Oscar Fernández

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Inversion of the Austroalpine Triassic salt-bearing passive margin, represented by the Northern Calcareous Alps (Eastern Alps), started in the Late Jurassic. Subsequent deformation during the Cretaceous and Cenozoic mostly preserved the Late Jurassic deformation fabric in the central Northern Calcareous Alps, making it an outstanding location to understand the early history of inversion of salt-bearing margins. Thrusting and folding in the central NCA during the Late Jurassic were strongly conditioned by the distribution of Triassic salt structures, the thickness of supra-salt stratigraphy, the lateral propagation of deformation, and the possible influence of sub-salt basement faults. Syn-orogenic sediments make it possible to reliably reconstruct the timing of structural inversion. The description of Late Jurassic structures presented here indicates that initial inversion of the Northern Calcareous Alps led to the development of coherent deformation systems that accumulated limited amounts of shortening, totaling few tens of kilometers. This differs from previous interpretations of Late Jurassic deformation of the area, that involve major amounts of allochthony (many tens of kilometers). As a specific example of coherent structural development, we present here an 80 km long linked system of thrusts and folds (the Totengebirge–Trattberg contractional system), whose outstanding continuity has gone previously unrecognized. The anatomy of this system and its temporal evolution are described in detail and discussed in the framework of the Jurassic to recent evolution of the Eastern Alps.

Michel Bestmann

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Coarse-grained quartz veins from the Prijakt Nappe (Austroalpine Unit, Schober Mountains, Eastern Alps), that formed under amphibolite facies conditions, were overprinted by lower greenschist facies deformation. During overprinting, subgrain rotation (SGR) recrystallization was the dominant mechanism assisting the evolution from protomylonite to (ultra)mylonite. The initial Ti-concentration [Ti] (3.0-4.7 ppm) and corresponding cathodoluminescence (CL) signature of the quartz vein crystals were reset to different degrees mainly depending on the availability of fluids and their partitioning across the microstructure. The amount of strain played a subordinate role in resetting. In recrystallized aggregates the most complete re-equilibration ([Ti] of 0.2-0.6 pm) occurred in strain shadows surrounding quartz porphyroclasts, acting as fluid sinks, and in localized shear bands that channelized fluid percolation. We applied a correlative multi-analytical workflow using optical and electron microscopy methods (e.g. electron backscatter diffraction and cathodoluminescence) in combination with secondary ion mass spectroscopy for [Ti] measurement. The most efficient [Ti] resetting mainly occurs along wetted high angle boundaries (misorientation angle >10-15°), and to a minor extend (partial resetting) along dry low angle boundaries (<10-15°). This key-study prove for the first time that pure subgrain rotation recrystallization in combination with dissolution-precipitation under retrograde condition is able to provide microstructural sites to apply the TitaniQ geothermobarometer at deformation temperatures down to 300-350 °C provided that information on pressure and Ti-activity is available.