The Iberian Massif (IM) in the western half of Iberian Peninsula represents the largest and one of the most complete and continuous exposures of Variscan Belt in Western Europe (Figure 1). The arcuate shape of Variscan Belt in Western Europe result from a continent-continent collision between an Ibero-Aquitanian indentor (western Gondwana) (Matte and Ribeiro, 1975; Dias and Ribeiro, 1995; Brun and Burg, 1982; Matte, 1986; Burg et al., 1987) and a northern continent (Báltica? - N. America) (Ribeiro et al., 1990; Quesada et al., 1994). This process is responsible for the formation of the Ibero-Armorican arc by differential collision, which has produced crustal imbrication in frontal areas, left-lateral transpression in Iberia and right-lateral transpression in Armorica. It has been proposed (Crespo Blanc and Orozco, 1988; Fonseca, 1995; Fonseca et al., 1999) that a major ocean (Rheic ocean) was closed by subduction/obduction towards the inner part of the arc, leaving some remainder ophiolitic slices: the Lizard suture in SW England and the Beja Acebuches suture zone, respectively in the northern and southern branches of the Ibero Armorican Arc.
Figure 1. Tectonostratigraphic Terrane Map
Tectonostratigraphic Terrane Map of the Iberian Massif and geological map of the southern portuguese sector of the Iberian Massif (adapted from the Geological Survey map of Portugal, 1/500.000 scale).
The IM represents the ancient substratum of the Iberian Peninsula. It covers one third of the emerge territory of Iberia and supposed be stable since late Palaeozoic ages. It has been subdivided in several zones (Chacón et al., 1983; Julivert & Martinez, 1983; Julivert et al., 1974; Lotze, 1945) and one of these zones is the Ossa Morena Zone (OMZ). The IM has been considered peripheral to Gondwana, during almost all of the Palaeozoic, located very near the boundary of this continent to Laurentia (San José et al., 2004). The final result is due to the amalgamation of several tectonic terranes one of them the OMZ (Keppie & Dallmeyer, 1989). The connections between these tectonic terranes sometimes were very well expressed, underlined by suture zones with oceanic affinities like in other orogenic belts (Coney et al., 1980; Dewey & Birth 1970; 1971; Keppie & Dallmeyer, 1989. The Beja-Acebuches Ophiolitic Complex (BAOC) represents the Variscan suture in southwest of Iberia Peninsula, accreted to the OMZ substratum (Fonseca and Ribeiro, 1993; Fonseca et al. 1999; Fonseca, 1995). The BAOC separates the OMZ and the South-Portuguese Zone (SPZ – comprising Iberian Pyrite Belt and Pulo do Lobo Sequence), which is regarded as an exotic terrane originated from south and accreted, to Iberian Autochthon, during the Carboniferous times. Recently new dismembered ophiolitic slices have been found in the OMZ (Internal Ossa-Morena Zone Ophiolitic Sequences – IOMZOS), witch corresponds to allochthonous klippen on top of lower Palaeozoic sequences (Araújo et al. 1993; Fonseca, 1995; Pedro, 2004).
The Guadiana River is nearly perpendicular to the variscan structures and represents the best transverse, crossing the south variscan fold belt in Portugal (Figure 1). In fact, the well-exposed outcrops in this valley allow detailed structural mapping and, during the last years, several PhD theses on structural geology were achieved, enclosing distinct sectors of the Guadiana Valley, in Ossa-Morena and South Portuguese Zones (Silva 1989; Araújo, 1995; Fonseca, 1995; Piçarra 2000; Borrego in prep.)
The aim of this work is (1) to present unpublished geological mapping, (2) to make a review of the geometrical and kinematical structural data and (3) to make a global interpretation of a segment of the Guadiana Valley, covered by three contiguous PhD theses (Araújo, 1995; Fonseca, 1995; Borrego in prep.). Finally, we propose a general interpretation of the structure, on the basis of a geological cross section, from the suture zone to the central sector of the Ossa-Morena Zone.