Istituto di Geoscienze e Georisorse     
Comin-Chiaramonti P., Civetta L., Petrini R., Piccirilo E., Bellieni G., Censi P., Bitschene P., Demarchi G., De Min A., De Barro Gomes C., Castillo A., Velazquez J. Tertiary nephelinitic magmatism in Eastern Paraguay: Petrology, Sr-Nd isotopes and genetic relationships with associated spinel-peridotite xenoliths. In: European Journal of Mineralogy, vol. 3 (3) pp. 507 - 525. Schweizerbart, 1991.
Plugs, flows and dykes of nephelinitic (and ankaramitic) rocks occur near Asunción (Eastern Paraguay; 61-39 Ma). This magmatism occurs at the western boundary of the Paraná basin and is associated with NW-SE-trending rift and antiform structures. Nephelinites contain variable amounts of crustal (sedimentary, metamorphic and volcanic) and mantle (spinel-peridotite) xenoliths. The genesis of the Asunción nephelinites requires a mantle source geochemically and isotopically distinct from that represented by the spinel-peridotite nodules included in the lavas. The most likely mantle source is a gamet peridotite characterized by small-scale heterogeneities, at least in terms of Sr and Nd isotopes. This mantle source was subjected to (1) low degrees of partial melting (e.g. 3 - 4%), (2) enrichment in Nb, Ba, La, Ce, Sr and P relative to a primordial mantle. It is suggested that the enrichment in incompatible elements may be due to metasomatic processes related to a thermal anomaly responsible for the generation of the Lower Cretaceous Paraná flood lavas. The initial Sr isotope ratios of the Asunción nephelinites (R₀ = 0.7036-0.7039) indicate a mantle source distinct from that of the Lower Cretaceous magmatism (Central-Eastern Paraguay: alkaline magmatism, R₀ = 0.7073 ; tholeiitic flood basalts, R₀ = 0.7059).
URL: http://www.schweizerbart.de/j/ejm/
Subject Eastern Paraguay
South America
Tertiary nephelinites
Mantle source
Sr-Nd isotopes
partail melting

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