Caracterización estructural y magnética de la discordancia sarda en el sector central de la Zona Axial pirenaica (La Seu d'Urgell, Lleida)

Estudio realizado desde el punto de vista de la geología estructural, en un sector de la Zona Axial pirenaica concretamente en el domo de l'Orri, donde la discordancia "sarda" tiene carácter cartográfico. La discordancia "sarda", supone una interrupción en la sedimentación relacionada con un evento orogénico y separa el Ordovícico superior de una serie más antigua constituida por materiales del Cambro-Ordovícico. En la zona de estudio, estos materiales están representados por la Fm. Rabassa y Fm. Jújols. En estos materiales, se han identificado tres etapas de deformación (D1, D2 y D3). La etapa D2 es la que está más bien desarrollada y define la macroestructura de la zona. Los materiales suprayacentes (Ordovícico superior) e infrayacentes (Cámbro-Ordovícicos) a la discordancia “sarda” en la zona de estudio, han sufrido las mismas etapas de deformación y presentan geometrías complejas que resultan de la interferencia de pliegues de las sucesivas etapas dando a escala macroestructural un interferencia de pliegues de tipo 2.<br /

Aplicación de la Anisotropía de la Susceptibilidad Magnética (ASM) al estudio de flujos de lava y materiales volcanoclásticos. Ejemplo de la Sierra del Cadí.

La cuenca stephano-pérmica del Cadí se localiza en el extremo sur de la Zona Axial (Pirineos Orientales) y es el resultado del complejo régimen tectónico imperante durante el Pérmico inferior junto con la actividad magmática asociada. La aplicación de la anisotropía de la susceptibilidad magnética (ASM) al estudio de flujos de lava y materiales volcanoclásticos (782 muestras tomadas en 64 estaciones) junto con un reconocimiento petrográfico y un estudio paleomagnético ha permitido ahondar en esta técnica para este tipo de materiales. A escala mesoestructural y microestructural se ha observado que la lineación magnética de las fábricas es paralela a la dirección de flujo o queda contenida en su plano y se reconoce una dirección principal del flujo en E-W y dos secundarias en dirección N-S y NW-SE. Además, se han establecido 9 tipos de fábricas magnéticas y dos de ellas son características de dos de los tipos litológicos reconocidos. El estudio paleomagnético ha permitido reconocer la existencia de una componente primaria pérmica y dos componentes secundarias. Los minerales que contribuyen a la susceptibilidad magnética son principalmente paramagnéticos y la magnetita y los que contribuyen a la magnetización son principalmente hematites y también magnetita.<br /

Axial longitudinal flow in volcaniclastic materials of the Late-Carboniferous-Permian Cadí basin (Southern Pyrenees) determined from Anisotropy of Magnetic Susceptibility

The aim of this work is the application of the anisotropy of magnetic susceptibility (AMS) to the study of volcanic materials from the Late Carboniferous-Permian Cadí basin (southern Pyrenees) in order to (i) explore the limits of this technique in ancient volcanic materials that have undergone strong chemical alteration and a complex tectonic evolution and (ii) provide new insights on the deposition of volcanic materials in this tectonically controlled sedimentary basin. To establish a comparison with the petrofabric of rocks, AMS was complemented with observations and orientation analyses at the outcrop scale, in oriented polished blocks and in thin sections under the microscope. High resolution sampling (620 specimens from 56 sites located in five transects along a sequence 150 m thick) allowed to characterize the volcaniclastic and lava flow series. The AMS results show a fairly constant average magnetic lineation oriented WNW-ESE (in situ and tilt-corrected) and two secondary maxima (N-S to NE-SW in some areas). The magnetic mineralogy analyses indicate the contribution of paramagnetic and ferromagnetic (magnetite, Tc 580 °C) phases to susceptibility. The magnetic fabric has a close relationship with the spatial distribution and orientation of the mineral and grain components of the studied rocks, mainly controlled by depositional processes, with a negligible contribution of the tectonic imprint. Therefore, the magnetic lineation (i.e. K1 axes) can be reliably used as a paleoflow indicator. Nevertheless, it was not possible to establish a clear correspondence between lithological and magnetic fabric types. The results obtained indicate that the AMS approach represents a powerful tool to infer the paleoflow pattern in ancient volcanic and volcaniclastic rocks, even under a priori unfavourable conditions

Axial longitudinal flow in volcanic materials of the late carboniferous-permian Cadí basin (Southern Pyrenees) determined from anisotropy of magnetic susceptibility

The aim of this work is the application of the anisotropy of magnetic susceptibility (AMS) to the study of volcanic materials from the Late Carboniferous-Permian Cadí basin (southern Pyrenees) in order to (i) explore the limits of this technique in ancient volcanic materials that have undergone strong chemical alteration and a complex tectonic evolution and (ii) provide new insights on the deposition of volcanic materials in this tectonically controlled sedimentary basin. To establish a comparison with the petrofabric of rocks, AMS was complemented with observations and orientation analyses at the outcrop scale, in oriented polished blocks and in thin sections under the microscope. High resolution sampling (620 specimens from 56 sites located in five transects along a sequence 150 m thick) allowed to characterize the volcaniclastic and lava flow series. The AMS results show a fairly constant average magnetic lineation oriented WNW-ESE (in situ and tilt-corrected) and two secondary maxima (N-S to NE-SW in some areas). The magnetic mineralogy analyses indicate the contribution of paramagnetic and ferromagnetic (magnetite, Tc 580 °C) phases to susceptibility. The magnetic fabric has a close relationship with the spatial distribution and orientation of the mineral and grain components of the studied rocks, mainly controlled by depositional processes, with a negligible contribution of the tectonic imprint. Therefore, the magnetic lineation (i.e. K1 axes) can be reliably used as a paleoflow indicator. Nevertheless, it was not possible to establish a clear correspondence between lithological and magnetic fabric types. The results obtained indicate that the AMS approach represents a powerful tool to infer the paleoflow pattern in ancient volcanic and volcaniclastic rocks, even under a priori unfavourable condition

Geology of the Late Carboniferous, Permian and Early Triassic basins of the Eastern Pyrenees

ABSTRACTWe present a detailed geological map of the Upper Carboniferous, Permian and Triassic rocks of the southern border of the Axial Zone in the Eastern Pyrenees. These units were deposited in three intra-mountain, terrestrial basins, characterized by the emplacement/deposition of volcanic, sub-volcanic and volcaniclastic units (ca. 1000 m thick) together with continental red beds. The map is based on unpublished drafts, sketches and structural data. This previous information was complemented with new structural, petrologic and stratigraphic data. The geological map is presented together with three cross-sections, a detailed lithological description, and a stratigraphic correlation panel to help understand the stratigraphy, volcanism and structure and, ultimately, the geometry and origin of the highly subsident areas of this segment of the chain in post-Variscan times. The geological map gives new clues for reconstructing the geometry of these basins and the distribution of the volcanic episodes during the Late Carboniferous and Permian

Geology of the Late Carboniferous, Permian and Early Triassic basins of the Eastern Pyrenees

We present a detailed geological map of the Upper Carboniferous, Permian and Triassic rocks of the southern border of the Axial Zone in the Eastern Pyrenees. These units were deposited in three intra-mountain, terrestrial basins, characterized by the emplacement/deposition of volcanic, sub-volcanic and volcaniclastic units (ca. 1000 m thick) together with continental red beds. The map is based on unpublished drafts, sketches and structural data. This previous information was complemented with new structural, petrologic and stratigraphic data. The geological map is presented together with three cross-sections, a detailed lithological description, and a stratigraphic correlation panel to help understand the stratigraphy, volcanism and structure and, ultimately, the geometry and origin of the highly subsident areas of this segment of the chain in post-Variscan times. The geological map gives new clues for reconstructing the geometry of these basins and the distribution of the volcanic episodes during the Late Carboniferous and Permian.</p

Paleomagnetic study of Late-Carboniferous-Permian rocks from the Cadí Basin (Eastern Pyrenees): Tectonic implications

We have carried out a detailed paleomagnetic study of volcanic rocks (18 sites) and red beds (10 sites) from the Late-Carboniferous-Permian series of the Cadí Basin (Eastern Pyrenees). The study provides reliable Late Carboniferous-Permian paleomagnetic directions, in an area where paleomagnetic studies are scarce. The main characteristic component in both rock types shows a SSE direction with a shallow inclination and a dominant reverse polarity. The magnetic carriers, both in the volcanic rocks and the red beds, are magnetite and hematite. The main component is interpreted as a primary magnetization of Permian age in the red beds; in the Late Carboniferous volcanic rocks, the main component likely represents primary magnetization or early remagnetization. These results are consistent with the poles for the Iberian plate during the Permian and indicate an absence of regional vertical axis rotations for the Orri nappe, in whose hanging wall the Cadí Basin was transported southwards during the Pyrenean orogeny