Nd– Pb isotope data for the Klepa basaltic lavas from the central Balkan Peninsula. Our new geochemical data show marked differences between the Cretaceous Klepa basalts (Sava Zone) and the rocks of other volcanic sequences from the Jurassic ophiolites of the Balkans. The Klepa basalts mostly have Sr–Nd–Pb isotopic and trace-element signatures that resemble enriched within-plate basalts substantially different from Jurassic ophiolite basalts with MORB, BAB and IAV affinities. Traceelement modelling of the Klepa rocks indicates 2%–20% polybaric melting of a relatively homogeneously metasomatised mantle source that ranges in composition from garnet lherzolite to ilmenite+apatite bearing spinel–amphibole lherzolite. Thus, the residual mineralogy is characteristic of a continental rather than oceanic lithospheric mantle source, suggesting an intracontinental within-plate origin for the Klepa basalts. Two alternative geodynamic models are internally consistent with our new findings: (1) if the Sava Zone represents remnants of the youngest Neotethyan Ocean, magmatism along this zone would be situated within the forearc region and triggered by ridge subduction; (2) if the Sava Zone delimits a diffuse tectonic boundary between Adria and Europe which had already collided in the Late Jurassic, the Klepa basalts together with a number of other magmatic centres represent volcanism related to transtensional tectonics.

The Sava Zone of the northern Dinarides is part of the Cenozoic Adria-Europe plate boundary. Here Late Cretaceous subduction of remnants of Meliata-Vardar oceanic lithosphere led to the formation of a suture, across which upper plate European-derived units of Tisza-Dacia were juxtaposed with Adria-derived units of the Dinarides. Late Cretaceous siliciclastic sediments, deposited on the Adriatic plate, were incorporated into an accretionary wedge that evolved during the initial stages of continent-continent collision. Structurally deeper parts of the exposed accretionary wedge underwent amphibolite-grade metamorphism. Grt-Pl-Ms-Bt thermobarometry and multiphase equilibria indicate temperatures between 550 degrees C and 630 degrees C and pressures between 5 and 7 kbar for this event. Peak metamorphic conditions were reached at around 65 Ma. Relatively slow cooling from peak metamorphic conditions throughout most of the Paleogene was possibly induced by hanging wall erosion in conjunction with southwest directed propagation of thrusting in the Dinarides. Accelerated cooling took place in Miocene times, when the Sava Zone underwent substantial extension that led to the exhumation of the metamorphosed units along a low-angle detachment. Footwall exhumation started under greenschist facies conditions and was associated with top-to-the-north tectonic transport, indicating exhumation from below European plate units. Extension postdates the emplacement of a 27 Ma old granitoid that underwent solid-state deformation under greenschist facies conditions. The (40)Ar/(39)Ar sericite and zircon and apatite fission track ages from the footwall allow bracketing this extensional unroofing between 25 and 14 Ma. This extension is hence linked to Miocene rift-related subsidence in the Pannonian basin, which represents a back-arc basin formed due to subduction roll-back in the Carpathians.

The investigated HP/LT metasedimentary units of the Valaisan and adjacent European domains occupy a key position in the Alpine belt for understanding the transition from early subduction-related HP/LT metamorphism to collision-related Barrovian overprint and the evolution of mountain belts in general. The timing of high-pressure metamorphism, subsequent retrogression and following Barrow-type overprint was studied by 40Ar/39Ar dating of biotite and several white mica generations that are well characterized in terms of mineral chemistry, texture and associated mineral assemblages. Four distinct age populations of white mica record peak pressure conditions (42–40 Ma) and several stages of subsequent retrograde metamorphic evolution (36–25 Ma). Biotite isotopic analyses yield consistent apparent ages that cluster around 18–16 Ma for the Barrow-type thermal overprint. The recorded isotopic data reveal a significant time gap in the order of some 20 Ma between subduction-related HP/LT metamorphism and collision-related Barrovian overprint, supporting the notion of a polymetamorphic evolution associated with a bimodal P-T path.

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The interplay between slab dynamics and intraplate stresses in postcollisional times creates large near-surface deformation, particularly in highly bent orogens with significant lateral variations in mechanical properties. This deformation is expressed through abnormal foredeep geometries and contrasting patterns of vertical movements. Intraplate folding is often the controlling mechanism, particularly when the orogenic belt is locked. The study of these tectonic processes in the SE Carpathians indicates a generalized subsidence period during latest MiocenePliocene times driven by the slab-pull and an intraplate folding due to an overall Quaternary inversion. The latter accommodates 5 km ESE-ward movement of this area with respect to the neighboring units, which creates complicated threedimensional deformation patterns potentially driven at a larger scale by the interaction between the Adriatic indentor and the entire Carpathians system. The lithospheric anisotropy inherited from the subduction times concentrates strain and induces large-scale deformation far away from the active plate margins. This anisotropy is dynamic because of deep mantle processes related to the subducted slab during postcollisional times, such as thermal reequilibration or increase in slab dip.

The study is devoted to the tectono-metamorphic and magmatic evolution of the Internal Dinarides and it furthermore addresses the geodynamic evolution of the Balkan Peninsula. The investigated area is located in the internal-most part of the Dinarides and covers the contact zone between the Dinaridic orogen that essentially formed in Latest Cretaceous to Paleogene times and the “Serbo–Macedonian Massif“, that is a part of the Carpatho–Balkan orogen (Dacia Mega-Unit) which is characterised by older (pre-Turonian) deformations. The widespread occurrences of ophiolitic rocks, separated by different fragments of continental basement rocks led to a ,multi-ocean‘ concept whereby the oceans were separated by elongate continental terranes or micro-plates. By investigating the stratigraphic and tectonic evolution of the various continent-derived units and by studying their relation with the intervening ophiolitic belts this ,multi-terrane/multi-ocean‘ problem is critically addressed and a one-ocean model is preferred. Thereby the continental terranes simply represent the passive margin of Adria, exposed in windows below the ophiolites, which were obducted in Late Jurassic times. Strongly deformed and metamorphosed meta-sediments crop out in the Studenica valley and the Kopaonik area representing the easternmost occurrences of Triassic sediments within the Dinarides. Upper Paleozoic terrigeneous sediments are overlain by Lower Triassic siliciclastics and limestones, followed by Anisian shallow-water carbonates. A pronounced facies change to hemipelagic and distal turbiditic, cherty meta-limestones (Kopaonik Formation) testifies to a late Anisian drowning of the former shallow-water carbonate shelf. Sedimentation of the Kopaonik Formation was contemporaneous with shallow-water carbonate production on nearby and more proxi- mal carbonate platforms that were the source areas of diluted turbidity currents reaching the depositional area of this formation. The Kopaonik Formation was dated by conodont faunas as late Anisian to Norian and possibly extends into the Early Jurassic. It is therefore considered an equivalent of the grey Hallstatt facies of the Eastern Alps, the Western Carpathians and the Albanides–Hellenides. The coeval carbonate platforms were generally located in more proximal areas of the Adriatic margin, whereas the distal margin was dominated by hemipelagic/ pelagic and distal turbiditic sedimentation, facing the evolving Neotethys Ocean to the east. A similar arrangement of Triassic facies belts can be recognised all along the evolving Meliata–Maliac–Vardar branch of Neotethys, which is in line with a ‘one-ocean-hypothesis’ for the Dinarides: all ophiolites presently located southwest of the Drina–Ivanjica and Kopaonik thrust sheets are derived from an area to the east, and the Drina–Ivanjica and Kopaonik units emerge in tectonic windows from below this ophiolite nappe. On the base of the Triassic facies distribution neither arguments for an independent Dinaridic Ocean nor evidence for isolated terranes or blocks was seen. Two age groups for the Cenozoic granitoids in the Dinarides of southern Serbia were determined by high precision single grain U–Pb dating of thermally annealed and chemically abraded zircons: (i) Oligocene ages (Ko- paonik, Drenje, Željin) ranging from 31.7 to 30.6 Ma and (ii) Miocene ages (Golija and Polumir) at 20.58–20.17 and 18.06–17.74 Ma, respectively. Apatite fission-track central ages and modelling combined with zircon central ages, together with local structural observations, constrain the subsequent exhumation history of the magmatic rocks. They indicate rapid cooling from above 300 to ca. 80 °C between 16 and 10 Ma for the Oligocene and the Miocene age group, caused by extensional exhumation of the plutons that are located in the footwall of core-complexes. Miocene magmatism and core-complex formation thus not only affected the Pannonian basin but also a part of the mountainous areas of the internal Dinarides. Four different deformation phases (D1–D4) are distinguished in the study area. D1 to D3 are related to com- pression and metamorphism that pre-date the intrusion of I-type Oligocene plutons in Early Oligocene times, whereas the fourth deformation phase (D4) is related to extensional tectonics and exhumation that are contempo- raneous with the intrusion of Miocene S-type granitoids. The first event (D1) is probably linked to the obduction of the Western Vardar Ophiolitic Unit onto the distal Adriatic continental margin. It is associated with top-NW shear-senses observed in sigma-clasts in a ductilely deformed and slightly metamorphosed ophiolitic mélange as well as with a penetrative foliation and a stretching lineation coupled to greenschist facies metamorphism in the Late Paleozoic to Early Jurassic sediments. During the Late Cretaceous (110–85 Ma) these sediments witnessed a metamorphic event that occurred under lowermost greenschist-facies conditions, associated with the ductile deformation phase (D2) represented by a well developed foliation and isoclinal folds overprinting D1. A higher greenschist- to amphibolite-facies overprint is observed during Middle to Late Eocene (45–35 Ma) due to nappe- stacking caused by out-of-sequence thrusting (D3). This event is associated with the E–W-oriented compression related to and following the closure of the Sava suture. During the Miocene the entire area of investigation un- derwent rapid exhumation, accompanied by intense N–S-oriented ductile stretching (D4). This extension is correlated with the Miocene extension in the Pannonian basin whose location is in the back-arc area of the W-directed subduction of the European lithosphere beneath the Carpathians.

This study analyses the tectono-metamorphic evolution of metasedimentary units belonging to the Valaisan and adjacent European domains at the north-eastern border of the Lepontine dome (Central Alps). The investigated area is characterized by a remarkable metamorphic gradient ranging from subduction-related HP/LT metamorphism in the NE to collision-related Barrovian overprint in the SW. Detailed structural fieldwork and petrological investigations including Raman spectroscopy of carbonaceous matter were carried out in order to reconstruct the tectono-metamorphic evolution on a larger scale. Furthermore, new 40Ar/39Ar dating of white mica and biotite reveal the timing of both subductionrelated high-pressure metamorphism and collision-related Barrovian overprint. The combination of all these investigations allows for deciphering a complete P-T-d-t path (pressure, temperature, deformation and time) of an area that occupies a key position in the Alpine orogenic belt for understanding the transition from subduction to collision. This study documents for the first time that relics of Fe-Mg carpholite indicating blueschist facies conditions occur also within metasedimentary units that are part of the north-eastern Lepontine dome where, so far, exclusively Barrovian assemblages were found. They occur in metasediments from both the Valaisan domain (Grava and Tomül nappes) and parts of the adjacent European domain (Peiden slices and Piz Terri-Lunschania unit). These high-pressure units were subsequently overprinted by a thermal event, as is documented by the growth of new minerals typical for Barrovian metamorphism. The investigated metasediments provide clear evidence for a bimodal P-T path in the north-eastern Lepontine dome characterized by the following polyphase metamorphic evolution: (1) Subductionrelated syn-D1 (Safien phase) HP/LT metamorphism under blueschist facies conditions (350-400 °C and 1.2-1.4 GPa) was established at 42-40 Ma, as revealed by 40Ar/39Ar dating of white mica associated with Fe-Mg carpholite; the early high-pressure event was followed by “cold” isothermal (or cooling) decompression during D2 nappe-stacking (Ferrera phase) for which an age of 36-33 Ma is inferred based on 40 Ar/39Ar dating of white mica replacing Fe-Mg carpholite. (2) Early collision-related greenschist facies overprint (350-425 °C) post-dating substantial decompression and associated D2 deformation was established at 32-29 Ma and affected both HP and LP metasediments. This metamorphic event clearly predates D3 deformation (Domleschg phase, ~25 Ma) as is evidenced by folded isotemperature contours. (3) Collision-related Barrovian overprint (500-590 °C and 0.5-0.8 GPa) represents a second and considerably younger (post 20 Ma) “isobaric” heating pulse only preserved in the SW part of the investigated area. Hence amphibolite facies metamorphism representing the mature stage of a colliding orogen is clearly separated by D2 and D3 deformations, as well as by an intervening greenschist facies event, from the D1 high-pressure stage. Amphibolite facies overprint occurred before and/or during the initial stages of D4 (Chièra phase), representing a second nappe-refolding event. This investigation revealed a significant time gap in the order of some 20 Ma between subductionrelated HP/LT metamorphism and collision-related MP/MT Barrovian overprint. This supports the notion of a polymetamorphic evolution associated with a bimodal P-T path. The results of this study argue that heat release from radioactive decay of vast amounts of accreted continental-derived basement nappes may play an important role in contributing much to heat production needed for amphibolite facies Barrow-type overprint. Based on field evidence, we conclude that heat transfer in the north-eastern Lepontine was essentially conductive during the latest stages of the thermal evolution.

Present-day tectonic activity at the southern end of the Upper Rhine Graben in central Western Europe is evidenced by significant seismicity, which has been documented over hundreds of years. The hazard that is posed by this activity was violently demonstrated in 1356, when an earthquake with an estimated magnitude of ML≈6.5 caused extensive damage to the area of Basel in north-western Switzerland. A sound understanding of the regional tectonic deformation field is a prerequisite for the accurate assessment of this hazard. However, long-term deformation rates in this region are very low. Together with the presence of a network of fault families of different age and orientation, which results from the complex tectonic evolution of this area in the Neogene, this makes the characterisation of the regional deformation field and the identification of active faults difficult. Nevertheless, for a better comprehension of the active tectonic processes in general, and for the assessment of the seismic hazard in this region in particular, an improved understanding of the regional tectonic evolution in the recent geological past is indispensable. This thesis addresses the recent tectonic history of the Basel area by combining seismological data with an investigation of the geomorphological evidence of tectonic activity. The fact that tectonic activity can be recorded and preserved by the landscape provides an additional source of information that has been little used so far. It offers an opportunity to extend the time-scale of observation from the decades covered by (instrumental) seismologic and geodetic records further into the past. Whereas a wide range of geomorphic features can carry signatures of past tectonic events, the focus in this work is laid on fluvial geomorphology. The fluvial system in the northern Alpine foreland has been affected by a number of large-scale tectonic events since the late Oligocene. Apart from processes related to the Alpine orogeny and the rifting of the Upper Rhine Graben and Bresse Graben, the evolution of the Jura fold-and-thrust belt, the most external element of the Alpine orogen, dramatically influenced the drainage system. Sedimentary and morphological evidence of former river courses allow further constraining the evolution of the drainage system between the Oligocene and the Quaternary. The tectonic history in the Quaternary was studied using a quantitative geomorphological approach. On the basis of a digital elevation model, geomorphic indices (steepness and concavity index) were determined to characterise the longitudinal profile for a large number of rivers in the area of the southern Upper Rhine Graben and the eastern Jura fold-and-thrust belt. The spatial distribution of these indices indicates uplift of a region roughly corresponding to the Jura fold-and-thrust belt, as well as subsidence of the interior parts of the Upper Rhine Graben relative to the Tabular Jura. A morphological analysis of Late Quaternary alluvial terraces in the lower Aare valley, northern Switzerland, was carried out using a high-resolution digital elevation model. The results suggest regional northward tilt during the past 20’000 years, compatible with both a general (isostatic) uplift of the Swiss Molasse basin, and continuing convergence due to ongoing Alpine collision. The geomorphic data revealed no unambiguous evidence of recent tectonic activity on individual faults. Furthermore, no evidence of recent or ongoing thin-skinned deformation in the Mesozoic sedimentary cover could be identified. The study area at the junction of the Upper Rhine Graben and the Jura fold-and-thrust belt is characterised by a pronouncedly diffuse distribution of deformation, typical for regions where strain is accommodated on inherited tectonic structures. The superposition of large-scale regional uplift and small-scale deformation on individual faults, as well as seismic and aseismic movements, results in a distinct heterogeneity of deformation styles in the northern Alpine foreland.

This thesis was carried out within the framework of the international EUCOR-URGENT project and represents a joint study (co-tutelle) between the Universities of Basel and Besançon. It is devoted to the structural evolution and present-day tectonic activity of the region of Franche Comté in Eastern France, a region that is located at the intersection between the Jura fold-and-thrust belt representing the front of the Alpine orogen and the immediately adjacent northwestern foreland, characterized by the intra-continental Rhine-Bresse Transfer Zone (RBTZ). The formation of the RBTZ, that forms a central segment of the Paleogene European Cenozoic Rift System, involved the extensional reactivation of the Late Paleozoic Burgundy Trough System. Substantial extension occurred in Eo-Oligocene times and was achieved by ENE-WSW striking normal faults that are highly oblique to the dominant strike of the Rhine and Bresse grabens. Fission track data suggest that basement reactivation also contributed to the Eo-Oligocene exhumation of the Late Paleozoic La Serre Horst in the context of rifting. Basement reactivation in connection with the formation of the RBTZ resulted in complex fault patterns and local stress field perturbations, especially in the surroundings of the pre-existing Paleozoic horst structure. During Late Miocene to Early Pliocene times the northwestern most segment of the thin-skinned Jura fold-and-thrust belt, the Besançon Zone, encroached onto the RBTZ. Moreover, NW-SE directed foreland compression caused thick-skinned, transpressive reactivation of the RBTZ that started by Late Pliocene times at the earliest. Present-day seismicity in the RBTZ indicates that thick-skinned tectonics are still active and may reflect ongoing tectonic underplating in the northwestern Alpine foreland. Post-Pliocene relative rock uplift is recorded along the RBTZ by differential erosion of the Middle Pliocene Sundgau-Forêt de Chaux Gravels on a regional scale. Uplifted remnants of this gravel plain, identified by heavy mineral analyses, permitted to determine a latest Pliocene to recent minimum regional rock uplift rate of 0.05 +/- 0.02 mm/yr. A reconstruction of the Plio-Pleistocene drainage basin evolution of the Ognon and Doubs Rivers revealed that this relative rock uplift is still ongoing and most likely partly driven by the inversion of the RBTZ. Pleistocene folding near Besançon is evident from differentially up warped paleo-meanders along the Citadelle Anticline. This deformation is apparently enhanced by the bedrock incision of the Doubs River and associated with higher local uplift rates of 0.17 +/- 0.03 mm/yr. The results of this study vividly illustrate the dynamic processes that control the progressive evolution of continental collisional forelands. It appears that while the evolution of the RBTZ was largely controlled by the reactivation of pre-existing structures, its present tectonic activity is to some extent also controlled by surface processes and involves positive feedbacks between large-scale uplift, enhanced erosion and active deformation.

Combining thermochronological methods with structural field data, this study aims to reconstruct the Tertiary burial and exhumation history of the northeastern part of the Tisza‐ Dacia block during its invasion in the Carpathian embayment and final soft collision with the European margin. Zircon fission track data additionally provide information about the last metamorphic overprint during the Cretaceous. Within the basement units of the northern Central East Carpathians (Bucovinian nappe stack) and the Preluca massif (Biharia unit) zircon fission tracks are largely reset during the last (Cretaceous) orogeny. Temperatures during this Alpine metamorphic overprint increase from external to internal within the northern East Carpathians from sub‐greenschist facies conditions to at least greenschist facies conditions. Greenschist facies conditions are also observed in the Preluca massif. The close neighbourhood of Coniacian to Campanian zircon FT cooling ages with Cenomanian sediments suggests Late Cretaceous tectonic exhumation in the northern East Carpathians. The most likely explanation for this tectonic exhumation is a ‐ so far undocumented ‐ Late Cretaceous extension related to orogenic collapse (Gosau type basins). The Tertiary evolution is characterised by the invasion of the previously amalgamated Tisza‐Dacia and ALCAPA blocks into the Carpathian embayment and Miocene soft collision of both these blocks with the European margin. The juxtaposition of the ALCAPA and Tisza‐Dacia blocks, with Tisza‐Dacia in a lower plate position, is announced by the onset of Oligocene turbiditic sedimentation. The Burdigalian SE‐directed over‐thrusting of the Pienides (non‐ metamorphic flysch units) is interpreted to express the final stages of this juxtaposition. Burial heating caused full annealing of fission tracks in apatite (i.e. >120°C) in the Central East Carpathian basement in the NE of the study area, while in the basement of the Preluca massif in the SW of the study area temperatures related to Paleogene to Early Miocene burial did not exceed 80°C. The post‐Burdigalian (post‐16 Ma) soft collision of Tisza‐Dacia with the European margin occurred in two stages expressed by predominantly sinistral strike‐slip deformation during constant NE‐SW shortening. During and following soft collision, combined uplift and erosion caused exhumation of the buried rocks along the European margin. Uplift reaches up to 9 km in the Rodna horst The first post‐Burdigalian transpressional stage (16‐12 Ma) is related to perpendicular convergence of Tisza‐Dacia with the NW‐SE striking European margin. Minor exhumation during this stage resulted in Middle Miocene apatite fission track cooling ages (15‐13 Ma) in the west of the study area. The transtensional stage (12–10 Ma) led to the formation of the Bogdan‐Dragos‐Voda fault system. Sinistral transtension allowed for the docking and fitting of Tisza‐Dacia with the NW‐ SE striking European margin. Oblique E‐W convergence led to strain partitioning with thrusting in the external thrust belt and internal strike‐slip deformation. Differential lateral movements are distributed and deformation is accommodated by E‐W striking sinistral strike slip faults and SW‐NE striking normal faults, which led to fragmentation into SW‐tilted blocks. Fragmentation and differential offset along the bounding faults resulted in the formation of triangular‐shaped graben and corresponding horst structures. Enhanced exhumation during transtensional activity led to advective heat transport and resulted in Middle to Late Miocene apatite fission track cooling ages (13‐7) in the east of the study area.

Chapter 1: Apparent divergence of thrusting directions horth and south of the Pelvoux massif: implications for the evolution of the Western Alpine Arc: In the Western Alps, the Penninic Basal Contact (PBC, Ceriani et al. 2001) defines the tectonic boundary between the external Dauphinois domain and the interanl Penninic units. During the Eocene, the PBC corresponds to the suture between Dauphinois and Subriançonnais/Briançonnais domains related to the subduction of the Valais ocean (Ceriani et al. 2001). In the Oligo-Miocene, i.e. during a second and post-collisional stage, Eocene structures were passively transported towards the WNE along a major out-of-sequence thrust, the Roselend thrust (RT), partially coinciding with and reactivating the PBC. Structural analysis of key outcrops combined with microfabric investigations of calcyte ultramylonites allowed to trace the southern continuation of the RT in a broad shear zone at the rim of the Pelvoux massif and further south along the Briançonnais front (Tricart 1980) at the rear of the Embrunais Ubaye nappe stack. The RT finally branches into a sinistral strike slip zone NE of the Argentera massif. The area south of the Pelvoux massif is additionally characterized by SW-directed thrusting, a feature totally absent north of it. Detailed investigations of outcrops found along strike of the RT, the basal decollement of both Dauphinois para-autochthonous Tertiary cover and Helmenthoid Flysch of the Embrunais Ubaye nappe stack reveal that top-SW thrusting is a younger (i.e. D2) event, overprinting earlier features linked to D1 WNW-directed displacements. The youngest deformation event found in the area (D3) is consistent with normal faulting along the Durance system. On a larger scale, it is concluded that the whole Adriatic indenter was thrusted onto the European plate along the RT during Oligo-Miocene times. Activity along this structure is linked to dextral movements along the Rhone-Simplon line and sinistral movements at the rear of the Argentera massif. Additionally, it is proposed that the onset of D3 SW-directed movements finds its origin in the opening of the western Mediterranean basin and the foramtion of the Appenine chain in middle Miocene times. Chapter 2: Microfabrics of calcite ultramylonites recording coaxial and non-coaxial deformation kinematics: examples from the Rocher de l'Yret shear zone (Western Alps): Microfabrics were analysed in calcite mylonites from the rim of the Pelvoux massif (Western Alps, France). WNW-directed emplacement of the internal Penninic units onto the Dauphinois domain has lead to intense deformation of an Eocene-age nummulitic limestone under lower anchizone metamorphic conditions (slightly below 300°C). Two types of microfabrics developed during deformation under coaxial or non-coaxial kinematics, respectively, primarily by dislocation creep accompanied by dynamic recrystallization in the absence of twinning. Coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry. Their texture is characterized by two c-axis maxima at the periphery of the pole figure, symmetrically oriented at 15° from the normal to the macroscopic foliation. Non-coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterized by a single oblique c-axis maximum tilted with the sense of shear by about 15°. From the analysis of suitably oriented slip systems for the main texture components under given kinematics it is inferred that the orthorhombic textures developed in coaxial kinematics fabour activity of and slip along the f- and r-planes, respectively, with minor contributions of basal slip. In contrast, the monoclinic textures developed during simple shear are most suited for duplex slip along the basal plane. The transition between orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallization upon texture development. Calcite textures alone should not be used as unequivocal shear sense indicators, but need to be complemented by microstructural criteria such as shape preferred orientations, grain size estimates and amount of twinning. Chatper 3: Microfabric analysis of calcitic marbles from the area investigated in the Western Alps and the Gavernie basal contact (Central Pyrenees): In the previous chapter, a model of microfabric evolution of calcite ultramylonites, plastically deformed at temperatures lower than 350°C, has been presented. The very specific setting of the outcrop investigated in great details at the "Rocher de l'Yret" shear zone (RYSZ) allowed for the recognition of both coaxial and non-coaxial deformation kinematics. The samples deformed with a dominant component of rotational deformation show a c-axis distribution tilted synthetically with the sense of shear. In the absence of twinning, this feature, commonly observed for quartz tectonites, can be used as a reliable shear sense indicator. Additionally, the model allows for the recognition of incipient rotational deformation in the bulk flow accommodated in the rock. The structural data presented in chapter 1 will now be completed by means of a microfabric analysis of a series of calcitic marbles, found in abundance in the investigated area. The results of investigations on calcite ultramylonites found along the Roselend Thrust (RT) are presented first. four localities along the RT have been investigated between the eastern rim of the Pelvoux massif in the North and the rear of the Argntera massif in the South (sites BFY, Laux, Reot and Arg in fig 3.1). This study aims to 1) independently confirm the overall WNW-directed sense of transport along the RT, 2) deduce the type of strain along this structure and its possible variations using the model of microfabric evolution presented in chapter 2. In a second step, the basal decollement of the Dauphinois parautochthonous cover from the southeastern rim of the Pelvoux massif will be investigated. Such decollement occurred within the nummulitic limestone layer intensively mylonitised in the Dormillouse valley (site Dorm, see fig. 3.1 and 3.2). This study confirms the overall top-SW overprinting deformation recorded in this domain and documents important bulk flow partionning within the basal decollement level of the Eocene stratigrahpic series. Finally the restults of investigations on samples from the Gavernie thrust from the central Pyrenees (courtesy J.H.P. de Bresser) will be presented (see fig. 3.37). The restults are in accordance with the overall top-S directed emplacement of the Gavernie nappe during Pyrenean orogeny and give evidence for strain variations within the shear zone developed along the Gavarnie basal thrust., pas de résumé

In the Rio Tinguiririca valley in the Main Cordillera of the Andes of central Chile, 35 ° south, parts of a stratigraphic section ranging from the late Jurassic to the Quaternary are exposed. Fission track analysis was carried out on samples from all the stratigraphic units exposed in the area in order to gain information on the low–grade metamorphic history of the Central Andes and to test older models for the metamorphic and tectonic evolution of the area. The sequence exposed in the Rio Tinguiririca valley is characterised by several distinctive features not found in other localities in the Central Andes; the deposits of the middle Cretaceous (Aptian – Albian) Colimapu Formation and of the middle to late Micoene Farellones Formation are completely missing in the study area. Instead, a volcanic tuff layer, the White Tuff, and a unit consisting of fan deposits and alluvial plane deposits, the Brownish–Red Clastic Unit, unconformably overlie the Late Jurassic deposits of the Ba˜nos del Flaco Formation. The fission track data give some indications on the style and timing of metamorphic events in the study area, enable more accurate constraint of the age of the Brownish–Red Clastic Unit and allow some statements on the tectonic evolution of the study area from the Late Jurassic to present. Burial metamorphism has been proposed by various authors as the main mechanism to produce large suites of rocks altered at low grades in the Central Andes. The results of this study indicate that, on the contrary, hydrothermal alteration connected to magmatic and/or volcanic activity was the main cause of alteration of the rocks and that burial metamorphism played at most a very minor role. Pulses of hydrothermal activity appear to have occurred from Cretaceous to almost recent times and led to alteration of the rocks at slightly varying metamorphic conditions at different times in different parts of the study area. A new model is proposed for the tectonic evolution of the study area. Fission track analysis of detrital zircons from the Brownish–Red Clastic Unit shows that the unit must have been deposited during the latest Cretaceous (Maastrichtian) and that it is certainly younger than the White Tuff. Thermal modelling shows that considerable exhumation of the lower part of the Rio Damas Formation occurred during the Late Cretaceous to Early Tertiary. This exhumation is thought to be connected to tilting and erosion of the Mesozoic units in the area prior to the formation of an extensional basin in the Late Eocene. Data from the Eocene to Miocene Coya Machali Formation imply that sedimentation within the Tertiary basin continued somewhat longer than hitherto supposed.