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Geologische Rundschau

, Volume 82, Issue 3, pp 440–447 | Cite as

Tectonics of the Beja-Acebuches Ophiolite: a major suture in the Iberian Variscan Foldbelt

  • P. Fonseca
  • A. Ribeiro
Article

Abstract

The Beja-Acebuches Ophiolitic Complex (BAOC) (south Portugal/Spain) corresponds to a high grade metamorphic belt along the boundary between Ossa-Morena and the South Portuguese Zones and comprises a lithostratigraphic sequence including (from top to bottom) metabasalts, (metamorphosed) multiple dyke intrusions in gabbro, flasergabbros and metaserpentinites. It is affected by three deformation phases. D1 affects the ophiolite lower stratigraphic units and is represented by a mylonitic cleavage with a stretching lineation where shear criteria indicates the sense of shear to be towards the north-north-east; this deformation event can be related to the ophiolite emplacement above the crystalline footwall of the Serpa antiform, affecting Precambrian basement and Cambrian cover rocks. The obduction polarity ist north-eastwards, similar to the subduction polarity that generates the Beja Gabbroic Complex (BGC), implying a flake geometry. The second deformation phase, D2, is represented by an intense WNW-ESE sinistral shear event which is responsible for the shattered appearance of the suture; D2 is reactivated later by a more brittle D3 event involving thrusting to the south-west, again with a sinistral component. 40Ar/39Ar isotopic ages were obtained for (metamorphosed) multiple dyke intrusions in the BAOC's gabbro (342.6 ± 1.4 Ma), for metagabbroic cumulates (340.7 ± 1.9 Ma), and for the undeformed/unmetamorphosed BGC (341.1 ± 1.3 Ma) occurring to the north of the ophiolitic suture. These ages reflect a last regional cooling event in the area which post-dates the ophiolite emplacement and the intrusion of the BGC through this oceanic sequence.

Key words

Tectonics Beja-Acebuches Ophiolite Iberian Variscan Foldbelt 

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References

  1. Andrade AS (1972) Problèmes géologiques et métallogéniques de l'Alentejo central (Portugal). Mem Not Publ Mus Lab Mineral Geol Univ Coimbra 73: 66–79Google Scholar
  2. Andrade AS (1979) Aspectos geoquimicos do ofiolitóide de Beja. Comun Serv Geol Portugal LXIV: 39–48Google Scholar
  3. Andrade AS (1983) Contribuition à l'analyse de la suture hercynienne de Beja (Portugal), perspectives métallogéniques. Thése présentée à l'INPL pour l'obtention du grade de Docteure d'Etat dès Sciences Naturelles. INPL, Nancy: 137 ppGoogle Scholar
  4. Andrade AS, Pinto AF, Conde LE (1976) Sur la géologie du Massif de Beja: Observations sur la transversale d'Odivelas. Comun Serv Geol Portugal 60: 171–202Google Scholar
  5. Bard JP (1969) Le métamorphisme régional progressif des Sierras d'Aracena en Andalousie occidentale (Espagne): sa place dans le segment hercynien sud-ibérique. Ph D Thesis Univ Montpellier, USTL: 397 ppGoogle Scholar
  6. Bard J P (1970 Composition of hornblendes formed during the Hercynian) progressive metamorphism of the Aracena Metamorphic Belt (SW Spain). Contrib Mineral Petrol 28: 117–134Google Scholar
  7. Bonhommet N, Perroud H, Desouches V, Ribeiro A (1982) Preliminary results for the Upper Devonian Beja Gabbro, Southern Portugal. EOS 63 (18): 308 ppGoogle Scholar
  8. Buisson G, Leblanc M (1986) Gold bearing listwaenites (carbonatized ultramafic rocks) in ophiolite complexes. In: Gallagner MJ, Ixar RA, Neary CR, Prichard HM, (eds.) Metallogeny of basic and ultrabasic rocks, MJ Gallagher, RA Ixer, CR Neary and HM Prichard Edit., Institution of Mining and Metallurgy, London: 121–132Google Scholar
  9. Buisson G, Leblanc M (1987) Gold in mantle peridotites from Upper Proterozoic ophiolites in Arabia, Mali, and Morocco. Econ Geol 82: 2091–2097Google Scholar
  10. Castro P, Quesada C, Munha J (1987) Metamorphic regime in the Beja-Acebuches Variscan ophiolite (SW Iberia). Extended Abstract in Int. Conf. Tectonothermal evolution of the West African orogens and Circum-Atlantic terrane linkages. IGCP Project 233. Nouakchott (Annual Meeting Mauritiana), December 1987Google Scholar
  11. Crespo Blanc A (1989) Evolution geotectónica del contacto entre la Zona de Ossa-Morena y la Zona Surportuguesa en las Sierras de Aracena y Aroche (Macizo Ib&rico Meridional): un Contacto mayor en la cadena hercinica europea. Ph D Thesis, Departamento de Geología u Minería, Universidad de SevilhaGoogle Scholar
  12. Dallmeyer RD, Fonseca P, Quesada C, Ribeiro A 40Ar/39Ar mineral age constraints to the tectonothermal evolution of the Variscan Suture in SW Iberia, Tectonics. in pressGoogle Scholar
  13. Dewey JF (1976) Ophiolite obduction. Tectonophysics 31: 93–120Google Scholar
  14. Fonseca P (1989) Estudo de um segmento da sutura da Cadeia Varisca Ibérica: Serpa — Pulo do Lobo. MSc Thesis, Departamento de Geologia da Faculdadn Ciências da Universidade de Lisboa, Lisbon 127 ppGoogle Scholar
  15. Fonseca P, Ribeiro A (1990) The tectonics of Beja-Acebuches Ophiolite: A major suture in the Iberian Variscan Fold Belt [abstract]. Palaeozoic Orogens in Central Europe, International Geological Correlation Program, Project 233, Terranes in the Circum-Atlantic Palaeozoic Orogens. Göttingen, 4 ppGoogle Scholar
  16. Fonseca P, Dallmeyer RD, Ribeiro A, Quesada C (1990) Tectonothermal evolution of the Beja-Acebuches Ophiolite: Field characteristics and 40Ar/39Ar mineral age constraints [abstract]. Palaeozoic Orogens in Central Europe, International Geological Correlation Program, Project 233, Terranes in the Circum-Atlantic Palaeozoic Orogens, Göttingen - Giessen, August–September 1990, 4 pp (Abstract)Google Scholar
  17. Julivert M, Fontboté JM, Ribeiro A, Conde L (1974) Mapa Tectonnco de la Península Ibérica y Baleares. Escala 1 :1000000, IGME: 10 ppGoogle Scholar
  18. Keppie JD Dallmeyer RD (1989) Tectonic map of Pre-Mesozoic terranes in Circum-Atlantic Phanerozoic orogens. Scale 1: 5000000, IGCP Project No 233, Halifax, CanadaGoogle Scholar
  19. Mata J, Munha J (1985) Geochemistry of mafic metavolcanic rocks from the Estremoz region (South-central Portugal). Comun Serv Geol Portugal 71: 175–185Google Scholar
  20. Mata J, Munhá J Magmatogénese de metavulcanitos Cambricos do Nordeste Alentejano: os estágios iniciais de “rifting” continental. Comun Serv Geol Portugal Vol 76: 45–73Google Scholar
  21. Matte P (1986) Tectonics and plate tectonics models for the variscan Belt of Europe. Tectonophysics 126: 329–374CrossRefGoogle Scholar
  22. Munhá J, Oliveira J, Ribeiro A, Oliveira V, Quesada C, Kerrich R (1986) Beja-Acebuches Ophiolite: characterization and geodynamic significance [abstract]. Maleo Bd Inf Soc Geol de Portugal, vol 2, no 13, p 31Google Scholar
  23. Munhá J, Oliveira J, Ribeiro A, Quesada C, Fonseca P, Castro P (1989) Accreted terranes in southern Iberia: the Beja-Acebuches Ophiolite and Related Oceanic Sequences; 28th International Geological Congress, Washington DC (Abstract) 2, pp 481–482Google Scholar
  24. Quesada, C (1990) Precambrian successions in SW Iberia: their relationship to ‘Cadomian’ orogenic events. The Cadomian Orogeny. Geological Society of London Special Publication No 51: 353–362Google Scholar
  25. Quesada C (1991) Geological constrains on the Palaeozoic tectonic evolution of tectonostratigraphic terranes in the Iberian Massif. Tectonophysics 185: 225–245Google Scholar
  26. Quesada C, Fonseca P, Munha J, Ribeiro A, Oliveira J The Beja-Acebuches Ophiolite (Southern Iberian Variscan Fold Belt): geological characterisation and geodynamic significance, Geodyn. ActaGoogle Scholar
  27. Ribeiro A, Quesada C, Dallmeyer RD (1987) Tectonoestratigraphic terranes and the geodynamic evolution of the Iberian Variscan Fold Belt [abstract]. In: Conference on Deformation and Plate Tectonics Gijón (Spain), Abstract vol. pp 60–61Google Scholar
  28. Ribeiro A, Silva J, Dias R, Araújo A, Marques F, Merino H, Fonseca P (1989) Terranes in the Variscan Fold Belt in Portugal (IGCP Project 233) [abstract]. Tectonothermal Expression of Terrane Accretion Within the Appalachian Orogen. International Geological Correlation Program, Project 233, Terranes in the Circum-Atlantic Palaeozoic Orogens. Athens Georgia (USA), Abstract, 2 ppGoogle Scholar
  29. Ribeiro A, Quesada C, Dallmeyer RD (1990) Geodynamic evolution of the Iberian Massif. In: Dallmeyer RD, Martinez E (eds.) Pre-Mesozoic Geology of Iberia, Springer, Berlin Heidelberg New York Spec Iss, pp 397–410Google Scholar
  30. Santos JF (1990) Petrologia do sector ocidental da Unidade de Odivelas (Maciço de Beja). M Sc Thesis, University of Aveiro: 226 ppGoogle Scholar
  31. Santos JF, Mata J, Gonqalves F, Munhá J (1985) Hercynian magmatism in the Santa Suzana region (Alcácer do Sal, South Portugal): identification of a carboniferous convergent plate margin in the southern branch of the Iberian Hercynian Chaine. VIII Reuniao do Grupo de Ossa Morena, Lisbon (Villafranca de Las Barros), Instituto de Geologia Economica, Universidad Complutense Madrid, pp 16–17Google Scholar
  32. Santos JF, Mata J, Gonçalves F, Munhá J (1987) Contribuição para o conhecimento geológico-petrolóco da região de Sta Suzana: o Complexo Vulcano-Sedimentar da Toca da Moura. Com Serv Geol, 73, Fasc 1/2: pp 29–48 PortugalGoogle Scholar

Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • P. Fonseca
    • 1
  • A. Ribeiro
    • 1
  1. 1.Departamento de Geologia da Faculdade de Ciências da Universidade de LisboaLisbonPortugal

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