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EIL-10 Large-scale seismic transects: Images of the Earth?s crust and mantle
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New constraints on crustal structure of the southern Iberian Variscaides from deep seismic reflection profiles (IBERSEIS, ALCUDIA Projects)
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Ramon Carbonell, CSIC-Institute of Earth Sciences (Spain)
Fernando Simancas, University of Granada (Spain)
David Martínez-Poyatos, University of Granada (Spain)
Puy Ayarza, University of Salamanca (Spain)
Imma Palomeras, CSIC-Institute of Earth Sciences (Spain)
Antonio Jabaloy, University of Granada (Spain)
Pablo Gonzalez, University of León (Spain)
Rosa Tejero, Universidad Complutense de Madrid (Spain)
Jeronimo Matas, Instituto Geológico y Minero de España (Spain)
Luís Martín-Parra, Instituto Geológico y Minero de España (Spain)
Antonio Azor, University of Granada (Spain)
Francisco González-Lodeiro, University of Granada (Spain)
Luís García-Lobón, Instituto Geológico y Minero de España (Spain)
Andrés Pérez-Estaún, CSIC-Institute of Earth Sciences "Jaume Almera" (Spain)
Luís Mansilla, Escuela Politécnica Universitária de Almadén (Spain)
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The IBERSEIS and ALCUDIA projects acquired two deep seismic reflection transects across the Variscan Orogen of southwestern Iberia. Jointly both transects complete almost 600 km of deep seismic reflection data, crossing the southern half of the Iberian Variscides and it offers a unique opportunity to study transpression tectonics. It extends from the Tajo basin southward till Gulf of Cadiz.
The 20 s (twtt), deep seismic reflection image provides key constraints in the crustal structure of the southwestern Iberian. The seismic profile crosses key elements of the Variscan Orogen, runs across major tectonic units including the South Portuguese Zone (SPZ), Ossa Morena Zone (OMZ) and a large percentage of the Central Iberian Zone. Cutting across two major suture zones and some major geological structures and domains, with the Iberian Pyrite Belt being of the greatest interest, the Pulo do Lobo Unit, the Aracena metamophic belt, the Central Unit, the Santa Elena fault, the Almadén syncline, the Alcudia anticline, and the Toledo fault, and some major magnetic anomalies. The preliminary results reveal that the crust is 30 km thick in average,in both profiles, with a horizontal Moho, a highly reflective mid-to-lower crust with a few mantle reflectors and well defined features in the upper crust with the indication of detachments zones that might link to the mid-crustal reflective zone. The main scientific results address:
a) the characterization of the seismic facies of the SW Iberian lithosphere, with a view to differentiate crustal and lithospheric domains;
b) the architecture of the major tectonic contacts;
c) the deep geometry of the transpression tectonics located in specific areas. The seismic data reveals the existence of a mid-crustal reflective body (IRB) located within the OMZ. This 140 km long and up to 5 km thick high amplitude reflective band cuts across the sutures that limit the OMZ.
The amplitude characteristics of the seismics, mineralization studies related to magmatic ore deposits, and the surface geology suggest that the IRB is a mantle-derived mafic intrusion. The geophysical, geological and petrological data suggest that the IRB is most probably an Early Carboniferous (approximately at 350-340 Ma) mantle-derived intrusion possibly linked to plume activity that took place in Europe in the Carboniferous and Permian. South of the CIZ the image reveals a sudden change in the seismic fabric indicating the acreation of two different continental crusts.
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