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[1] 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-P1Ms-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 [sup.40][Ar/.sup.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 rollback in the Carpathians. Citation: Ustaszewski, K., A. Kounov, S. M. Schmid, U. Schaltegger, E. Krenn, W. Frank, and B. Fugenschuh (2010), Evolution of the Adria-Europe plate boundary in the northern Dinarides: From continent-continent collision to back-arc extension, Tectonics, 29, TC6017, doi: 10.1029/2010TC002668.

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 [sup.40]Ar/[sup.39]Ar 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. Citation: Wiederkehr, M., M. Sudo, R. Bousquet, A. Berger, and S. M. Schmid (2009), Alpine orogenic evolution from subduction to collisional thermal overprint: The 40Ar/39Ar age constraints from the Valaisan Ocean, central Alps, Tectonics, 28, TC6009, doi: 10.1029/2009TC002496.

This study investigates spatial and temporal interactions of thin- and thick-skinned tectonics in a classical foreland setting located at the front of the Jura fold-and-thrust belt in eastern France. The working area coincides with the intracontinental Rhine-Bresse Transfer Zone and represents the most external front of the deformed Alpine foreland. The investigation combines analyses of largely unpublished and newly available subsurface information with our own structural data, including an exhaustive paleostress analysis and geomorphologic observations. Results are provided in the form of a new tectonic map and a series of regional cross sections through the study area. The Besancon Zone, forming the most external part of the thin-skinned fold-and-thrust belt, encroached onto the Eo-Oligocene Rhine-Bresse Transfer Fault System until early Pliocene times. Thrust propagation was largely controlled by the Late Paleozoic to Paleogene preexisting fault pattern that characterizes the Rhine-Bresse Transfer Zone. Thick-skinned deformation, dominant throughout the Avant-Monts Zone located farther to the west, was associated with compressional to transpressional reactivation of such faults. Overprinting and crosscutting criteria of fault slip data allow distinguishing between systematically fanning maximum horizontal stress axes that define the front of the thin-skinned Jura fold-and-thrust belt and consistently NW--SE directed maximum horizontal stress axes that characterize deformation of the autochthonous cover of the foreland, which is affected by thick-skinned tectonics. Tectonic and geomorphic analyses indicate that thick-skinned tectonics started at a very late stage of foreland deformation (post-early Pliocene). Geomorphic observations imply that deformation between Mesozoic cover and basement is locally still decoupled. However, overprinting relationships and recent seismicity suggest that present-day tectonic activity is thick skinned, which probably reflects ongoing tectonic underplating in the Alpine foreland.

[1] This study investigates the formation of the northernmost anticlines of the late Miocene to early Pliocene thin-skinned Jura fold-and-thrust belt and provides evidence that a transition to thick-skinned tectonics did occur in this particular area during the late Pliocene. The northernmost anticlines of the Jura fold-and-thrust belt are characterized by pronounced along-strike asymmetries that were predetermined by a fault pattern inherited from Paleogene Upper Rhine Graben rifting. This fault pattern had disrupted the Triassic basal decollement of the Jura Mountains and controlled the nucleation of thrusts and folds, as well as transfer zones during the generally (N)NW directed transport of the detached sedimentary cover. Sinistral, transpressive oblique ramps nucleated along Paleogene, NNE trending basement normal faults and led to a northward protrusion of the Jura front, encroaching onto the southernmost Upper Rhine Graben. Shortening across the frontal anticlines is greatest along the oblique ramps and decreases along strike toward the east, necessitating a gentle clockwise rotation of the detached sediments. Despite the fact that the stress field in the sedimentary cover remained unchanged, thin-skinned folding and thrusting came to a halt in the early Pliocene, giving way to thick-skinned tectonics, very probably governing neotectonic activity in the area. This transition might represent a geodynamic reorganization of the northwestern Alpine foreland. Citation: Ustaszewski, K., and S. M. Schmid (2006), Control of preexisting faults on geometry and kinematics in the northernmost part of the Jura fold-and-thrust belt, Tectonics, 25, TC5003, doi: 10.1029/2005TC001915.

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]