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Geologische Rundschau

, Volume 76, Issue 1, pp 147–168 | Cite as

Petrogenesis of early paleozoic peralkaline rhyolites from the Macedo de Cavaleiros region (NE Portugal)

  • M. Luisa Ribeiro
Article

Abstract

The petrology and geochemistry of Variscan peralkaline gneisses from NE Portugal, discovered in 1962, is presented. Major and trace element data for the oversaturated sequence of the Macedo de Cavaleiros area depict some specific geochemical patterns: high Fe2O3(t) (even higher than in the Ethiopian Main Rift), high REE concentrations and small Eu anomalies. Field and petrographical observations also suggest that liquid immiscibility has played an important petrogenetic role in the crystallization trends. The alternating pyroxenefeldsparhematite-rich bands observed in outcrop are interpreted as resulting from fluctuating fO2 conditions. Petrological and geochemical data show that these pantelleritic and comenditic rocks are the end members of an alkaline-transitional basaltic sequence, by which they are overlain. An uppermost sequence of oceanic tholeiitic basalts completes the picture of an evolving rift environment, where mantle processes generate crustal thinning and eventually oceanic crust.

Keywords

Oceanic Crust Tholeiitic Basalt Trace Element Data Geochemical Pattern Ethiopian Main Rift 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Zusammenfassung

Petrologie und Geochemie variszischer peralkaliner Gneisse aus Nordostportugal, 1962 entdeckt, werden dargestellt. Die Haupt- und Spurenelementanalysen dieser übersättigen Gesteine weisen Besonderheiten auf, wie z. B. die hohen Fe203-Gehalte, die selbst noch die des »Ethiopian Main Rift« übersteigen, die hohen Konzentrationen an Seltenen Erdelementen und die kleine negative Eu-Anomalie. Geländegeologie und Petrographie suggerieren, da\ die liquid-magmatische Entmischung eine wichtige petrogenetische Rolle im Kristallisationsablauf spielte. Im Aufschlu\ wird eine Wechsellagerung von Pyroxen-Feldspat- und Hämatit-reichen Schichten beobachtet, die hier als Folge von fO2-Schwankungen erklärt wird. Die petrologischen und geochemischen Daten zeigen, da\ die pantelleritischen und comenditischen Gesteine die letzten Glieder in einer Abfolge vom alkalinen übergangstyp darstellen... Die vulkanische Abfolge im Gebiet von Macedo de Cavaleiros endet mit tholeiitischen Basalten, die damit das Bild der magmatischen Entwicklung in einem Rift-Bereich, in dem Mantelprozesse eine Krustenverdünnung in einem Rift-Bereich, in dem Mantelprozesse eine Krustenverdünnung und die Bildung ozeanischer Kruste bewirkten, vervollständigen.

Résumé

L'auteur présente la pétrologie et la géochimie des gneiss varisques peralcalins du nord-est du Portugal, découverts en 1962. Les analyses des éléments majeurs et en traces dans ces roches sursaturées montrent quelques caractéristiques spéciales comme la haute teneur en Fe2O3 (t) (supérieure mÊme à celles de l'»Ethiopian Main Rift«), la haute concentration en terres rares et la faible anomalie négative de Eu. La géologie de terrain et les observations pétrographiques suggèrent aussi que l'imiscibilité entre liquides a joué un rÔle pétrogénétique important au cours de la cristallisation. Les alternances de bandes alternativement riches en pyroxène-feldspath et en hématite, observées sur les affleurements, sont interprétées comme le résultat de la fluctuation de fO2. Les données pétrologiques et géochimiques montrent que les roches pantéléritiques et comenditiques représentent les derniers termes d'une séquence du type alcalintransitionel qui les surmonte. La séquence volcanique dans le secteur de Macedo de Calvaleiros se termine par des basaltes tholéiitiques qui complètent le cadre d'une environnement d'un zone de »rift« dans laquelle les processus mantéliques ont déterminé l'amincissement crustal et la formation d'une croûte océanique.

кРАткОЕ сОДЕРжАНИЕ

пРИВОДьтсь пЕтРОлОг ИЧЕскИЕ И гОЕхИМИЧЕс кИЕ ДАННыЕ ИсслЕДОВАНИь ВАРИсс кИх пЕРЩЕлОЧНых гНЕИ сОВ, РАспРОстРАНЕННых В с ЕВЕРО-ВОстОЧНОИ ЧАст И пОРтУгАлИИ, ОпИсАННыЕ ВпЕРВыЕ В 1962 гОДУ. РАспРЕДЕлЕНИЕ ОсНОВНых И РАссЕьНых ЁлЕМЕНтОВ В ЁтИх пЕРЕ сыЩЕННых пОРОДАх пРОьВльЕт НЕ кИЕ ОсОБЕННОстИ, кАк НАпР.: ВысОкОЕ сОДЕ РжАНИЕ Fe2O3, пРЕВышАУЩЕ Е ДАжЕ тАкОВОЕ В “Ethiopian Main Rift”, В ысОкОЕ сОДЕРжАНИЕ РЕДкИх жЕМЕль И НЕБОл ьшУУ ОтРИцАтЕльНУУ АНОМАлИУ ЕВРОпИь. НА О сНОВАНИИ пОлЕВых И пЕтРОгРАФИЧЕскИх ИсслЕДОВАНИИ УстАНО ВИлИ, ЧтО В хОДЕ кРИстАллИжАцИИ ВАжН УУ пОРОДО-ОБРАжУУЩУУ РОль ИгРАУт пРОцЕссы лИкВ АцИИ. В ОБНАжЕНИьх Уст АНОВИлИ пЕРЕМЕжАУЩЕЕсь жАлЕ гАНИЕ слОЕВ, БОгАтых п ИРОксЕНОМ, пОлЕВыМ шпАтОМ И гЕМА тИтОМ, ЧтО ОБЩьсНьУт кОлЕБАНИьМИ FeO2. пЕтРОл ОгИЧЕскИЕ И гЕОхИМИЧ ЕскИЕ ДАННыЕ УкАжыВАУт НА т О, ЧтО пАНтЕллЕРИтНыЕ И кОМЕНДИтНыЕ пОРОДы пРЕДстАВльУт сОБОИ ж АВЕРшАУЩИЕ ЧлЕНы В РьДУ пОРОД ЩЕл ОЧНОгО пЕРЕхОДНОгО тИпА. ВУлкАНИЧЕскИЕ О тлОжЕНИь В РЕгИОНЕ Macedo de Cavaleiro жАВЕРшАУтсь тОлЕИ тНыМИ БАжАльтАМИ, ЧтО ДОпОлНьЕт кАРтИН У МАгМАтИЧЕскОгО РАжВИтИь В РЕгИОНЕ РИ ФтА, гДЕ пРОцЕссы, пРОт ЕкАУЩИЕ В МАНтИИ, пРИВОДьт к РА жжИжЕНИУ пОРОД МАтЕРИкОВОИ кОРы И ОБ РАжОВАНИУ ОкЕАНИЧЕс кОИ кОРы.

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References

  1. AssunÇāo, C. T. &ConÇalves, F. (1970): ContribuiÇāo para conhecimento das rochas hiperalcalinas e alcalinas (gnaisses hastingsiticos) do Alto Alentejo (Portugal). - Bol. Soc. Geol. Portugal,17, 187–228.Google Scholar
  2. Badham J. P. N.,Williams, J. P. &Wraith, D. (1982): Geochemical characterization of metabasites in N. Portugal and lithogeochemical prospection for Cu-Fe sulphides - (in press).Google Scholar
  3. Bailey, D. K. &MacDonald, R. (1970): Petrochemical variations among middle peralkaline (comendite) obsidians from the oceans and continents. - Contr. Min. Petrology,28, 340–351.Google Scholar
  4. — &Schainer, J. F. (1966): The system Na2O-Al-2O3-Fe2O3-SiO2 at 1 atmosphere, and the petrogenesis of alkaline rocks. - J. Petrology,7, 114–170.Google Scholar
  5. Barbieri, F. Ferrara, Santacroce, G., Treuil, M. R. &Varet, J. (1975): A transitional basalt-pantellerite sequence of fraccional crystallization, the Boina Centre (Afar Rift, Ethiopia). - J. Petrology16, 1, 22–56.Google Scholar
  6. Bard, J. P.,Burg, J. P.,Matte, Ph. &Ribeiro, A. (1980): La chaine hercynienne d'Europe Occidentale en termes de tectonique de plaques. -26, I.G.C., Paris, B.R.G.M. et S.G.N. ed., C6, 233–246.Google Scholar
  7. Bowden, P. (1974): Oversaturated alkaline rocks: granits, pantellerites and comendites. - The Alkaline rocks ed. H. Sorensen. John Wiley & Sons, London, pp. 109–123.Google Scholar
  8. — &Whitley, J. E. (1974): Rare earth patterns in peralkaline and associated granites.- Lithos7, 15–21.Google Scholar
  9. Bowen, N. L. (1945): Phase equilibria bearing on the origin and differentiation of alkaline rocks. - A. J. Sc.,243A, 75–90.Google Scholar
  10. Burri, C. (1928): Zur petrographie der Natronsyenite von Alter Pedroso, und ihrer basischen Differentiate. - Schw. Min. Petr. Mitt.,8, 374–436.Google Scholar
  11. Carmichael, I. S. E. &Mackenzie, W. S. (1963): Feldspar-liquid equilibria in pantellerites: an experimental study. - Am. Journ. Sc.,261, 382–396.Google Scholar
  12. — &Nicholls, J. (1967): Iron-Titanium oxydes and oxygen fugacities in volcanic rocks. - Journ. Geog.,72, 4665–4687.Google Scholar
  13. Casqero, J. L. G., Boelrijk, N. A. I. M., Chacon, J. &Priem, H. N. A. (1985): Rb-Sr evidence for the presence of Ordovician granites in the deformed basement of the Badajoz-Cordova belt, SW Spain. - Geol. Rundschau, 74/2, 379–384, Stuttgart.Google Scholar
  14. Coombs, D. S. (1963): Trends and affinities of basaltic magmas and pyroxenes as illustrated on the diopside-olivina-silica diagram. - Min. Soc. Am. Spec. Pap.1, 227–250.Google Scholar
  15. Drexler, J. W., Bornhorst, T. J. &Noble, D. C. (1983): Trace-elements sanidina-glass distribution coefficients for peralkaline silicic rocks and their implications to peralkaline petrogenesis. - Lithos,16, 265–271.Google Scholar
  16. Floor, P. (1966): Petrology of an aegirine-riebckite gneiss-bearing part of Hesperian Massif: The Galineiro and surrounding areas. Vigo, Spain. - Leidse Geol. Med.,36, 1–203.Google Scholar
  17. — (1974): Alkaline gneisses. - The alkaline rocks ed. H. Sorensen, John Wiley & Sons, London.Google Scholar
  18. Gibson, I. L. (1970): A pantelleritic welded ash-flow tuff from the Ethiopian Rift Valey. - Contr. Min. Petr.,28, 89–111.Google Scholar
  19. — 1972): The geochemistry and petrogenesis of a suite of pantellerites from the Ethiopian Rift. - J. Petrol.,13, 21–44.Google Scholar
  20. ConÇalves, F. (1971): Subsidios para o conhecimento geologico do Nordeste Alentejano. - Mem. Serv. Geol. Portugal, n.18, 62 pp.Google Scholar
  21. Hess, P. C. (1977) Structure of silicate melts. - Can. Mineral.,15, 162–178.Google Scholar
  22. — &Wood, M. I. (1982): Aluminium coordenation in metaluminous and peralkaline silicate melts. - Cont. Min. Petr.,81, 102–112.Google Scholar
  23. Hlawatsch, C. (1906): über dem Amphibol von Cevadaes (Portugal). - Robenbusch-Festschrift, Stuttgart, 68–76 (Abst. in N. Jb. Min., 1908,1, 24–25).Google Scholar
  24. Ibarguchi, J. I. G. &Girone, E. O. (1981): Caracteristicas del metamorfismo en el sector septentrional de la unidad de Malpica-Tuy y terrenos adjacentes. (Galicia Occidental, España) - (Abs.). - VII Reunion de Geologia del Oeste Peninsular (Madrid).Google Scholar
  25. Iglesias, M.,Ribeiro, M. L. &Ribeiro, A. (1983): La interpretation aloctonista de la estrutura del noroeste peninsular. - Libro Jubilar J. M. Rios., Geologia de España, Tomo I, Inst. Geol. Min. España, pp. 459–467.Google Scholar
  26. Julivert, M.,Fontbote, J. M.,Ribeiro, A. &Conde, L. (1974): Memoria Explicativa del Mapa Tectonico de la Peninsula Iberica y Baleares. - Inst. Geol. Min. España, 113 p.Google Scholar
  27. Lacroix, A. (1916): Les syenites à riebckites d'Alter Pedroso (Portugal), leur forme mes ocrates (lusitanites) et leur transformation en leptinites et gneiss. - C. R. Ac. Sc. Paris,163, 279–282.Google Scholar
  28. — (1927): Les rhyolites et les trachytes hyperalkalin quartzifères a propos de ceux de la Corré e. - Compt. Rend. Acad. Sci. Paris,185, 1410–1415.Google Scholar
  29. Lotze, F. (1950): Observaciones respecto a la división de los variscides de la Meseta Ibérica. - Publ. extrangeras sobre geologia de España,V, 147–166.Google Scholar
  30. Macpherson, J. (1881): Apuntes petrográficos de Galicia. - An. Soc. Esp. Hist. Nat.,10, 49–87.Google Scholar
  31. Munha, J., Ribeiro, A. &Ribeiro, M. L. (1984): Blueschistes in the Iberian Variscan chain (Trás-os-Montes: NE Portugal). - Com. Serv. Geol. Portugal,70 (1), 31–53.Google Scholar
  32. Naslund, H. R. (1976): Liquid immiscibility in the system KAlSi3O8-NaAlSi3O8-FeO-Fe2O3-SiO2 and its application to natural magmas. - Carnagie Inst. Washington Yearb.,75, 592–597.Google Scholar
  33. Neiva, J. M. C. (1948): Rochas e minérios da regiÃo de BraganÇa-Vinhais. - Rel. Serv. Fom. Min.,14, 248 pp.Google Scholar
  34. Neves, J. M. C. (1959): Roches sodiques des regions d'Alter Pedroso et d'Elvas (Alentejo, Portugal). - 20th Int. Geol. Congress. Mexico City, 1856, seccion XI-A: Petrologia y Mineralogia, pp. 239–252.Google Scholar
  35. Noble, D. C. &Haffty, J. (1969): Minor element and revised major-element contents of some Mediterranean pantellerites and comendites. - J. Petrol.10, 3, 502–509.Google Scholar
  36. Osann, A. (1907): über einen Nephelinreichen Gneis von Cevadaes, Portugal. - N. Jb. Min., II, Abh., pp. 109–128.Google Scholar
  37. Paul, A. &Douglas, R. W. (1965a): Ferrous-ferric equilibrium in binary alkali silicate glasses. - Phys. Chem. Glasses,6, 207–211.Google Scholar
  38. Pondal, I. P. (1956): Nota explicativa del mapa geológico de la parte N.O. de la provincia de la Coruña.- Leidse Geol. Med.,21, 468–484.Google Scholar
  39. - (1967): Datos geológico-petrogràficos de la provincia de la Coruña. - Estudio agrobiológico de la provincia de la Coruña, Vigo, Artes gràficas de Faro de Vigo, 46 pp.Google Scholar
  40. Priem, H. N. A., Boelrijk, N. A. I. M., Verschure, R. H., Hebeda, E. H. &Verdurmen, E. A. TH. (1970): Dating events of acid plutonism through the Paleozoic of the Western Iberian Peninsula. - Ecl. Geol. Helv.63, 255–274.Google Scholar
  41. —, —,Hebeda, E. H., Verdurmen, E. A. TH. &Verschure, R. H. (1972): Upper Ordovician-lower Silurian acidic magmatism in the prehercynian basement of Western Galicia, NW Spain. - Progress Report, Lab. Isot. Geol. Amesterdam, pp. 123–127.Google Scholar
  42. Ribeiro, A. (1974): Contribution à l'étude tectonique de Trás-os-Montes Oriental. -Mem. Serv. Geol. Portugal, 24.Google Scholar
  43. —,Iglesias, M., Ribeiro, M. L. &Pereira, E. (1983): Modèle geodynamic des Hercynides Ibériques. - Com. Serv. Geol. Portugal,69 (2), 291–293.Google Scholar
  44. — &Ribeiro, M. L. (1972): Rochas hiperalcalinas da regiāo de Macedo de Cavaleiros (Trás-os-Montes Oriental). - Rev. Fac. Cienc. Lisboa,2. S-C-XVIII (1), pp. 301–321.Google Scholar
  45. Ribeiro, M. L.,Barnett, R. L.,Munhá, J.,Ribeiro, A. (1982): Blueschists in Eastern Trás-os-Montes (NE Portugal): evidence for overthrusting (Abs). - V. Semana de Geoquimica (Aveiro).Google Scholar
  46. — &Ribeiro, A. (1982): Nouvelles donnés sur le volcanism bimodal de l'unité Centro-transmontaine dans la région de Macedo de Cavaleiros (Trás-os-Montes Oriental). - Terra cognita,3, 202 (abstract).Google Scholar
  47. Schermerhorn, L. &Kotsch, S. (1984): First occurrence of lawsonite in Portugal and tectonic implications.- Com. Serv. Geol. Portugal.,70 (1), 23–29.Google Scholar
  48. Serralheiro, A. (1957): EsboÇo geológico da regiÃo de Alter Pedroso. - Bol. Sc. Geol. Portugal,12, fasc. III, 3–12.Google Scholar
  49. Shand, S. J. (1927): The eruptive rocks. - Wiley, New York.Google Scholar
  50. Shood, M. K. (1983): Modern Igenous Petrology. - A Wiley-interscience publication John Wiley & Sons. New York.Google Scholar
  51. Suess, E. (1897/1902): La face de la Terre (Das Antlitz der Erde). - Paris.Google Scholar
  52. Sun, S. S. &Nesbit, R. W. (1979): Geochemical characteristics of mid-ocean ridge basalts. - Earth Plan. Sc. Letters,44, 119–138.Google Scholar
  53. Teixeira, C. &AssunÇÃo, C. (1956): Notas sobre a geologia de Portugal; o complexo cristalofilino antigo. - Empr. Lit. Fluminense, Lisboa, 20 pp.Google Scholar
  54. — & —, (1958): Novos elementos para o conhecimento das rochas peralcalinas sódicas do Alto Alentejo. - Rev. Fac. Cienc. Univ. Lisboa, 2 série, C, 5, pp. 173–208.Google Scholar
  55. Thompson, R. N. &MacKenzie, W. S. (1967): Feldspar-liquid equilibria in peralkaline acid liquids: An experimental study. - Am. Journ. Sc., V, 265, 714–734.Google Scholar
  56. Webster, A. H. &Bright, N. F. H. (1961): The system iron-titanium-oxygen between 1 atm. and 1200 C and oxygen partial pressures between 1 atm. and 2×10 atm. - J. Am. Ceram. Soc.,44, 110–116.Google Scholar

Copyright information

© Ferdinand Enke Verlag Stuttgart 1987

Authors and Affiliations

  • M. Luisa Ribeiro
    • 1
  1. 1.ServiÇos Geológicos de PortugalR. Academia CiÊncias, 19LisboaPortugal

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