Multigrain concentrates of hornblende and muscovite together with whole-rock slate/phyllite samples have been dated Variscan deformation systematically prograded diachronously eastward across the orogen as new crustal material was added along the front of the developing orogenic wedge. However, the entire orogen remained tectonically active with different structural features forming at different times and at different places. An average propagation rate of ca. 5 kmlm.y. is suggested by consideration of a 20-25 Ma difference in correlative fabric ages and present separations.

A sedimentological and geochemical study of the Lago Enol sequence (Cantabrian Mountains, Northern Spain) together with detailed geomorphological mapping provides a first record of glacier evolution and climate change over the last 40,000 years in the

ABSTRACT. The Andean Paleozoic basement of the Cordón del Plata (Argentina) consists of two sets of rocks showing different stratigraphy, structure and metamorphism. The lower one is represented by the pre-Carboniferous (Devonian?) Vallecitos beds. These rocks have been affected by folds and associated cleavage, developed under low-grade metamorphic conditions and related to the Chanic orogenic event of the Famatinian Orogenic Cycle (Upper Devonian-Lower Carboniferous). The Vallecitos beds is pre-orogenic to the Chanic deformation event and must have been deposited in a fore-arc basin located on the active margin of Chilenia, before its collision with the passive margin of Gondwana. The upper set unconformably rests on the Vallecitos beds and consists of the Late Carboniferous El Plata Formation, and the Río Blanco Conglomerates, probably Late Carboniferous-Permian in age. These rocks have been affected by eastdirected thrusts and associated folds formed under very low-grade to non-metamorphic conditions. This deformation can be related to the San Rafael phase (Gondwanan Orogen). The El Plata Formation was deposited in an extensional back-arc basin while the Río Blanco conglomerates must have been deposited in a retro-arc basin, both of them on the active margin of Gondwana. The Choiyoi Group, essentially volcanic and Permo-Triasic in age, rests unconformably on the previously described successions and was deposited in an extensional setting (pre-orogenic stage) associated with the beginning of the Andean Cycle. This cycle lead to the uplift of the Frontal Cordillera during the Cenozoic and the deposition of thick continental units at the base of the Cordón del Plata in Neogene-Quaternary times.

No abstract

The fi nal stages of the Variscan orogeny (mostly Carboniferous) in the Western European Variscan belt involved the development of the Iberian-Armorican arc, which is cored by the Cantabrian zone (NW Iberia). TheCantabrian zone is the foreland of the Western European Variscan belt, and it is interpreted to record the waning stages of the closure of the Rheic Ocean. The distalmost tectonic units within the Cantabrian zone (the Cuera Unit and the Picos de Europa Province) were the last tectonic units emplaced at the core of the Western European Variscan belt orocline. Together, they form an imbricate system and associated wedge-top basins that are key to understanding the development of the orocline. The emplacement of the Cuera Unit and the Picos de Europa Province occurred in the latest Pennsylvanian, between Moscovian and Gzhelian times. New detailed mapping together with stratigraphic, sedimentologic, and biostratigraphic data analysis of syntectonic successions and structural information constrain the timing and evolution of this imbricate system. Our analysis indicates that the thrust sheets were emplaced roughly perpendicular to previous tectonic units of the Cantabrian Variscan foreland fold-and-thrust belt, most probably during the oroclinal bending of the SW European Variscan belt that formed the Iberian-Armorican arc. The N-S-directed imbricate system was characterized by a shallow dip of the topographic surface (α < 1°), allowing for the development of wedge-top basins. The large amount of shortening (>150 ± 15 km) and complex structure of the orogenic wedge are thought to result from the progressive increase in the dip of the basal décollement during bending of the underlying Gondwana lithosphere and may refl ect the closure of the Iberian-Armorican arc.