Alkaline Rocks and Carbonatites of the World

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Morro Redondo

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Occurrence number: 
025-00-087
Country: 
Brazil
Region: 
Rio de Janeiro
Location: 
Longitude: -44.33, Latitude: -22.48

This is an approximately circular intrusion of about 5 km2 cutting Precambrian gneisses, but overlapped on the northern side by Tertiary sedimentary rocks. Biotite foyaite is the most abundant rock type of the intrusion, but sodalite syenites of albite, anorthoclase, aegirine and sodalite also occur. Leucite trachyte with phenocrysts of anorthoclase, amphibole, pyroxene and small leucites has been described.

Age: 
65 Ma (Ribeiro and Cordani, 1966 quoted in Asmus, 1978).
References: 
ASMUS, H.E. 1978. Hipoteses sobre a origem dos sistemas de zonas de fratura oceanicas alinhamentos continentais que ocorrem nas regioes sudeste e sul do Brasil. In. Petrobras. Aspectos estruturais da margem continental leste e sudeste do Brasil. CENPES/DINTEP, Rio de Janeiro (Serie Projeto Remac, no. 4): 39-73. BARBOSA, O. 1933. Eruptivas de Lages, Santa Catarina. Boletim Servico Geologico e Mineralogico, Rio de Janeiro, 69: 15-8. Lamego, 1936.
Fig. 204 Distribution of alkaline rocks around Rio de Janeiro.
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith