Discursos pronunciados en el acto de investidura de Doctora "Honoris Causa" de la Excelentísima Señora Dª Aziza Bennani

Presentado por el Doctor Don Francisco González Lodeir

Reorganization of Northern Peri-Gondwanan Terranes at Cambrian–Ordovician Times: Insights from the Detrital Zircon Record of the Ossa-Morena Zone (SW Iberian Massif)

The Ossa-Morena Zone constitutes a fringe Gondwana-related terrane all along the Paleozoic. This continental block has been classically interpreted as being attached to a portion of the northern Gondwanan margin located close to the West African Craton. We report here the results of U-Pb dating on detrital zircon grains from 15 metasedimentary rocks collected in two well-exposed and well-dated Cambrian sections (Córdoba and Zafra) of the Ossa-Morena Zone. The studied samples show a dominant late Tonian-Ediacaran population peaked at c. 600 Ma. Secondary populations are Rhyacian-early Orosirian and late Orosirian-Statherian in age, with maxima at c. 2.1 and 1.9 Ga. Minor detrital zircon populations are Mesoarchean-early Siderian in age, with peaks between c. 3.05 and 2.45 Ga. Most of the studied samples lack a Stenian-early Tonian population, except for two of them with a minor peak at c. 1 Ga. Our results corroborate previous studies that locate the Ossa-Morena Zone close to the West African Craton and/or the Tuareg Shield (i.e., in a western position with respect to other Variscan zones of the Iberian Massif) at the onset of the rifting stage that opened the Rheic Ocean. Nevertheless, the absence of a significant Stenian-early Tonian population in the Cambrian Ossa-Morena rocks contrasts with the reported results on middle Ordovician-Lower Devonian rocks of this zone, which systematically contain an important population with a peak at c. 1 Ga. We relate this change to the latest Ediacaran-early Ordovician paleogeographic/paleotectonic evolution of the Ossa-Morena Zone, which might have recorded a significant eastward displacement, together with a reorganization of the drainage systems. Thus, the vanishing stages of the Cadomian orogeny could have translated eastward the Ossa-Morena Zone terrane at latest Ediacaran-earliest Cambrian time due to change in plate kinematics from subduction to right-lateral shearing. This translation would have shifted the Ossa-Morena Zone from an Ediacaran location close to the West African Craton to a Cambrian position close to the Tuareg Shield. Finally, the rift-to-drift transition occurred at late Cambrian-early Ordovician time along the northern Gondwanan margin would have reorganized the drainage systems, facilitating sediment supply from an eastern source with abundant Stenian-early Tonian detrital zircon grains, probably the Saharan Metacraton.Consejeria de Transformacion Economica, Industria, Conocimiento y Universidades de la Junta de Andalucia P20_00063 PY20-01387Ministry of Science and Innovation, Spain (MICINN) Spanish Government PID2020-118822GB-I00 PID2020-119651RB-I0

Comparación del Neoproterozoico/Paleozoico inferior de Marruecos y del SO de Iberia. Interpretaciones geodinámicas

El Neoproterozoico del sudoeste de Iberia (Serie Negra y Formación Malcocinado) es contemporáneo de un magmatismo calcoalcalino (Precámbrico PIII del Anti-Atlas de Marruecos) que sella la Orogenia Cadomiense. El Cámbrico inferior y medio está representado, tanto en Iberia como en Marruecos, por secuencias detríticas y vulcanosedimentarias formadas en un contexto de rifting. Sin embargo, la evolución de estas dos regiones se diferenció a partir del Cámbrico superior: en el sudoeste de Iberia, la actividad extensional continuó durante el Ordovícico, desarrollándose dominios oceánicos; en Marruecos, dominó durante el resto del Paleozoico inferior un régimen de plataforma débilmente extensiona

Crustal Imbrication in an Alpine Intraplate Mountain Range: A Wide-Angle Cross-Section Across the Spanish-Portuguese Central System

Intraplate ranges are topographic features that can occur far from plate boundaries, the expected position of orogens as described in the plate tectonics theory. To understand the lithospheric structure of intraplate ranges, we focused on the Spanish-Portuguese Central System (SPCS), the most outstanding topographic feature in the central Iberian Peninsula. The SPCS is an Alpine range that exhumes Precambrian-Paleozoic rocks and is located at >200 km from the northern border of the Iberian microplate. Here, we provide a P-wave velocity model based on wide-angle seismic reflection/refraction data of the central SPCS (Gredos sector). Our results show: (a) a layered lithosphere characterized by three major interfaces: Conrad, Mohorovicic, and Hales discontinuities, (b) an asymmetry of the crust-mantle boundary under the SPCS, (c) the extent of the Variscan batholith forming the main outcrops of Gredos, and (d) the thinning of the lower crust toward the south. This model suggests that the exhumation of the SPCS basement was driven by a south-vergent thick-skinned thrust system, developed in the southern part of the SPCS and that promoted crustal imbrication and a Mohorovicic discontinuity's offset under the SPCS. Thus, the deformation mechanisms of the crust seem to be controlled by the presence of the late- to post-Variscan granitoids that assimilated the Variscan mid-crustal detachment creating a new rheological boundary. This tectonic structure allowed the formation of Alpine crustal-scale thrust systems that eased coupled deformation of the upper and lower crust, leading to limited underthrusting of both crustal layers.Ministry of Science, Innovation and Competitiveness through the Project CIMDEF (CGL2014-56548-P)Spanish Government and the University of Salamanca (Beatriz Galindo grant BEGAL 18/00090)Grant IJC2018-036074-I, funded by MCIN/AEI/10.13039/501100011033Grants CGL2015-71692 (MINECO/ FEDER) and PID2020-118822GB-I00 (MCIN/AEI/10.13039501100011033

Crustal Imbrication in an Alpine Intraplate Mountain Range: A Wide-Angle Cross-Section Across the Spanish-Portuguese Central System

Intraplate ranges are topographic features that can occur far from plate boundaries, the expected position of orogens as described in the plate tectonics theory. To understand the lithospheric structure of intraplate ranges, we focused on the Spanish-Portuguese Central System (SPCS), the most outstanding topographic feature in the central Iberian Peninsula. The SPCS is an Alpine range that exhumes Precambrian-Paleozoic rocks and is located at >200 km from the northern border of the Iberian microplate. Here, we provide a P-wave velocity model based on wide-angle seismic reflection/refraction data of the central SPCS (Gredos sector). Our results show: (a) a layered lithosphere characterized by three major interfaces: Conrad, Mohorovicic, and Hales discontinuities, (b) an asymmetry of the crust-mantle boundary under the SPCS, (c) the extent of the Variscan batholith forming the main outcrops of Gredos, and (d) the thinning of the lower crust toward the south. This model suggests that the exhumation of the SPCS basement was driven by a south-vergent thick-skinned thrust system, developed in the southern part of the SPCS and that promoted crustal imbrication and a Mohorovicic discontinuity's offset under the SPCS. Thus, the deformation mechanisms of the crust seem to be controlled by the presence of the late- to post-Variscan granitoids that assimilated the Variscan mid-crustal detachment creating a new rheological boundary. This tectonic structure allowed the formation of Alpine crustal-scale thrust systems that eased coupled deformation of the upper and lower crust, leading to limited underthrusting of both crustal layers.This study has been funded by the Ministry of Science, Innovation and Competitiveness through the Project CIMDEF (CGL2014-56548-P). IP is funded by the Spanish Government and the University of Salamanca (Beatriz Galindo grant BEGAL 18/00090). JA is funded by grant IJC2018-036074-I, funded by MCIN/AEI/10.13039/501100011033. DMP and FGL are also funded by grants CGL2015-71692 (MINECO/ FEDER) and PID2020-118822GB-I00 (MCIN/AEI/10.13039/501100011033).Peer reviewe