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In-situ 40 Ar/ 39 Ar laser ablation dating of white-mica grains was performed on samples from the footwall of a crustal-scale extensional fault (Katschberg Normal Fault; KNF) that accommodated eastward orogen-parallel displacement of Alpine orogenic crust in the eastern part of the Tauern Window. This dating yields predominantly cooling ages ranging from 31 to 13 Myr, with most ages clustering between 21 and 17 Myr. Folded white micas that predate the main Katschberg foliation yield, within error, the same ages as white-mica grains that overgrow this foliation. However, the absolute ages of both generations are older at the base (20 Myr) where their grain size is larger (300–500 μm), than at the top and adjacent to the hangingwall (17 Myr) of this shear zone where grain size is smaller (< 100–300 μm). This fining-upward trend of white-mica grain size within the KNF is associated with a reduction of the closure temperature from the base (~ 445 °C) to the top (< 400 °C) and explains the counter-intuitive trend of downward-increasing age of cooling in the footwall. The new data show that rapid cooling within the KNF of the eastern Tauern Window started sometime before 21 Myr according to the 40 Ar/ 39 Ar white-mica cooling ages and between 25–21 Myr according to the new Rb/Sr white-mica ages, i.e., shortly after the attainment of the thermal peak in the Tauern Window at ~ 25 Myr ago. These new data, combined with literature data, support earlier cooling in the eastern part of then Tauern Window than in the western part by some 3–5 Myr. [ABSTRACT FROM AUTHOR]

Abstract: Thermochronological, structural and kinematic analyses demonstrate the influence of Late Paleozoic basement structures on the localization and evolution of the Rhine–Bresse Transfer Zone (RBTZ), a central segment of the European Cenozoic Rift System. Zircon and apatite fission track data indicate that the Paleozoic crystalline basement and its Permo-Triassic cover, exposed in the La Serre Horst, experienced a Middle Jurassic to Early Cretaceous heating event which was followed by two distinct periods of cooling. A first cooling event occurred in the Early Cretaceous and is probably related to thermal relaxation. A second one, started at around 38 Ma, is interpreted to reflect exhumation that was induced by fault reactivation along the Late Paleozoic Burgundy Trough System during Eocene–Oligocene rifting and the formation of the RBTZ. This fault reactivation resulted in a complex fault pattern and local stress field perturbations in the surroundings of the pre-existing horst structure. Substantial extension was achieved by ENE–WSW striking normal faults that trend highly oblique to the dominant strike of the Rhine and Bresse Graben rifts. Seismic reflection data show that these major normal faults are typically associated with extensional flexures and oriented parallel to pre-existing Late Paleozoic basement faults of the Burgundy Trough. Paleostress analyses yield overall NW–SE extension during the Eo-Oligocene, slightly oblique to the structural trend of the RBTZ, and additionally, local stress field perturbations induced by the reactivation of pre-existing faults. Reactivation of Paleozoic structures in the RBTZ is of extensional rather than of strike-slip character indicating that the RBTZ is forming a separate oblique graben segment within the European Cenozoic Rift System rather than a sinistral strike slip transform zone supposedly connecting Rhine and Bresse graben structures. [Copyright &y& Elsevier]

Abstract: Analogue experiments on oblique rifting and subsequent transpressional reactivation were performed with two-layer slabs of sand and silicone. In this brittle–viscous system, transtensional and transpressional wrench faulting was induced by movements of a basal rigid plate. The dynamically scaled analogue models are confronted with the structural evolution of the Rhine–Bresse transfer zone (RBTZ) that linked Palaeogene rifting in the Upper Rhine and Bresse Grabens and that appears to have been transpressively reactivated in Neogene to recent times. Fault patterns produced in the sand layer above the basal silicone layer are compared with structural elements in the sedimentary cover, separated from the basement by an evaporitic décollement layer. In order to investigate strain-rate dependence of fault reactivation and graben inversion, transpressional shortening was performed under different displacement rates. Experimental results suggest that the reactivation of pre-existing structures in a brittle cover above a viscous décollement is strongly dependent on the strain rate within the viscous layer. Under low to intermediate displacement rates (2.6cmh-1), deformation concentrates within the basal viscous layer and former normal faults within the cover are not reactivated. The reactivation at higher displacement rates (5cmh-1) results in a complete inversion of graben structures within the cover. Ongoing shortening produces lobed thrust fronts, which crosscut pre-existing normal faults. Late Pliocene to recent en-échelon aligned folds and isolated thrust faults in the cover of the RBTZ are attributed to thick-skinned reactivation of basement faults. A comparison of natural and experimentally obtained structures suggests that fault reactivation occurred under low displacement rates (<1mm/a). This results in a low mechanical coupling between basement and cover in areas with significantly thick décollement layers, providing an explanation for decoupled stresses between basement and cover, such as observed in the northern Jura Mountains. [Copyright &y& Elsevier]

Central Anatolia exposes previously buried and metamorphosed, continent-derived rocks – the Kırşehir 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 Kırşehir 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. [ABSTRACT FROM AUTHOR]

Abstract: 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 produced intense deformation of an Eocene-age nummulitic limestone under lower anchizone metamorphic conditions (slightly below 300 °C). Two types of microfabrics developed primarily by dislocation creep accompanied by dynamic recrystallisation in the absence of twinning. Coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry. Their texture (crystallographic preferred orientation, CPO) is characterised by two c-axis maxima, symmetrically oriented at 15° from the normal to the macroscopic foliation. Non-coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterised 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, which developed in coaxial kinematics, favour activity of <10–11> and <02–21> slip along the f and r planes, respectively, with minor contributions of basal- slip. In contrast, the monoclinic textures, which developed during simple shear, are most suited for duplex slip along the basal plane. The transition between the dominating slip systems for the orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallisation upon texture development. Since oblique c-axis maxima documented in the literature are most often rotated not with but against the shear sense, 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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]