Geochemistry of lower Paleozoic anorogenic basic rocks from the Evora Massif (Western Ossa-Morena Zone, Portugal)
- Autores: M. Francisco Pereira, M. Chichorro, Patricia Moita, J. Francisco Santos, J.B. Silva
- Localización: Geogaceta, ISSN 0213-683X, Nº. 35, 2003, págs. 87-90
- Idioma: inglés
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Resumen
Undated basic rocks included in the Ossa-Morena westernrnost dornains (Alentejo region, PortugaD have been studied in an atternpt to fill the lack of geochernical data for the Evora Massif. The selected outcrops, interpreted to belong to the lower Paleozoic stratigraphic record, are mainly represented by amphibolites associated with metamorphosed detritic, carbonate and volcanic-sedimentary series. According to their petrography and variations of major, trace and REE elements, these basic rocks seem to derive from protoliths with tholeiitic basalt compositions probably related to an anorogenic geotectonic scenario controlled by transtension and the development of clastic and carbonate basin sedimentary sequences. Fractional crystallization of olivine, clinopyroxene and plagioclase may have played an important role in the generation of different melt composition, however, it is also necessary to invoke source heterogeneity and/or different degrees of partial melting of a mantle source with garnet Iherzolite composition to explain the observed range of incompatible trace element ratios. The most likely sources of the basaltic melts may have varied from depleted mantle (similar to N-MORB sources) to mantle rocks affected by within-plate enrichment.
