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The Aegean region (Greece, western Turkey) is one of the best studied continental extensional provinces. Here, we provide the first detailed kinematic restoration of the Aegean region since 35 Ma. The region consists of stacked upper crustal slices (nappes) that reflect a complex paleogeography. These were decoupled from the subducting African-Adriatic lithospheric slab. Especially since ∼25 Ma, extensional detachments cut the nappe stack and exhumed its metamorphosed portions in metamorphic core complexes. We reconstruct up to 400 km of trench-perpendicular (NE-SW) extension in two stages. From 25 to 15 Ma, the Aegean forearc rotated clockwise relative to the Moesian platform around Euler poles in northern Greece, accommodated by extensional detachments in the north and an inferred transfer fault SE of the Menderes massif. The majority of extension occurred after 15 Ma (up to 290 km) by opposite rotations of the western and eastern parts of the region. Simultaneously, the Aegean region underwent up to 650 km of post-25 Ma trench-parallel extension leading to dramatic crustal thinning on Crete. We restore a detachment configuration with the Mid-Cycladic Lineament representing a detachment that accommodated trench-parallel extension in the central Aegean region. Finally, we demonstrate that the Sakarya zone and Cretaceous ophiolites of Turkey cannot be traced far into the Aegean region and are likely bounded by a pre-35 Ma N-S fault zone. This fault became reactivated since 25 Ma as an extensional detachment located west of Lesbos Island. The paleogeographic units south of the İzmir-Ankara-Sava suture, however, can be correlated from Greece to Turkey. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the original version of this article, one reference was incorrect. The following change was necessary: [ABSTRACT FROM AUTHOR]

Accuracy of hypocenter location, in particular focal depth, is a precondition for high‐resolution seismotectonic analysis of natural and induced seismicity. For instance, linking seismicity with mapped fault segments requires hypocenter accuracy at the sub‐kilometer scale. In this study, we demonstrate that inaccurate velocity models and improper phase selection can bias absolute hypocenter locations and location uncertainties, resulting in errors larger than the targeted accuracy. To avoid such bias in densely instrumented seismic networks, we propose a coupled hypocenter‐velocity inversion procedure restricted to direct, first‐arriving, mainly upper‐crustal Pg and Sg phases. On the basis of synthetic tests and selected ground‐truth events we demonstrate that a sub‐kilometer hypocenter accuracy can be achieved by regional‐scale, three‐dimensional Pg and Sg velocity models combined with dynamic phase selection and a non‐linear location algorithm. The tomographic inversion uses about 60,000 Pg and 30,000 Sg quality‐checked phases of local earthquakes in the Central Alps region. The derived models image the VP and VS structure of the Central Alps upper crust at unprecedented resolution, including small‐scale anomalies such as those caused by Subalpine Molasse units below the Alpine front. The relocation procedure is applied to more than 18,000 earthquakes and the relocated hypocenters reveal previously unrecognized seismogenic structures, for instance in the Swiss Molasse basin south of Bern. The ML 4.6 Urnerboden earthquake of 2017 is used as an example to demonstrate how the derived 3D velocity structure and relocated hypocenters can be jointly interpreted to constrain the lithology hosting upper‐crustal seismicity in the Central Alps. Plain Language Summary: To better understand how mountain belts like the European Alps presently deform and what are the plate‐tectonic forces driving this deformation requires accurate knowledge of the location of earthquakes within these continental collision zones. In this study, we achieve an accuracy of less than a kilometer for earthquake locations in Switzerland, based on detailed knowledge of the subsurface structure of the Earth's crust. We use three‐dimensional tomographic imaging methods to improve subsurface structural models of the Central Alps. These models also provide new insights into the geological structure of this mountain range and in combination with the improved earthquake locations allow for detailed studies of present‐day tectonic processes. Key Points: Sub‐kilometer hypocenter accuracy is achieved with dynamically selected Pg and Sg phases, in combination with 3D crustal velocity modelsNew 3D VP and VS models image the upper crust of the Central Alps region at unprecedented resolutionJoint interpretation of relocated hypocenters and seismic velocities can constrain lithologies hosting seismicity in the Central Alps [ABSTRACT FROM AUTHOR]

The Cenozoic foreland fold and thrust belt of the external Dinarides along the eastern shore of the Adriatic Sea shows an overall NW-SE structural strike that changes to E-W in its central part, between Zadar and Mostar. This change is associated with a dextrally transpressive zone, named Split-Karlovac Fault. Segments of this fault straddle the Eo-Oligocene flexural foreland basin system of the external Dinarides. Two balanced cross-sections across the northern and southern segments of this transverse fault zone document highly contrasting styles of deformation and amount of shortening. The northern segment across Velebit Mountain is characterized by a triangle structure with a minimum shortening of 44 km. This triangle structure is formed by a set of thick-skinned top-SW thrust duplexes, topped by a thin-skinned passive top-NE roof backthrust. By contrast, the southern segment, traversing north of Split, shows a thin-skinned top-SW to top-S directed nappe stack, associated with a minimum shortening of 127 km and rooting into a basal detachment in the Paleozoic basement. To better understand parameters controlling these contrasting styles of deformation, we modelled the flexural response of the foreland lithosphere that provided the accommodation space for the Eocene to Oligocene syn-orogenic Promina Beds, a prevailingly carbonate-clastic and conglomerate-bearing sequence making a part of the foreland basin fill. Tectonic load exerted by the hinterland nappe stack was estimated using the two balanced cross-sections. Estimates of tectonic load allowed modelling the amount of flexural response that yielded depth and shape of the basin containing the Promina Beds. The best fitting modelling results provided additional confidence in the validity of the balanced cross-sections. It is shown that shortening in the two structurally contrasting segments of the thick-skinned thrust belt were contemporaneous with dextral strike-slip along the thick-skinned Split-Karlovac Fault and coeval with sedimentation of the Promina Beds. We propose that the Velebit triangle structure acted as a back-stop that prevented the propagation of the deformation front towards the SW. Instead shortening was transferred along the Split-Karlovac Fault into the southern transect, where deformation propagated towards the foreland along a successively shallowing stepped detachment. The contrasting style of Eo-Oligocene deformation probably resulted from the interplay of Permo-Triassic evaporites with the reactivation of inherited Middle Triassic normal faults to both sides of the transpressive zone. • Nappe stack vs. triangle structure in the external Dinarides fold and thrust belt. • Substantial along-strike difference of crustal shortening. • Effects of mechanically weak lithologies on the style of deformation. • Lithosphere deflection modelling in combination with balanced cross-sections. • Impacts of a transverse zone on the flexural foreland basin system geometry. [ABSTRACT FROM AUTHOR]

An ophiolitic mélange of Avala Mountain located south of Belgrade was studied to obtain age data from blocks of radiolarian cherts and to enable better understanding of age and nature of this mélange. The studied area is located south of Avala Mt. and its geotectonic position is rather obscure. The obtained data allow us to determine radiolarians from five samples; one is of Late Anisian to Early Ladinian, and four of them are of Middle Jurassic (Late Bathonian-Early Callovian) age. The finding of Triassic as well as Jurassic age radiolarians in one and the same mélange suggests that this mélange formed during obduction of the Western Vardar ophiolites. [ABSTRACT FROM AUTHOR]