stripes
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).
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 Potassium-argon ages of some alkaline rocks from southern Brazil.Thesis (unpublished), University of California, Berkeley. 145 pp.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