Strike slip tectonics and transtensional deformation in the Aegean region and the Hellenic arc: Preliminary results

Recently acquired offshore seismic and swath bathymetry data from the Hellenic Arc, the Ionian Sea and the South and North Aegean Sea, including the Hellenic Volcanic Arc and the Cyclades plateau, along with geological and tectonic data from Plio-Quaternary basins exposed on the Hellenic Arc indicate that strike slip tectonics has played a major role in the southwestward extension of the Aegean crustal block, the development of the offshore neotectonic basins and the spatial distribution of the volcanic activity along the Volcanic Arc. Transtensional deformation, accommodated by (sinistral or dextral) strike slip zones and related extensional structures, prevail throughout Plio-Quaternary, since the North Anatolian Fault broke westwards into the North Aegean. Incipient collision of the Hellenic Forearc south of Crete with the Libyan promontory and consequent lateral escape tectonics led to the segmentation of the Hellenic Arc in distinct blocks, which move southwestwards independently from each other and are bounded by strike slip faults.

Vertical strain partitioning in hot Variscan crust: Syn-convergence escape of the Pyrenees in the Iberian-Armorican syntax

A new structural map of the Paleozoic crust of the Pyrenees based on an extensive compilation and new kinematic data allows for the evaluation of the mechanical coupling between the upper and lower crust of the abnormally hot foreland of the Variscan orogen of SW Europe. We document partitioning between coeval lower crustal lateral flow and upper crustal thickening between 310 and 290 Ma under an overall dextral transpressive regime. Partitioning also involved syn-convergence transtensional gneiss domes emplacement during this period. Late orogen-normal shortening of the domes and strain localization in steep crustal-scale transpressive shear zones reflects increasing coupling between the lower crust and the upper crust. The combination of dextral transpression and eastward flow in the Pyrenees results from the shortening and lateral escape of a hot buoyant crust along the inner northern limb of the closing Cantabrian orocline at the core of the Iberian-Armorican arc between ca. 305 and 295 Ma. Delamination or thermal erosion of the lithosphere enhanced orocline closure and explains (1) the switch from crust- to mantle-derived magmatism in the Iberian-Armorican arc and (2) the abnormally hot and soft character of the Pyrenean crust that escaped the closing syntax.

The Timing of Strike-Slip Deformation Along the Storstrømmen Shear Zone, Greenland Caledonides: U–Pb Zircon and Titanite Geochronology

The Storstrømmen shear zone (SSZ) in the Greenland Caledonides is widely interpreted to have formed in a transpressional regime during sinistral, oblique collision between Baltica and Laurentia in the Silurian to Devonian. New mapping of the SSZ at Sanddal documents a 100 m thick, greenschistfacies mylonite zone cutting the eclogite to amphibolite-facies gneiss complex. We present U–Pb ion probe geochronology on zircon and titanite from a variety of lithologies that shows the SSZ was active from late Devonian to the Carboniferous (at least until 350 Ma). The age of thrusting in the foreland is not well known, but must be younger than the age of eclogite-facies metamorphism at ~400 Ma. It is, therefore, possible that contraction is the same age as strike-slip motion, and that transpression is a viable model. The timing of the SSZ is synchronous with dextral strike-slip displacement on the Germania Land deformation zone. Simultaneous displacement on sinistral and dextral, conjugate shear zones suggests that the SSZ is part of a strikeslip fault system that led to lateral escape of material northward (present day coordinates) during the waning stages of plate convergence between Laurentia and Baltica.SOMMAIRELa zone de cisaillement de Storstrømmen (SSZ) dans les Calédonides du Groenland est généralement comprise comme ayant été formée durant un régime de transpression sénestre lors de la collision oblique entre Baltica et Laurentie, du Silurien au Dévonien. Une nouvelle cartographie de la SSZ à Sanddal décrit une zone de 100 m d’épaisseur de mylonite au faciès des schistes verts qui recoupe un complexe de gneiss au faciès éclogite à amphibolite. Notre analyse géochronologique par sonde ionique U-Pb sur zircon et titanite sur diverses lithologies, montre que la SSZ a été active de la fin du Dévonien jusqu’au Carbonifère (au moins jusqu’à 350 Ma). L’âge du chevauchement dans l’avant-pays n’est pas bien connue, mais il doit être plus jeune que le métamorphisme au faciès d’éclogite à ~400 Ma. Il est donc possible que la contraction soit du même âge que le mouvement de coulissage, et que la transpression soit un modèle viable. La chronologie de la SSZ est synchrone au mouvement de coulissage dextre de la zone de déformation de Germania Land. Les déplacements simultanés, sénestre et dextre, sur des zones de cisaillement conjuguées permettent de penser que la SSZ fait partie d’un système de décrochement qui a engendré une éjection latérale de matériau vers le nord (selon les coordonnées actuelles) durant les stades de convergence des plaques Laurentie et Baltica.