Geology, geomorphology and stratigraphy from Carvoeiro-Caldas de S. Jorge and Soutelo-Arrancada do Vouga structural domains (Porto-Coimbra-Tomar shear zone, NW Portugal): Tectonostratigraphic implications [Geologia, geomorfologia e estratigrafia dos domínios estruturais de Carvoeiro-Caldas de S. Jorge e de Soutelo-Arrancada do Vouga (faixa de cisalhamento de Porto-Coimbra-Tomar, NW de Portugal): implicaç ões tectonoestratigráficas]

• Type: Article in International Scientific Journal
• Date: 2004

Authors

Chamine, HelderI (Author) Other; Gomes, Aant�nio Alberto (Author) FLUP; Teixeira, Jos� (Author) Other; Fonseca, P.E. (Author) Other; Jesus, A. Pinto de (Author) Other; Pereira, L.C. Gama (Author) Other; Andrade, A.A. Soares de (Author) Other; Fernandes, J.P. (Author) Other; Moco, L.P. (Author) Other; Flores, Deolinda (Author) FCUP; Ara�jo, Maria da Assun��o (Author) FLUP; Rocha, F.T. (Author) Other

Journal

Title: Cadernos do Laboratorio Xeoloxico de Laxe

Pages: 299-330

ISSN: 0213-4497

Publisher: Seminario de Estudos Galegos

Indexing

ISI Web of Knowledge

Scopus - 3 Citations

Other information

Authenticus ID: P-007-SHS

Abstract (EN): The aim of this study is to characterise the regional tectonostratigraphy, geomorphology and geological mapping of the structural domains Caldas de S. Jorge-Carvoeiro and Soutelo-Arrancada do Vouga (NW of Portugal). These domains take the form of a narrow N-S strip of the Lower Palaeozoic age, which is included in a major crustal-scale shear zone, the Porto-Coimbra-Tomar-Ferreira do Alentejo shear zone. This is a dextral transcurrent mega-structure belonging to the Iberian Variscan belt (Portugal). The tectonostratigraphic units (mainly formed by metasedimentary and blastomylonitic rocks) cropping out in this domain are delimited, at W and E, by dextral wrench-faults constituing the Porto-Albergaria-a-Velha-Coimbra shear zone (s.str.). Until very recently, the studies carried out in the Caldas de S. Jorge-Carvoeiro-Arrancada do Vouga Palaeozoic structure considered most of its metasedimentary outcrops as belonging to the "Complexo Xisto-Grauváquico" (Late Proterozoic). Actually, however, geological field studies developed in this area pointed out the need for a tectonostratigraphic revision. As a result of this revision, new stratigraphic units were described as follows in the structural domains referred: i) Caldas de S. Jorge and Arrancada do Vouga Units, constituted by massive quartzites and sandstones containing rounded pebbles of quartzite and quartz. The massive quartzite rocks are intensely deformed (milonitic fabrics, shearing folds, marked stretching lineation, pseudotachylyte bands); quartzite bands become less common and thinner towards the top. Caldas de S. Jorge Unit is, in part, equivalent to the Armorican Quartzite, which occurs in several areas of the Iberian Massif and is mainly considered as of Arenigian age. Locally, this unit is correlated to part of the Armorican Quartzite Fm., from Buçaco region, and to Santa justa Fm., from Valongo region; ii) Carvoeiro and Veiga Units, a monotonous sequence of cleaved dark grey mudstones with macrofossils at relatively restricted horizons. The Carvoeiro Unit is equivalent to part of Valongo Fm. and of Fonte da Horta Fm. (Cácemes Group, Buçaco region). The fossil record from Carvoeiro Unit suggests a Llandeilian-Llanvirnian age, in good agreement with the classic Lower Palaeozoic sequences of the Central-Iberian Zone. The highly deformed and rare macrofossils recently found in Mouquim-Carvoeiro area comprise brachiopods (Orthis noctilio Sh.), already identified by J. F. Nery Delgado (1908), and trilobites (CALYMENIDEA?) and echinoderms (CYSTOIDEA?), newly described in this region. This record suggests a Llandeilian-Llanvirnian age for this unit. A micropalaeontological study was also attempted. Microfossils are, usually, badly preserved and not quite abundant. Acritarchs are recognised, although their degree of preservation prevents further identification. The presence of chitinozoans, also badly preserved and generally broken, could nevertheless be ascertained. Organic petrology results show a very poor organic content. The organic particles are thermally altered and its classification resulting very difficult. They can be classified as "vitrinite-like" organoclasts, and sometimes show their vegetal origin (preservation of tissue morphology). The coalification degree is always very high, corresponding to the upper epizone (low-metamorphism) the particles being assumed as semi-graphite. The clay mineralogy and geochemistry characterisation are in good agreement with the organic petrology data. Geodynamic implications for the Iberian Variscides of the Palaeozoic basement framework are discussed. Further research is been carried on in order to find out other evidences of this Lower Palaeozoic structure along the Porto-Coimbra-Tomar shear zone (s.str.). In addition, further tectonostratigraphic, biostratigraphic, organic petrology and clay mineralogy research is currently in progress, to improve our knowledge on Caldas de S. Jorge-Carvoeiro and Soutelo-Arrancada do Vouga (Águeda) structural domains.

Language: Portuguese

Type (Professor's evaluation): Scientific

No. of pages: 32