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-İzmir-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.
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•Tectonic map correlates tectonic units between Alps and western Turkey.•Profiles visualize architecture of Alpine-eastern Mediterranean orogens.•Review provides overview of Alpine-type orogens across national boundaries.
Common extrusion‐type models for the high‐ to ultrahigh‐pressure Adula nappe require a major normal fault along the top of this unit which is not conveyed in the structural record. This implies that ...such a normal fault existed but was completely erased during later deformational stages. However, there is evidence that decompression occurred during top‐to‐the‐foreland thrusting. We performed a new, purely structural kinematic restoration of the central part of the NFP20‐East cross section in order to estimate the burial depths of individual units without converting petrological pressure data into depth under the assumption that pressures were lithostatic. The results show that pressures within most of the units were close to but somewhat higher than lithostatic for several stages of the tectono‐metamorphic history. Only for the maximum burial stage of the Adula nappe, we estimate local tectonic overpressures of 40 to 80% of the lithostatic pressures. Accepting such an amount of overpressure, which is moderate compared to values theoretically possible, the Adula nappe was probably not subducted to subcrustal depth. We propose that the structural record of the Penninic nappe stack is quite complete and suggest that the decay of tectonic overpressure is a feasible explanation for decompression from eclogite‐ to amphibolite‐facies conditions during thrusting. Consequently, exhumation and convergence rates of the Eocene to Oligocene Alps may be smaller than previously assumed.
Key Points
Kinematics of Eastern Penninic Alps is reconstructed by structural record only
Tectonic overpressure solves conflict between structural and metamorphic record
Local and transient overpressure may determine P‐T‐t record of Adula (U)HP rocks
With ongoing Alpine convergence and deformation during exhumation there is a general progression from ductile to brittle behaviour on the Periadriatic Fault and kinematically related faults farther ...north (e.g. the Simplon–Rhone Fault and a diffuse, discontinuous zone of generally dextral strike–slip movement on the southern boundary of the Aar massif). K–Ar dating of fine grained illite from clay fault gouges provides a reliable method for establishing the maximum age of this transition to brittle faulting and, for short-lived faults, the approximate time of faulting itself. The new results establish that brittle faulting on the northeastern segment of the Canavese Fault (i.e. the part of the Periadriatic Fault southwest of Lago Maggiore) occurred around 20Ma, with south-side-up kinematics. A K–Ar age of ca. 17Ma for the crosscutting Giudicarie Fault in the Eastern Alps is effectively identical with an already published pseudotachylyte age and places a lower limit on major and continuous strike slip movements of the Periadriatic Fault. The age of brittle faulting farther north, on the southern border of the Aar Massif, is from 13.6±0.3 to 8.3±1.1Ma, consistent with the younger cooling and exhumation in this area. The dominantly dextral brittle faulting becoming younger to the north reflects the continued indentation and anticlockwise rotation of Adria as Alpine units become exhumed and progressively welded to the southern block. In contrast to the Eastern Alps, there is no field evidence for (westward) lateral extrusion of Alpine units relative to Adria and the European foreland.
► K–Ar illite dating of Neoalpine fault activity. ► Canavese Fault had a south-side-up kinematics in the Aquitanian. ► Brittle dextral faulting in the Aar Massif from ca. 13.5Ma on. ► Lateral extrusion model cannot explain orogen-parallel faults in the Western Alps.
The Dinaric–Hellenic mountain belt bends where two fault systems transect the orogen: (1) the dextral Shkoder-Peja Transfer Zone (SPTZ), active sometime between the Late Cretaceous and middle Eocene; ...(2) the Shkoder-Peja Normal Fault (SPNF), which accommodated NW–SE directed orogen-parallel extension. The SPTZ dextrally offsets the Dinaric–Hellenic nappes by ~ 75 km, a displacement attributed to reactivation of an Early Mesozoic rift transfer zone in the Adriatic margin during Paleogene subduction of the Pindos Ocean. This subduction involved an initial counter-clockwise rotation of the Hellenides with respect to the Dinarides around a pole at the NW end of the Budva–Krasta–Cukali–Pindos Basin. The SPNF overprints the SPTZ and is a composite structure comprising five fault segments: four of them (Cukali–Tropoja, Decani, Rožaje, Istog) were active under ductile-to-brittle conditions. They downthrow the West Vardar Ophiolite in the hanging wall. The Cukali–Tropoja and Decani segments exhume domes with anchizonal-to-greenschist-facies metamorphism in their footwalls. These structures formed during a first-phase of extension and clockwise rotation, whose Paleocene age is constrained by cross-cutting relationships. A second extensional phase was accommodated mainly by the fifth (Dukagjini) segment of the SPNF, a subsurface normal fault bordering syn-rift, mid-late Miocene clastic and lacustrine sediments in the Dukagjini Basin (DB) that are sealed by Plio-Pleistocene strata. This later phase involved subsidence of Neogene basins at the Dinaric–Hellenic junction coupled with accelerated clockwise oroclinal bending. The driving force for clockwise rotation is thought to be bending and rollback of the untorn part of the Adriatic slab beneath the Hellenides.
Continent-derived tectonic units in the Tauern Window of the Alps exhibit stratigraphic and structural traces of extension of continental margins eventually leading to the opening of the Alpine ...Tethys. In this study, we reassess lithostratigraphic data from the central part of the Tauern Window to reconstruct the post-Variscan evolution of this area, particularly the rift-related geometry of the European continental margin. The lithostratigraphy of the Alpine nappes reflects systematic variations of the structure of the European margin. The lowest tectonic units (Venediger nappe system, Eclogite Zone and Trögereck Nappe) are characterized by a thick succession of arkose-rich Bündnerschiefer-type sediments of probably Early Cretaceous age that we interpret as syn-rift sequence and which stratigraphically overlies thinned continental basement and thin pre-rift sediments. In contrast, the highest tectonic unit derived from Europe (Rote Wand Nappe) preserves a thick pre-rift sedimentary sequence overlying thinned continental basement, as well as a thick syn- to post-rift succession characterized by turbiditic Bündnerschiefer-type sediments of probable Cretaceous age. These observations point towards a highly segmented structure of the European rifted margin. We propose that this involved the formation of an outer margin high, partly preserved in the Rote Wand Nappe, that was separated from the main part of the European margin by a rift basin overlying strongly-thinned continental crust. The along-strike discontinuity of the Rote Wand Nappe is proposed to reflect the lateral variation in thickness of the outer margin high that resulted from margin-parallel segmentation of the European continental crust during highly oblique rifting antecedent to the opening of Alpine Tethys.
We investigate the evolution of the three‐dimensional thermal structure of a palaeo‐subduction channel exposed in the Penninic units of the central Tauern Window (Eastern Alps). Structural and ...petrological observations reveal a sheath fold with an amplitude of some 20 km that formed under high‐P conditions (~2 GPa). The fold is a composite structure that isoclinally folded the thrust of an ophiolitic nappe derived from Alpine Tethys Ocean onto a unit of the distal European continental margin, also affected by the high‐P conditions. This structural assemblage is preserved between two younger domes at either end of the Tauern Window. The domes deform isograds of the T‐dominated Barrovian metamorphism that itself overprints the high‐P metamorphism partly preserved in the sheath fold. Using Raman spectroscopy on carbonaceous material (RSCM), we are able to distinguish peak‐temperature domains related to the original subduction metamorphism from domains associated with the later temperature‐dominated (Barrovian) metamorphism. The distribution of RSCM temperatures in the Barrovian domain indicates a lateral and vertical decrease of peak temperature with increasing distance from the centres of the thermal domes. This represents a downward increase of palaeo‐temperature, in line with previous studies. However, we observe the opposite palaeo‐temperature trend in the lower limb of the sheath fold, namely an upward increase. We interpret this inverted palaeo‐temperature domain as the relic of a subduction‐related temperature field. Towards the central part of the sheath fold's upper limb, RSCM temperatures increase to a maximum of ~520°C. Further upsection in the hangingwall of the sheath fold, palaeo‐peak temperatures decrease to where they are indistinguishable from the peak temperatures of the overprinting Barrovian metamorphism. Peak‐temperature contours of the subduction‐related metamorphism are oriented roughly parallel to the folded nappe contacts and lithological layering. The contours close towards the northern, western and eastern parts of the fold, resulting in an eye‐shaped, concentric pattern in cross‐section. The temperature contour geometry therefore mimics the fold geometry itself, indicating that these contours were also folded in a sheath‐like manner. We propose that this sheath‐like pattern is the result of a two‐stage process that reflects a change of the mode of nappe formation in the subduction zone from thrusting to fold nappe formation. First, thrusting of a hot oceanic nappe onto a colder continental nappe created an inverted peak‐thermal gradient. Second, sheath folding of this composite nappe structure together with the previously established peak‐temperature pattern during exhumation. This pattern was preserved because temperatures decreased during retrograde exhumation metamorphism and remained less than the subduction‐related peak temperatures during the later Barrovian overprint. The fold ascended with diapir‐like kinematics in the subduction channel.
Previous work suggested a double collision suture, including ophiolites from two oceanic basins (Valais and Piemont‐Liguria), on the southern side of Monte Rosa (Penninic Alps, northern Italy). This ...area was studied using field mapping, microstructural analysis, and neutron texture goniometry. After its formation and eclogite‐facies metamorphism of continental and oceanic units, the suture was deformed by four successive folding and shearing events under greenschist‐facies conditions, all of them taking place between 40 and 28 Ma. After fold retrodeformation, the following tectonostratigraphy results, from base to top: Monte Rosa gneiss (European margin), Balma serpentinite/eclogite unit (Cretaceous crust of Valais ocean), Stolemberg gneiss (Iberia‐Briançonnais continent), Zermatt‐Saas and Tsaté ophiolites (Jurassic crust of Piemont‐Ligurian ocean), Sesia nappe (continental fragment off the Adria margin). The preservation of this lithological sequence suggests that deep‐seated deformation during multiple continent collision produces heterogeneous strain and extreme thinning of nappes but their original stacking order can still be reconstructed using kinematic analysis and overprinting criteria. This is due to the ductile nature of the collisional deformation which retains the continuity of tectonic contacts.
Seismic wave velocities and anisotropy can potentially discern lithologies and their structural configuration at depth. An increasing amount of data exists that indicates seismic anisotropy can be a ...valuable marker to identify internal deformation within deeply buried crust. Here, we present petrophysical properties of variably deformed felsic rocks that have been metamorphosed at blueschist and eclogite-facies conditions, representative of the bulk composition of the mid continental crust. The samples were collected from the Monte Mucrone area (Sesia Zone, Western Alps) and the Serra di Pigno, Farinole, and Tenda areas (Corsica). The mineral assemblages of all samples indicate that fluids were abundant during re-equilibration at HP conditions. Petrophysical properties were derived from ultrasonic measurements as well as calculated from crystallographic preferred orientations obtained by neutron texture goniometry. The results show that crystallographic preferred orientations are weak and yet the magnitude of seismic anisotropy produced by metamorphism of the felsic continental crust is highly variable, ranging from 1 to 12% for P waves and 1–14% for S waves depending on the strength of deformation fabrics. At the same time, absolute wave velocities remain low compared to more mafic rocks that have equilibrated at HP conditions. These results demonstrate that, other than their mafic equivalents, felsic HP rocks cannot be distinguished from their protoliths by wave velocities because their increase during HP metamorphism is too small. However, fluid availability during metamorphism and deformation causes strong variations in the seismic anisotropy of such lithologies, that might be distinguishable at depth.
•Felsic HP rocks are not seismically faster than crustal velocities.•Seismic anisotropy of felsic HP rocks is very variable.•Fluid availability increases the variability of seismic anisotropy.
The chemical composition of a rock has a first-order effect on the onset and duration of rock dehydration. We present a multiscale dataset of chemical heterogeneities found in a low-temperature ...serpentinite from the Mirdita ophiolite in Albania, and we explore the effects of such heterogeneities on slab dehydration during subduction. The dataset consists of chemical and geological mappings from the micron to the meter scale, spanning five orders of magnitude. At each scale, we investigate the interplay of metamorphic reactions as well as porosity and fluid production through thermodynamic modeling along a slab Moho P-T path typical for subducting plates. Notably, our results show that chemical heterogeneities are preserved, regardless of the observation scale, even in the case of local homogenization by events such as the lizardite-antigorite transition. Consequently, scale-invariant patterns of porosity evolution and fluid production along the P-T path emerge, with characteristic peaks for each dehydration reaction. As such, the dehydration behavior on the slab scale seems to be controlled by the processes on the millimeter scale, whereby resulting peaks correspond to pulsed slab fluid release localized in space and time at each scale, along the strike and along the dip of the subducting plate.
•Self-similar patterns of chemical heterogeneities found over at least four orders of magnitude.•Heterogeneities result in distinct peaks for fluid production on each scale.•Fluid pulses occur on the order of 0.5-0.9 Ma for reduced and as short as 0.1 Ma for oxidized serpentinite bulk compositions.
The tectonic structure of the Eastern Alps is heavily debated with successive geophysical studies that are unable to resolve areas of ambiguity (e.g., the presence of a switch in subduction polarity ...and differing crustal models). In order to better understand this area, we produce a high resolution Moho map of the Eastern Alps based on a dense seismic broadband array deployment. Moho depths were derived from joint analysis of receiver function images of direct conversions and multiple reflections for both the SV (radial) and SH (transverse) components, which enables us to map overlapping and inclined discontinuities. We observe the European Moho to be underlying the Adriatic Moho from the west up to the eastern edge of the Tauern Window. East of the Tauern Window, a sharp transition from underthrusting European to a flat and thinned crust associated with Pannonian extension tectonics occurs, which is underthrust by both European crust in the north and by Adriatic crust in the south. The Adriatic lithosphere underthrusts northward below the Southern Alps and becomes steeper and deeper towards the Dinarides where it dips towards the north-east. Our results suggest that the steep high velocity region in the mantle below the Eastern Alps, observed in tomographic studies, is likely to be of European origin.
•A high resolution Moho map of the Eastern Alps.•Mapping of overlapping Moho discontinuities (where underthrusting occurs).•Evidence for a continuous European plate derived southward subducting interface.•Thinned Pannonian basin connected crust is underthrust by European and Adriatic crust.
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