D. Pedreira

Alpine exhumation of the central Cantabrian Mountains, Northwest Spain

The Cantabrian Mountains extend along the Atlantic coast of northern Spain and are known to have experienced an Alpine phase of deformation, reactivating well-expressed Variscan structures. They form the westward continuation of the Pyrenean range and were similarly uplifted consequently to the convergence between the Iberian and European plates. Nevertheless, due to the scarcity of syntectonic sediments and structural markers in a large outcrop of Variscan basement, little is known about the precise timing and amount of the Alpine exhumation phase in the Cantabrian Mountains. We present a new low-temperature thermochronology data set, composed of nine apatite fission track (AFT) and six zircon (U-Th)/He (ZHe) ages, sampled along structurally well-constrained N-S profiles through the central part of the Cantabrian Mountains and complemented by 3-D thermokinematic modeling. The occurrence of Eocene-Oligocene AFT and ZHe ages in the center of the profiles allows us to frame the period of Alpine exhumation from 39 to 29Ma, at a rate of 0.24–0.3 kmMyr . Moreover, the reset ZHe ages imply significant burial of the samples, by up to 8–10 km in the center of the range. Therefore, the Alpine exhumation phase was significant, and synchronous to the main phase of exhumation in the central Pyrenees, although exhumation rates were an order of magnitude lower. Three-dimensional thermokinematic modeling of the data confirms the timing of uplift of this area, but its resolution is limited by the relatively small number of reset ages over a large area.

Mantle exhumation and metamorphism in the Basque-Cantabrian Basin (N Spain): Stable and clumped isotope analysis in carbonates and comparison with ophicalcites in the North-Pyrenean Zone (Urdach and Lherz)

The presence of ophicalcites in serpentinized peridotites together with fragments of these rocks in Cretaceous breccias along several North-Pyrenean basins led to the interpretation of complete mantle exhumation to the seafloor. The westernmost outcrop of peridotites in the Pyrenean-Cantabrian belt is located in Ziga (eastern Basque-Cantabrian Basin), associated to a band of HT metamorphism related to the Leiza fault (Marble Unit). We present a petrological and geochemical study of the marbles and Ziga peridotite-hosted calcite, including standard stable isotope composition and clumped isotope geothermometry. These isotopic techniques allow the determination of different types of formational fluids and crystallization temperatures, and are a useful tool for studying carbonation processes in hyperextended basins. Fieldwork and analytical studies lead us to conclude that during the opening of the Bay of Biscay, mantle rocks were unroofed at the base of the sedimentary pile of the eastern Basque-Cantabrian Basin. However, the ophicalcite veins were recrystallized from meteoric fluids at low temperatures (≤49°C). The primary carbonate phase may have been formed either during the mid-Cretaceous unroofing of the mantle or in a post-exhumation stage. The process of mantle exhumation was accompanied with HT-LP metamorphism and fluid circulation along major faults that reset the marine isotopic signature in the nearest marbles. For comparison, ophicalcites from Urdach and Lherz (North-Pyrenean Zone) were included in the clumped isotope study. Results show that they were recrystallized from hot (∼200–230°C), saline fluids, and from meteoric fluids at near ambient temperatures (∼32–42°C), respectively.

The Pre-Andean Phases of Construction of the Southern Andes Basement in Neoproterozoic–Paleozoic Times

During the late Neoproterozoic and Paleozoic times, the southern Andes of Argentina and Chile (21o–55o S) formed part of the southwestern margin of Gondwana. During this period of time, a set of continental fragments of variable extent and allochtony was successively accreted to that margin, resulting in six Paleozoic orogenies of different temporal and spatial extension: Pampean (Ediacaran–early Cambrian), Famatinian (Middle Ordovician–Silurian), Ocloyic (Middle Ordovician–Devonian), Chanic (Middle Devonian–early Carboniferous), Gondwanan (Middle Devonian–middle Permian), and Tabarin (late Permian–Triassic). All these orogenies culminate with collisional events, with the exception of the Tabarin and a part of the Gondwanan orogenies that are subduction-related.

Lithospheric structure of the Western Pyrenees- Cantabrian Mountains based on 3D modelling of gravity anomalies and geoid undulations: preliminary results

Los braquiopodos retzidinos son una fraccion menor de las faunas devonicas de la CordilleraCantabrica (Norte de Espana). Aparte de un par de formas raras, impublicadas, del Praguiense delDominio Palentino y del Emsiense inferior del Astur-Leones, proximas al genero Rhynchospirina, ellinaje alcanzo su maximo de diversidad en la parte superior del Emsiense, con dos especies del generoRetzia, R. adrieni y R. cf. prominula, Cooperispira subferita y, quizas, una forma impublicada dePlectospira. El grupo no es conocido en el resto del Devonico y reaparece en el Pensilvaniense con algunasformas del genero Hustedia. En este trabajo se propone un nuevo taxon de la Familia Retziidae,Argovejia n.gen., de la parte final del Emsiense superior de Asturias y Leon, constituido por su especietipo,A. talenti n.sp. y, quizas, por las formas del Emsiense superior del Macizo Armoricano (Francia)Retzia haidingeri var. armoricana y Retzia haidingeri var. dichotoma.The Ronda Depression is filled by Neogene sediments on the boundary between Subbeticreliefs, with NE-SW structural trends, and the frontal Subbetic Chaotic Complexes. The folding stylein the Subbetic Units of Western Betics is strongly controlled by the rheology of the rocks: thick andmassive beds of Jurassic limestones over Triassic marls and gypsum with plastic behaviour. Main deformationstructures in the sedimentary infill of the Ronda depression are simultaneous box folds withNNE-SSW and WNW-ESE trends that only affect its southwestern part. This distribution of folds isa consequence of the inherited fold trend that affected the basement during Early Burdigalian age.

International Meeting of Young Researchers in Structural Geology and Tectonics (YORSGET-08): introduction

The Subandean Basins of South America extending from Trinidad to Tierra del Fuego have been the object of intensive exploratory activities (Fig. 1). The largest amount of hydrocarbons discovered during the last 30 years in these basins was found in complex structural terrains. A total of 59 Billion Barrels of Oil Equivalent (BBOE) have been discovered in areas affected by compressional tectonics. Of these basins, the largest discoveries are in the Furrial Trend of Venezuela (24 BBOE), followed by the Chaco area in Bolivia and Argentina (13 BBOE), the Llanos Foothills of Colombia (4.4 BBOE), and the Madre de Dios Basin of Peru (4.2 BBOE).