Alkaline Rocks and Carbonatites of the World

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Jaboticabal

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Occurrence number: 
025-00-069
Country: 
Brazil
Region: 
Sao Paulo
Location: 
Longitude: -48.47, Latitude: -21.17

The small intrusion of Jaboticabal is emplaced in Cretaceous basalts. To the west and northwest near Aparecida de Monte Alto, Taiuva and Piranji alkaline lavas up to 15 m thick intercalated in sandstones of the Bauru Group have been encountered in drill holes. The Jaboticabal rock is an analcime tinguaite consisting of euhedral nepheline, euhedral analcime, clear sanidine, which is less abundant than the former minerals, and aegirine-augite together with accessory magnetite, perovskite, sodic amphibole, aenigmatite, apatite, some interstitial natrolite and rare probable Zr-Ti silicates. The lavas are analcime-rich rocks (blairmorites) with no feldspar. Altered nepheline has been detected but analcime usually comprises the only salic mineral and constitutes more than half the rock. The pyroxene is titaniferous but there is some associated aegirine; perovskite, sphene and magnetite are plentiful and there is a little apatite and calcite. Chemical analyses of the tinguaite and a discussion of the relationship of this rock to the lavas will be found in Valarelli et al. (in press), and chemical analyses of the lavas in Coutinho et al. (1982).

Age: 
Gomes and Valarelli (1970) obtained an age of 54 Ma by K-Ar on analcime tinguaite and Coutinho et al. (1982) 61.6±2.5 Ma; the latter obtained 56.3±3.5 Ma for an analcimite lava.
References: 
J. M. V. Coutinho, personal communication, 1981. COUTINHO, J.M.V., COIMBRA, A.M., NETO, M.B. and ROCHA, G.A. 1982. Lavas alcalinas analcimiticas associadas ao Grupo Bauru (Kb) no Estado de Sao Paulo, Brasil. Quinto Congreso Latinamericano de Geologia, Argentina, Actas II: 185-96. GOMES, C.B. and VALARELLI, J.V. 1970. Nova ocorrencia de rochas alcalinas no estado de Sao Paulo. Resumo das comunicacoes, Congresso Brasileira de Geologia, 24: 336-7. VALARELLI, J.V., COUTINHO, J.M.V., FILHO, J.R.M. and GOMES, C.B. (in press). O tinguaite de Jaboticabal, SP. Boletim IGA, Instituto de Geociencias e Astronomia, Universidade de Sao Paulo
Fig. 203 Jaboticabal and location of drill holes which have penetrated alkaline lavas. The estimated minimum area underlain by the lavas is indicated (after Coutinho et al. 1982, p. 186).
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