Alkaline Rocks and Carbonatites of the World

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Cananeia

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Occurrence number: 
025-00-110
Country: 
Brazil
Region: 
Sao Paulo
Location: 
Longitude: -47.9, Latitude: -24.97

A stock of less than 1 km2 forms the hill of Sao Joao and is surrounded by Recent sediments which obscure the contacts. The principal rocks are biotite pulaskite and nordmarkite, the latter containing quartz; both rock types include amphibole and a diopsidic pyroxene. The stock is cut by riebeckite solvsbergite dykes, and may be related to nordmarkite outcrops on nearby Ilha Comprida (Ulbrich and Gomes, 1981).

Age: 
K-Ar on alkali feldspar, barkevikite and biotite from nordmarkite gave 80.7-84.4 Ma (Amaral et al. 1967). Bushee (1974) obtained, also by K-Ar, 84.4 Ma on alkali feldspar, 82.3 Ma on barkevikite and 80.7 Ma on biotite, all from nordmarkite.
References: 
AMARAL, G., BUSHEE, J., CORDANI, U.G., KAWASHITA, K. and REYNOLDS, J.H. 1967. Potassium-argon ages of alkaline rocks from southern Brazil. Geochimica et Cosmochimica Acta, 31: 117-42. BUSHEE, J.M. 1974. Potassium-argon ages of some alkaline rocks from southern Brazil.Thesis (unpublished), University of California, Berkeley. 145 pp. FREITAS, R.O. de, 1947b Eruptivas alcalinas de Cananeia. Boletim da Faculdade de Filosofia, Ciencias e Letras, Universidade de Sao Paulo, Geologia, 4: 1-35. ULBRICH, H.H.G.J. and GOMES, C.B. 1981. Alkaline rocks from continental Brazil. Earth Science Reviews, 17: 135-54
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