Tectonostratigraphy of the Porto-Albergaria-a-Velha-Coimbra-Tomar Shear Zone between Central-Iberian and Ossa-Morena Zones (Iberian Massif, W Portugal) [Tectonoestratigrafia da faixa de cisalhamento de Porto-Albergaria-a-Velha-Coimbra-Tomar, entre as Zonas Centro-Ib¿erica e de Ossa-Morena (Maci¿co Ib¿erico, W de Portugal)]

• Type: Article in International Scientific Journal
• Date: 2003

Authors

Chamine, HI (Author) Other; Gama Pereira, LC (Author) Other; Fonseca, PE (Author) Other; Noronha, F (Author) FCUP; de Sousa Lemos, MJ (Author) Other

Journal

Title: Cadernos do Laboratorio Xeoloxico de Laxe

Pages: 37-78

ISSN: 0213-4497

Publisher: Seminario de Estudos Galegos

Indexing

ISI Web of Knowledge

Scopus - 21 Citations

Other information

Authenticus ID: P-007-BM3

Abstract (EN): The NW border of the Iberian Massif is transected by a dextral wrench-fault, the Porto-Coimbra-Tomar shear zone (W Portugal). This major fault constitutes the boundary between the Ossa-Morena Zone (OMZ), in the west block, and the Central-Iberian Zone (Iberian Variscan Chain), in the east block. This tectonometamorphic belt comprises middle/upper Proterozoic and upper Palaeozoic units. To help clarify the complex geodynamic evolution of this major shear zone, we carried out stratigraphic and tectonic studies on the Foz do Douro (Porto)-Espinho-Coimbra-Tomar substrate (OMZ). We first performed a multidisciplinary study comprising systematic and detailed mapping of the region, as well as detailed characterisation of the tectonostratigraphic framework. In a subsequent stage, critical outcrops were selected for specific studies, namely meso- and microtectonic studies, in addition to structural petrology and geochronology analysis. Our results indicate that on the western border of the Porto-Tomar shear zone, a complex tectonic imbrication occurs which provides out-of-sequence tectonostratigraphic units with an unusual character and contrasting metamorphic features. Indeed, tectonical, petrological and palynological evidences from Albergaria-a-Velha-Coimbra-Espinhal revealed, for the very first time in this OMZ sector, an imbrication of black shales from the upper Palaeozoic (late Devonian to early Carboniferous ages) into upper Proterozoic garnetiferous phyllites and micaschists. Litho-tectonic and palaeontological similarities between OMZ borders in the northern (Porto-Tomar region, W Portugal) and southern branchs (Vendas Novas-Ferreira do Alentejo, SW Portugal) led us to infer that the Porto-Tomar shear zone extends itself to the south of Tomar, as far as Ferreira do Alentejo, constituting the Porto-Tomar-Ferreira do Alentejo major shear zone. This shear zone would correspond to the oldest and most important tectonic structure in the Iberian Massif. Furthermore, this shear zone would have been active since the early phases of the Variscan orogeny and, probably, during the whole Variscan Wilson cycle. This collisional oblique frontier corresponds to a transcurrent fault characteristic of an interplate background, in an oblique convergent plate boundary scenario. The geotectonic situation of Porto-Tomar-Ferreira do Alentejo and Tomar-Badajoz-¿ordoba shear zones is closely similar to that of the San Andreas fault zone in California (U.S.A.).

Language: Spanish

Type (Professor's evaluation): Scientific