Periadriatic Research Articles

Orogenic structure of the Eastern Alps, Europe, from TRANSALP deep seismic reflection profiling

The TRANSALP Group, comprising of partner institutions from Italy, Austria and Germany, acquired data on a 340 km long deep seismic reflection line crossing the Eastern Alps between Munich and Venice. Although the field work was split into four campaigns, between fall 1998 and summer 2001, the project gathered for the first time a continuous profile across the Alps using consistent field acquisition and data processing parameters. These sections span the orogen itself, at its broadest width, as well as the editor Fred Davey and the two adjacent basins. Vibroseis and explosion data, complementary in their depth penetration and resolution characteristics, were obtained along with wide-angle and teleseismic data. The profile shows a bi-vergent asymmetric structure of the crust beneath the Alpine axis which reaches a maximum thickness of 55 km, and 80–100 km long transcrustal ramps, the southward dipping ‘Sub-Tauern-Ramp’ and the northward-dipping ‘Sub-Dolomites-Ramp’. Strongly reflective patterns of these ramps can be traced towards the north to the Inn Valley and towards the south to the Valsugana thrust belt, both of which show enhanced seismicity in the brittle upper crust. The seismic sections do not reveal any direct evidence for the presence of the Periadriatic Fault system, the presumed equivalent to the Insubric Line in the Western Alps. According to our new evolutionary model, the Sub-Tauern-Ramp is linked at depth with remnants of the subducted Penninic Ocean. The ‘crocodile’-type model describes an upper/lower crustal decoupling and wedging of both the European and the Adriatic–African continents.

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 μm). 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 μm were: (1) 5.2±2.6 Ma (2 σ) 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.

Contemporaneous plutonism and strike‐slip faulting: A case study from the Tonale fault zone north of the Adamello pluton (Italian Alps)

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.

Shear zones and magma ascent: A model based on a review of the Tertiary magmatism in the Alps

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.

The Smrekovec Tertiary and related volcanism (Slovenia): sedimentology, geochemistry and tectonic evolution

The Smrekovec Tertiary (Slovenia) represented an important marine connection between the Tethys Ocean and the developing Paratethys. The Paleogene sequence rests unconformably on Permotriassic rocks of the Southalpine Kamnik Alps. It starts with Eocene terrigenous sediments and marine carbonates grading into Oligocene shallow marine sediments. After an increasing deepening of the environment, explosive eruptions of the Smrekovec volcano to the N led to the deposition of thick volcaniclastics. The calc-alkaline volcanic rocks and their associated volcaniclastics are of andesitic to (rhyo)dacitic composition. Volcanic activity lasted from Rupelian until Chattian (if not earliest Miocene) times. The present appearance of the Smrekovec Tertiary is interpreted to result from late-Alpine tectonics along the Periadriatic Fault possibly representing a pull-apart or extensional duplex structure within the Permotriassic succession of the Kamnik Alps. It is thus an erosional remnant of a former larger depositional area and did not have the form of the present basin around Smrekovec in Paleogene times.

Present‐day lithospheric strength of the Eastern Alps and its relationship to neotectonics

We calculate the present‐day lithospheric strength of the Eastern Alps along the new reflection seismic profile TRANSALP to examine vertical and lateral strength variations and their implications on neotectonic activity of the Eastern Alps. The large‐scale geometry of the Eastern Alps and the spatial distribution of upper, and lower crustal layers, and the lithospheric mantle is constrained by the deep seismic line. Two rheological models, coupled to a kinematic thermal model that accounts for the thermal evolution of the Eastern Alps for the last 30 Myr, are investigated for the present‐day lithospheric configuration in the Eastern Alps. Models with strong (Model A) and weak (Model B) crustal rheologies predict the European and the Adriatic plates to be stronger than the central zone of the orogen comprising the region between the Inntal Fault and the Periadriatic Fault. Model A is characterized by a brittle‐ductile boundary between 14 and 9 km depth and strong coupling of the mechanically strong lower crust to the upper mantle, whereas Model B suggests the presence of a thick decoupling zone between the upper crust and the upper mantle and a shallower brittle‐ductile boundary (7–10 km). Of these end‐member scenarios, Model A is in better agreement with neotectonic data including seismicity down to the upper‐lower crust boundary within the Adriatic plate, uplift of the central zone of the Eastern Alps and the Southern Alps, and eastward escape of fault‐bound blocks. Such deformation pattern is best explained by lateral extrusion upon north‐south compression supporting a strong‐weak‐strong configuration of tectonic units along the TRANSALP line.

Detrital Fission-Track Analysis and Sedimentary Petrofacies as Keys of Alpine Exhumation: The Example of the Venetian Foreland (European Southern Alps, Italy)

Sedimentary petrography and detrital apatite fission-track analysis of sediments from the Oligo-Miocene Venetian foreland succession (NE Italy) reveal a multi-stage evolution of the Alpine source areas. During the first stage of sedimentation (Chattian to Langhian), the foreland basin was filled by sediments derived from erosion of mainly crystalline Austroalpine units exhumed north of the Periadriatic Lineament. These sediments are characterized by litharenites with mean quartz content of about 61% and by a mean detrital apatite fission-track peak of about 30 Ma. The Permian-Paleogene sedimentary cover of the Southalpine crystalline basement (Dolomite region) was bypassed by the sediments and made only a minor input. From the Serravallian onwards, the foreland basin was incorporated into the Southalpine thrust belt. The compressional events of the Valsugana phase resulted in thrusting and uplift of the Southalpine domain, as documented by Tortonian fission-track ages in the hanging wall of the major regional thrust (Valsugana thrust fault). The Southalpine crystalline basement, unaffected by Alpine metamorphism, and its sedimentary cover became the main source of sediments, as revealed by the increase in extrabasinal carbonate grains and detrital apatite grains with Late Triassic-Jurassic fission-track ages. During this final stage of basin evolution, about 3000 m of sediments were deposited. These strata subsequently have been uplifted and eroded since the Pliocene, indicating a southward migration of the Alpine deformation front.

The continuation of the Internal Dinaridic units in the area between the Periadriatic Lineament and the Southern Alps in Slovenia

Three Internal Dinaridic tectonostratigraphic units are included in the PANCARDI domain; 1) the Bosnian Flysch, composed of the Liassic to Berriasian Vranduk Subgroup and the Albian to Maastrichtian Ugar Subgroup, originating on the passive Tethyan margin, 2) the Dinaride Ophiolite Zone, made up of the Radiolarite Formation, ophiolite included within the Jurassic olistostrome mélange, and a Cretaceous overstep sequence, partly with Urgon-type(?) signatures, and 3) the Sava-Vardar Zone, composed of Cretaceous-Early Paleogene flysch, locally with subduction-related basalt-rhyolites, a Paleogene, very low to medium-grade metamorphic sequence originating from the Cretaceous-Paleogene flysch, Paleogene tectonized ophiolite mélange, Eocene syncollisional granitoid occurrences and Oligocene postcollisional ones, accompanied by coeval shoshonite and andesite. All these formations occur as allochthonous blocks within two segments of the southern and western Pannonian Basin. 1) In the adjoining Tisia-Dinarides segment, the Sava-Vardar Zone lithologies occur both at the surface and in the subsurface of the Pannonian Basin, as the result of postorogenic Dinarides-Tisia interaction. Those located in the basement were uplifted during the Oligocene wrench faulting, which controlled the initial development of the Sava and Drava depressions. Those found at the surface were emplaced during the Pliocene phase of strike-slip faulting. 2) More common are Internal Dinaridic fragments sandwiched within the Alps-Dinarides-Tisia (e.g. Carpathians) triple junction area, e.g. the Zagorje-Bükk-Meliata Zone. In its southwestern Sava Subzone occur fragments of the Bosnian Flysch Zone and Sava-Vardar Zone, represented by a Paleogene tectonized ophiolite mélange, Cretaceous-Paleogene flysch and postcollisional andesite-shoshonite. The northeastern Bükk-Meliata Subzone is composed of a Jurassic ophiolite mélange correlative to the Dinaride Ophiolite Zone, which in its Slovakian part is thrust by Triassic, mainly carbonate formations. The accompanying Mónosbél Flysch can be correlated with the Vranduk Subgroup of the Bosnian Flysch. The displacement of the Internal Dinaridic formations can only partly be explained by Tertiary escape (extrusion) tectonics.

Outline of the geology of Slovenia

Taking into consideration the Alps/Dinarides connection, the western part of the Zagorje-Mid-Transdanubian (or Sava) Zone (ZMTZ) in Slovenia, which is located between the Eastern and Southern Alps, includes disconnected outcrops of the northwesternmost Internal Dinaridic units. The northern part of the ZMTZ in Slovenia, which is close to the Periadriatic Lineament, is mainly composed of an Albian-Cenomanian to Late Cretaceous flysch sequence, underlain by Jurassic basinal sediments, which can be correlated to the Sava-Vardar Flysch. The outcrops are located in frontal parts of the Julian-Savinja Nappe. The southern part of the ZMTZ in Slovenia includes the Sava Nappe (or the Slovenian Trough), which is thrust upon the northern margin of the Adriatic-Dinaridic carbonate platform, e.g. the External Dinarides and Southern Alps, respectively. It is composed of Aptian to Cenomanian clastics and carbonates, disconformably overlain by Late Cretaceous carbonate flysch. It can be correlated to the Bosnian Fysch in the Central Dinarides. Both the Northern and Southern Zones can be followed westward up to Italian frontier. All presented data indicate a spatial connection between the northwesternmost Dinarides and the easternmost Alps during Alpine geodynamic evolution. Their apparent lack of connection in the present structure of the Dinarides and Alps is the result of the postorogenic indenting of Adria or of the African promontory, and related strike-slip faulting.

The Palaeogene forearc basin of the Eastern Alps and Western Carpathians: subduction erosion and basin evolution

Scarce Palaeogene sediment remnants in the Eastern Alps and Western Carpathians are interpreted as remains of a continuous forearc basin. New apatite fission-track geochronological data corroborate mild Paleocene–Eocene exhumation and relief formation in the Eastern Alps. Palinspastic restoration and nine palaeogeographical maps of the Eastern Alps and Western Carpathians ranging from the Paleocene to the Late Oligocene epoch illustrate west to east migration of subsidence in the forearc basin. Subsidence isochrons indicate that oblique subduction of the European plate below the Adriatic plate was responsible for forearc basin migration at a rate of 8 mm a −1 . The Periadriatic Lineament was formed as a result of shearing by oblique subduction. The Neogene to recent Sumatra forearc basin is an analogue for the evolution of the East Alpine–West Carpathian forearc basin.

The Pejo fault system: An example of multiple tectonic activity in the Italian Eastern Alps

Research Article| May 01, 2003 The Pejo fault system: An example of multiple tectonic activity in the Italian Eastern Alps Giulio Viola; Giulio Viola 1Department of Geological Sciences, University of Cape Town, 7701 Rondebosch, South Africa Search for other works by this author on: GSW Google Scholar Neil S. Mancktelow; Neil S. Mancktelow 2Department of Earth Sciences, ETH, Sonneggstrasse 5, 8092 Zürich, Switzerland Search for other works by this author on: GSW Google Scholar Diane Seward; Diane Seward 2Department of Earth Sciences, ETH, Sonneggstrasse 5, 8092 Zürich, Switzerland Search for other works by this author on: GSW Google Scholar Andreas Meier; Andreas Meier 2Department of Earth Sciences, ETH, Sonneggstrasse 5, 8092 Zürich, Switzerland Search for other works by this author on: GSW Google Scholar Silvana Martin Silvana Martin 3Dipartimento di Scienze Chimiche, Fisiche e Matematiche, Università dell'Insubria, via Valleggio 11, 22100 Como, Italy Search for other works by this author on: GSW Google Scholar Author and Article Information Giulio Viola 1Department of Geological Sciences, University of Cape Town, 7701 Rondebosch, South Africa Neil S. Mancktelow 2Department of Earth Sciences, ETH, Sonneggstrasse 5, 8092 Zürich, Switzerland Diane Seward 2Department of Earth Sciences, ETH, Sonneggstrasse 5, 8092 Zürich, Switzerland Andreas Meier 2Department of Earth Sciences, ETH, Sonneggstrasse 5, 8092 Zürich, Switzerland Silvana Martin 3Dipartimento di Scienze Chimiche, Fisiche e Matematiche, Università dell'Insubria, via Valleggio 11, 22100 Como, Italy Publisher: Geological Society of America Received: 13 Dec 2001 Revision Received: 16 Oct 2002 Accepted: 04 Nov 2002 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (5): 515–532. https://doi.org/10.1130/0016-7606(2003)115<0515:TPFSAE>2.0.CO;2 Article history Received: 13 Dec 2001 Revision Received: 16 Oct 2002 Accepted: 04 Nov 2002 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Giulio Viola, Neil S. Mancktelow, Diane Seward, Andreas Meier, Silvana Martin; The Pejo fault system: An example of multiple tectonic activity in the Italian Eastern Alps. GSA Bulletin 2003;; 115 (5): 515–532. doi: https://doi.org/10.1130/0016-7606(2003)115<0515:TPFSAE>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Pejo fault in the Italian Eastern Alps is a major sinistral transtensional fault. It marks the boundary between basement units displaying contrasting thermal histories, with Alpine (i.e., Mesozoic–Cenozoic) cooling ages preserved in the footwall juxtaposed against Variscan (i.e., Carboniferous– Permian) age in the hanging wall. Structural investigations, together with fission-track analysis, confirm a Late Cretaceous age for the Pejo fault, which excludes any direct kinematic contribution of the Pejo fault to the late Oligocene–Neogene evolution of the central-eastern segment of the Periadriatic fault. However, our results establish the importance of a major early Oligocene north-south to north-northwest–south-southeast shortening phase in the Central-Eastern Alps, which resulted in the development of new reverse shear zones, in the reactivation of the Pejo fault with a reverse motion, and in regionally important folding. The Pejo mylonites are folded on a kilometer scale around an east-northeast–trending axis. Field observations and fission-track analysis suggest a post-Oligocene age for the folding phase. Apatite fission-track data in the Pejo valley area reveal the base of a fossil apatite partial annealing zone exhumed to the surface. This finding argues for >4 km of exhumation since the Miocene, which was related to a major pulse of exhumation that began at ca. 15 Ma. This study suggests that the simple distinction between largely pre-Alpine fabrics of Variscan age in the hanging wall of the Pejo fault (Tonale nappe) and Alpine fabrics (Cretaceous) in the footwall (Campo-Ortler nappe) is not universally valid. Alpine overprinting is confined to the mylonitic shear zone itself. Deeper into the footwall, pre-Alpine structures are still well preserved. Earlier maps and interpretations based on a clear distinction between Tonale and Campo should be viewed with caution. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Thermal modeling of Carboniferous to Triassic sediments of the Karawanken Range (Southern Alps) as a tool for paleogeographic reconstructions in the Alpine–Dinaridic–Pannonian realm

Vitrinite reflectance was measured in Late Carboniferous to Triassic shales, siltstones and marls of the Karawanken Range. Thermal models of the central South-Karawanken Range were calibrated on the basis of these data. They suggest an eroded overburden of more than 3,200 m of Jurassic to Cretaceous sediments and a heat flow in the range of 42 to 60 mW m−2 during the time of maximum subsidence. Because the reconstructed thermal history of the South-Karawanken Range is very similar to the thermal history of the Generoso basin (western Southern Alps), these data provide strong evidence for a deep basinal position of the Southern Karawanken Range during Jurassic to Cretaceous times. A vitrinite reflectance anomaly at the northern margin of the South-Karawanken Range is explained by advective heat transport during the Oligocene. The heat source for the anomalies at the western margin of the Seeberg Rise and in the area between the Periadriatic Lineament and the Donat Fault Zone is unknown. Vitrinite reflectance in Late Triassic sediments indicates the South-Karawanken Range and the South-Zala Unit of the Pannonian basement as exotic blocks in the Sava Composite Unit. This is explained by Miocene displacement of structural units, which were derived from different paleogeographical segments of the Permo-Mesozoic western Tethyan margin.

Tectonic contact beetwen Paleozoic and Triassic rocks south of Podolševa (Slovenia)

Tectonic contact between Paleozoic and Triassic rocks south of Podolseva, which passes prominent cliffs over the left bank of Savinja river (Klemenca pec, Jamnikova pec, Golerjeva pec, Strevceva pec and Huda pec), is on the basis of the new mapping a steep fault, dipping to the north. In the last phase, the fault was dextral strike - slip active, before was probably reverse, and can represent accompanying structure of Periadriatic lineament. It was under transpresive tectonic regime and complies with model of positive flower structure. We named it Podolsevski prelom (Podolseva fault).

Paleogene igneous activity along the easternmost segment of the Periadriatic-Balaton Lineament

In the Pannonian Basin three Paleogene igneous regions can be outlined, namely the Zala Basin Shear Zone, the Velence Mts and the Recsk Region. These igneous regions are aligned along the easternmost Periadriatic-Balaton Lineament System. The igneous bodies are built up mostly by effusive rocks (andesite, dacite and basaltic andesite); however, intrusive rocks (tonalite, diorite) have been identified as well. The radiometric age of the effusive and intrusive rocks is scattered around 30 Ma, which falls into the range of the igneous bodies aligned along the Periadriatic Line (Bergell, Adamello, Riesenferner, Karawanke, etc.). Nevertheless, an Eocene onset of the magmatic activity in the Pannonian Basin is accepted on the basis of biostratigraphic data. As major and trace element composition range of the Paleogene igneous suites in the Pannonian Basin are basically the same, they are thought to have undergone the same pre-crystallization history. Geochemical characteristics of these calc-alkaline igneous r...

Dating fault-generated pseudotachylytes: comparison of 40Ar/39Ar stepwise-heating, laser-ablation and Rb–Sr microsampling analyses

Three different geochronological techniques (stepwise-heating, laser-ablation 40Ar/39Ar, Rb–Sr microsampling) have been evaluated for dating fault-generated pseudotachylytes sampled along the Periadriatic Fault System (PAF) of the Alps. Because pseudotachylytes are whole-rock systems composed of melt, clast and alteration phases, chemical control from both Ar isotopes (Cl/K, Ca/K ratios) and EMPA analyses is crucial for their discrimination. When applied to stepwise-heating 40Ar/39Ar analyses, this approach yields accurate melt-related ages, even for complex age spectra. The spatial resolution of laser-ablation 40Ar/39Ar analyses is capable of contrasting melt, clast and alteration phases in situ, provided the clasts are not too fine grained, the latter of which results in integrated mixed ages without geological information. Elevated Cl/K and Ca/K ratios were found to be an invaluable indicator for the presence of clast admixture or inherited 40Ar. Due to incomplete isotopic resetting during frictional melting, Rb–Sr microsampling dating did not furnish geologically meaningful ages. On the basis of isotopic disequilibria among pseudotachylyte matrix phases, and independent Rb–Sr microsampling dating of cogenetic (ultra)mylonites, the concordant 40Ar/39Ar pseudotachylyte ages are interpreted as formation ages. The investigated pseudotachylytes altogether reveal a Cretaceous to Miocene history for the entire PAF, consistent with independent geological evidence. Individual faults, however, consistently reveal narrower intervals of enhanced activity lasting a few million years. Electronic supplementary material to this paper can be obtained by using the Springer LINK server at http://dx.doi.org/10.1008/s00410-002-0381-6

Origin and geodynamic evolution of Late Paleogene magmatic associations along the Periadriatic-Sava-Vardar magmatic belt

Along the Periadriatic Lineament in the Alps and the Sava-Vardar Zone of the Dinarides and Hellenides, Paleogene magmatic associations form a continuous belt, about 1700 km long. The following magmatic associations occur: (1) Eocene granitoids; (2) Oligocene granitoids including tonalites; (3) Oligocene shoshonite and calc-alkaline volcanics with lamprophyres; (4) Egerian-Eggenburgian (Chattian) calc-alkaline volcanics and granitoids. All of these magmatic associations are constrained by radiometric ages, which indicate that the magmatic activity was mainly restricted to the time span between 55 and 29 Ma. These igneous rocks form, both at surface and in the subsurface, the distinct linear Periadriatic-Sava-Vardar magmatic belt, with three strikes that are controlled by the indentation of Apulia and Moesia and accompanying strike-slip faulting. The geology, seismicity, seismic tomography and magnetic anomalies within this belt suggest that it has been generated in the African-Eurasian suture zone. Based on published analytical data, the petrology, major and trace element contents and Sr, Nd and O isotopie composition of each magmatic association are briefly defined. These data show that Eocene and Oligocene magmatic associations of the Late Paleogene Periadriatic-Sava-Vardar magmatic belt originated along a consuming plate margin. Based on isotopie systems, two main rock groups can be distinguished: (1) 87Sr/86Sr = 0.7036–0.7080 and δ18O = 5.9–7.2‰, indicating basaltic partial melts derived from a continental mantle-lithosphere, and (2) 87Sr/86Sr = 0.7090–72131 and δ18O = 7.3–11.5‰, indicating crustal assimilation and melting. The mantle sources for the primary basalt melts are metasomatized garnet peridotites and/or spinel lherzolites and phlogopite lherzolites of upper mantle wedge origin. The geodynamic evolution of the plutonic and volcanic associations of the Periadriatic-Sava-Vardar magmatic belt was related to the Africa-Eurasia suture zone that was dominated by break-off of the subducted lithospheric slab of Mesozoic oceanic crust, at depths of 90–100 km. This is indicated by their contemporaneity along the 1700 km long belt. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Origin and geodynamic evolution of Late Paleogene magmatic associations along the Periadriatic–Sava–Vardar magmatic belt

Along the Periadriatic Lineament in the Alps and the Sava–Vardar Zone of the Dinarides and Hellenides, Paleogene magmatic associations form a continuous belt, about 1700 km long. The following magmatic associations occur: (1) Eocene granitoids; (2) Oligocene granitoids including tonalites; (3) Oligocene shoshonite and calc-alkaline volcanics with lamprophyres; (4) Egerian–Eggenburgian (Chattian) calc-alkaline volcanics and granitoids. All of these magmatic associations are constrained by radiometric ages, which indicate that the magmatic activity was mainly restricted to the time span between 55 and 29 Ma. These igneous rocks form, both at surface and in the subsurface, the distinct linear Periadriatic–Sava–Vardar magmatic belt, with three strikes that are controlled by the indentation of Apulia and Moesia and accompanying strike-slip faulting. The geology, seismicity, seismic tomography and magnetic anomalies within this belt suggest that it has been generated in the African–Eurasian suture zone. Based on published analytical data, the petrology, major and trace element contents and Sr, Nd and O isotopic composition of each magmatic association are briefly defined. These data show that Eocene and Oligocene magmatic associations of the Late Paleogene Periadriatic–Sava–Vardar magmatic belt originated along a consuming plate margin. Based on isotopic systems, two main rock groups can be distinguished: (1) 87Sr/ 86Sr = 0.7036–0.7080 and δ 18O = 5.9–7.2‰, indicating basaltic partial melts derived from a continental mantle–lithosphere, and (2) 87Sr/ 86Sr = 0.7090–72131 and δ 18O = 7.3–11.5‰, indicating crustal assimilation and melting. The mantle sources for the primary basalt melts are metasomatized garnet peridotites and/or spinel lherzolites and phlogopite lherzolites of upper mantle wedge origin. The geodynamic evolution of the plutonic and volcanic associations of the Periadriatic–Sava–Vardar magmatic belt was related to the Africa–Eurasia suture zone that was dominated by break-off of the subducted lithospheric slab of Mesozoic oceanic crust, at depths of 90–100 km. This is indicated by their contemporaneity along the 1700 km long belt.

The eastern Tonale fault zone: a ‘natural laboratory’ for crystal plastic deformation of quartz over a temperature range from 250 to 700 °C

Near the eastern end of the Tonale fault zone, a segment of the Periadriatic fault system in the Italian Alps, the Adamello intrusion produced a syn-kinematic contact aureole. A temperature gradient from ∼250 to ∼700 °C was determined across the Tonale fault zone using critical syn-kinematic mineral assemblages from the metasedimentary host rocks surrounding deformed quartz veins. Deformed quartz veins sampled along this temperature gradient display a transition from cataclasites to mylonites (frictional–viscous transition) at 280±30 °C. Within the mylonites, zones characterized by different dynamic recrystallization mechanisms were defined: Bulging recrystallization (BLG) was dominant between ∼280 and ∼400 °C, subgrain rotation recrystallization (SGR) in the ∼400–500 °C interval, and the transition to dominant grain boundary migration recrystallization (GBM) occurred at ∼500 °C. The microstructures associated with the three recrystallization mechanisms and the transitions between them can be correlated with experimentally derived dislocation creep regimes. Bulk texture X-ray goniometry and computer-automated analysis of preferred [c]-axis orientations of porphyroclasts and recrystallized grains are used to quantify textural differences that correspond to the observed microstructural changes. Within the BLG- and SGR zones, porphyroclasts show predominantly single [c]-axis maxima. At the transition from the SGR- to the GBM zone, the texture of recrystallized grains indicates a change from [c]-axis girdles, diagnostic of multiple slip systems, to a single maximum in Y. Within the GBM zone, above 630±30 °C, the textures also include submaxima, which are indicative of combined basal 〈a〉- and prism [c] slip.

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.

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.