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Geological Society, London, Memoirs; 2006; v. 32; p. 345-354;
DOI: 10.1144/GSL.MEM.2006.032.01.21
© 2006 Geological Society of London

Mesozoic-Palaeozoic Europe

Transpressional collision tectonics and mantle plume dynamics: the Variscides of southwestern Iberia

J. F. Simancas1, R. Carbonell2, F. González Lodeiro1, A. Pérez Estaún2, C. Juhlin3, P. Ayarza4, A. Kashubin3, A. Azor1, D. Martínez Poyatos1, R. Sáez5, G. R. Almodóvar5, E. Pascual5, I. Flecha2 & D. Martí2

1 Departamento de Geodinámica, Facultad de Ciencias, Universidad de Granada, Campus de Fuentenueva, 18071 Granada, Spain (simancas{at}ugr.es)
2 Instituto de Ciencias de la Tierra 'Jaume Almera', Consejo Superior de Investigaciones Científicas, c/Lluis Solé i Sabarís s/n, 08028 Barcelona, Spain
3 Department of Earth Sciences, Uppsala University, Villavagen 16, SE-752 36 Uppsala, Sweden
4 Departamento de Geología, Universidad de Salamanca, 37008 Salamanca, Spain
5 Departamento de Geología, Universidad de Huelva, 21071 Huelva, Spain

In southwestern Iberia, three continental domains (the South Portuguese Zone (SPZ), Ossa-Morena Zone (OMZ) and Central Iberian Zone (CIZ) collided in Devonian-Carboniferous time. The collision was transpressional, with left-lateral kinematics, and was interrupted by extensional tectonics during the earliest Carboniferous, when bimodal magmatism (with associated mineral deposits) and basin development were the dominant orogenic features. Transpression was renewed in Visean time, and persisted until the end of the Carboniferous. The IBERSEIS deep seismic reflection profile helps to define the 3D geometry of transpressional structures: out-of-section displacements concentrate in bands, which bound wedges of upper crust; this crustal wedging strongly modifies the geometry of the sutures between continental blocks. A mid-crustal strongly reflective thick band (the Iberseis Reflective Body, IRB) is interpreted as a huge body of basic rocks. The IRB magma trapped in the middle crust was linked to the Early Carboniferous mantle-derived magmatism that crops out in the SPZ, OMZ and CIZ. Magmatism at the surface and trapped in the crust, high thermal gradients and basin development reflect a thermal anomaly in the underlying mantle, influencing both the thermal and the stress state of the orogen at that time. A mantle plume is inferred to have existed in the Early Carboniferous, the transpressional tectonic regime dominating again after its decay.