Hostname: page-component-76fb5796d-qxdb6 Total loading time: 0 Render date: 2024-04-25T08:54:34.413Z Has data issue: false hasContentIssue false
  • English
  • Français

Podiform chromitite-bearing ultrabasic rocks from the Bragança Massif, northern Portugal: fragments of island arc mantle?

Published online by Cambridge University Press:  01 May 2009

J. C. Bridges ,
H. M. Prichard  and
C. A. Meireles
J. C. Bridges
Affiliation:
Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, UK
H. M. Prichard
Affiliation:
Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, UK
C. A. Meireles
Affiliation:
Servicos Geológicos de Portugal, Rua da Amieira, 4466 S. Mamede de Infesta, Portugal
Get access Rights & Permissions [Opens in a new window]

Abstract

The Upper Allochthonous Thrust Complex (UATC) of the Bragança massif in northern Portugal contains a set of ultrabasic rocks interthrust with granulites. The ultrabasic rocks have refractory silicate mineral and whole rock compositions which indicate an origin as depleted mantle. Phase relationships of harzburgite samples suggest that they formed in equilibrium with high-Mg picritic melts created through a high degree of mantle partial melt extraction. Chromite in small podiform deposits has 100 Cr/(Cr + Al) ratios of 62–85, which are consistent with crystallization from such melts. Most of the chromite composition parameters are similar to those of ophiolite deposits except for the high ferric iron contents (2.77–8.95 wt% Fe2O3). Such enrichment is a feature of chromite from island arc magmas. It is suggested that the extensive partial melt extraction and chromite mineralization in the ultrabasic rocks occurred in the upper few kilometres of island arc mantle. The ultrabasic rocks were tectonically emplaced into a granulite and eclogite-bearing arc-continent collision complex during the Early Ordovician and subsequently, in the mid-Devonian emplaced over the Central-Iberian terrane.

Type
Articles
Information
Geological Magazine , Volume 132 , Issue 1 , January 1995 , pp. 39 - 49
Copyright
Copyright © Cambridge University Press 1995

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Augé, T., & Roberts, S., 1982. Petrology and geochemistry of some chromitiferous bodies within the Oman ophiolite. Ofioliti 3, 133–54.Google Scholar
Bacuta, G. C. Jr, Kay, R. W., Gibbs, A. K., & Lipin, B. R., 1990. Platinum-group element abundances and distribution in chromite deposits of the Acoje Block, Zambales ophiolite complex, Philippines. Journal of Geochemical Exploration 37, 113–45.CrossRefGoogle Scholar
Ballhaus, C. G., Berry, R. F., & Green, D. H., 1991. High pressure experimental calibration of the olivineorthopyroxene-spinel oxygen barometer: implications for the oxidation state of the upper mantle. Contributions to Mineralogy and Petrology 107, 27–40.CrossRefGoogle Scholar
Bernard-Griffiths, J., Peucat, J.-J., Cornichet, J., Iglesias Ponce De Leon, M., & Gil, J. I. Ibarguchi, 1985. U-Pb, Nd isotope and REE geochemistry in eclogites from the Cabo Ortegal Complex, Galicia, Spain: an example of REE immobility conserving MORB-like patterns during high-grade metamorphism. Chemical Geology 52, 217–25.Google Scholar
Boyd, F. R., 1989. Compositional distinction between oceanic and cratonic lithosphere. Earth and Planetary Science Letters 96, 15–26.CrossRefGoogle Scholar
Bridges, J. C., Prichard, H. M., Neary, C. R., & Meireles, C., 1993. Platinum-group element mineralization in chromite-rich rocks of the Bragança massif, N. Portugal. Transactions of the Institution of Mining and Metallurgy (Section B: Applied Earth Science) 102, B55–134.Google Scholar
Burgath, K., & Weiser, T., 1980. Primary features and genesis of Greek podiform chromite deposits. In Ophiolites: Proceedings of the International Ophiolite Symposium. Cyprus, 1979 (ed. Panayiotou, A.), pp. 675–90. Geological Survey Department, Ministry of Agriculture and Natural Resources, Republic of Cyprus.Google Scholar
Burkhard, D. J. M., 1993. Accessory chromium spinels: their coexistence and alteration in serpentinites. Geochimica et Cosmochimica Acta 57, 1297–1306.CrossRefGoogle Scholar
Christiansen, F. G., 1986. Structural classification of ophiolitic chromite deposits. In Metallogeny of Basic and Ultrabasic Rocks (eds Gallagher, M. J., Ixer, R. A., Neary, C. R. and Prichard, H. M.), pp. 279–89. London: The Institution of Mining and Metallurgy.Google Scholar
Crawford, A. J., Falloon, T. J., & Green, D. H., 1989. Classification, petrogenesis and tectonic setting of boninites. In Boninites (ed. Crawford, A. J.), pp. 1–44. London: Unwin Hyman.Google Scholar
Dallmeyer, R. D., & Tucker, R. D., 1993. U-Pb zircon age for the Lagoa augen gneiss, Morais complex, Portugal: tectonic implications. Journal of the Geological Society 150, 405–10.CrossRefGoogle Scholar
Dick, H. J. B., & Bullen, T., 1984. Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas. Contributions to Mineralogy and Petrology 86, 54–76.CrossRefGoogle Scholar
Drury, S. A., 1980. The geochemistry of high pressure gneisses from Cabo Ortegal (NW Spain): residues of deep anatexis. Geologie en Mijnbouw 59, 61–4.Google Scholar
Economou, G., & Economou, M. I., 1986. Some chromite occurrences from the areas of Vermio and Veria, Macedonia, Greece. In Metallogeny of Basic and Ultrabasic Rocks (eds Gallagher, M. J., Ixer, R. A., Neary, C. R. and Prichard, H. M. ), pp. 351–4. London: The Institution of Mining and Metallurgy.Google Scholar
Eggins, S. M., 1993. Origin and differentiation of picritic arc magmas, Ambae (Aoba), Vanuatu. Contributions to Mineralogy and Petrology 114, 79–100.CrossRefGoogle Scholar
Evans, C., & Hawkins, J. W., 1989. Compositional heterogeneities in upper mantle peridotites from the Zambales Range ophiolite, Luzon, Philippines. Tectonophysics 168, 23–41.CrossRefGoogle Scholar
Gass, I. G., Neary, C. R., Prichard, H. M., &Bartholomew, I. D., 1982. The chromite of the Shetland ophiolite: a re-appraisal in the light of new theory and techniques. Unpublished report for the commission of European Communities, Milton Keynes: The Open University, 264 pp.Google Scholar
Green, D. H., 1976. Experimental testing of ‘equilibrium’ partial melting of peridotite under water-saturated, high pressure conditions.. Canadian Mineralogist 14, 255–68.Google Scholar
Greenbaum, D., 1977. The chromitiferous rocks of the Troodos ophiolite complex, Cyprus. Economic Geology 72, 1175–94.CrossRefGoogle Scholar
Jan, Q. M., Windley, B. F., & Khan, A., 1985. The Waziristan Ophiolite Pakistan: general geology and chemistry of chromite and associated phases. Economic Geology 80, 294–306.CrossRefGoogle Scholar
Kepezhinskas, P. K., Taylor, R. N., & Tanaka, H., 1993. Geochemistry of plutonic spinels from the North Kamchatka Arc: comparisons with spinels from other tectonic settings. Mineralogical Magazine 389, 575–89.CrossRefGoogle Scholar
Kienle, J., Swanson, S. E., & Pulpan, H., 1983. Magmatism and subduction in the eastern Aleutian Arc. In Arc Volcanism: Physics and Tectonics (eds Shimozuru, D. and Yokoyama, I.), pp. 191–224. Tokyo: Terrapub.Google Scholar
Neary, C. R., & Brown, M. A., 1979. Chromites from Al ‘Ays complex, Saudi Arabia and the Semail complex, Oman. In Evolution and Mineralisation of the Arabian-Nubian Shield (ed. Al, A. M. S. Shanti), pp. 193–205. IAG Bulletin no. 2.CrossRefGoogle Scholar
Nicolas, A., 1989. Structures of Ophiolites and Dynamics of Oceanic Lithosphere. Dordrecht: Kluwer, 367 pp.CrossRefGoogle Scholar
O’Hara, M. J., 1968. The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks. Earth-Science Reviews 4 69–133.CrossRefGoogle Scholar
Pearce, J. A., Alabaster, T., Shelton, A. W., & Searle, M. P., 1981. The Oman ophiolite as a Cretaceous arc-basin complex: evidence and implications. Philosophical Transactions of the Royal Society of London A 300, 217–442.Google Scholar
Pearce, J. A., Lippard, S. J., & Roberts, S., 1984. Characteristics and tectonic significance of supra subduction zone ophiolites. In Marginal Basin Geology (eds Kokelaar, B. P. and Howells, M. F.), pp. 77–94. Geological Society of London Special Publication no. 16.Google Scholar
Peck, D. C., & Keays, R. R., 1990. Geology, geochemistry, and origin of platinum-group element-chromitite occurrences in the Heazlewood River Complex, Tasmania. Economic Geology 85, 765–93.CrossRefGoogle Scholar
Peucat, J. J., Bernard-Griffiths, J., Gil, J. I. Ibarguchi, Dallmeyer, R. D., Menot, R. P., Cornichet, J., & Iglesias Ponce De Leon, M., 1990. Geochemical and geochronological cross section of the deep variscan crust: the Cabo Ortegal high-pressure nappe (northwestern Spain). Tectonophysics 177, 263–92.CrossRefGoogle Scholar
Potts, P. J., 1984. Energy dispersive X-ray fluorescence analysis of silicate rocks for major and trace elements. X-ray Spectrometry 13, 2–15.CrossRefGoogle Scholar
Ribeiro, A., 1974. Contribution à ľétude tectonique de Trásos-montes oriental. Serviços Geológicos de Portugal 24 (Nova Série), 168 pp.Google Scholar
Ribeiro, A., Pereira, E., & Dias, R., 1990. Structure of Centro-Iberian Allochthon in the northwest of the Iberian peninsula. In Pre-Mesozoic Geology of Iberia (eds Dallmeyer, R. D. and Garcia, E. Martinez), pp. 220–36. Berlin, Heidelberg: Springer-Verlag.CrossRefGoogle Scholar
Ribeiro, A., Queseda, C., & Dallmeyer, R. D., 1990. Geodynamic evolution of the Iberian Massif. In Pre-Mesozoic Geology of Iberia (eds Dallmeyery, R. D. and Martinez Garcia, E.), pp. 399–409. Berlin, Heidelberg: Springer-Verlag.CrossRefGoogle Scholar
Ries, A. C., & Shackleton, R. M., 1971. Catazonal complexes of N.W. Spain and N. Portugal, remnants of a Hercynian thrust plate. Nature 234, 65–8.Google Scholar
Roberts, S., 1992. Influence of the partial melting regime on the formation of ophiolitic chromitite. In Ophiolites and their Modern Oceanic Analogues (eds Parson, L. M., Murton, B. J. and Browning, P.), pp. 203–17. Geological Society of London Special Publication no. 60.Google Scholar
Robertson, A. H. F., & Woodcock, N. H., 1980. In Ophiolites: Proceedings of the International Ophiolite Symposium. Cyprus, 1979 (ed. Panayiotou, A.), pp. 36–49. Geological Survey Department, Ministry of Agriculture and Natural Resources, Republic of Cyprus.Google Scholar
Sack, R. O., & Ghiorso, M. S., 1991. Chromian spinels as petrogenic indicators: thermodynamics and petrological applications. American Mineralogist 76, 827–47.Google Scholar
Wood, B. J., & Virgo, D., 1989. Upper mantle oxidation state: ferric iron contents of lherzolite spinels by 57Fe Mössbauer spectroscopy and resultant oxygen fugacities. Geochimica et Cosmochimica Acta 53, 1277–91.CrossRefGoogle Scholar