Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: -49.1, Latitude: -24.95

Tunas comprises four coalescing intrusions covering 25 km2 which are cut by three intrusions of volcanic breccia. Several phonolite dykes up to 200 m thick extend to the northeast and southwest. The principal rock types are quartz syenite, nepheline syenite, foyaite and trachyte, with subordinate alkali gabbro and magmatic breccias. There is some metasomatism, especially of xenoliths.

K-Ar on biotite from syenite gave 11.5 Ma and on K-feldspar 73.8 Ma, while gabbro gave 108.4 Ma (Cordani and Hasui, 1968).
CORDANI, U.G. and HASUI, Y. 1968. Idades K-Ar de rochas alcalinas do primeiro planalto do estado do Parana. Anais Congresso Brasileiro de Geologia, 22: 149-53. FUCK, R.A. 1972. Geologia do macico alcalino de Tunas, Parana, Brazil. D.Sc. Thesis (unpublished), University of Sao Paulo, Institute of Geosciences. TREIN, E., MARINI, O.J. and FUCK, R.A. 1967. Rochas alcalinas no primeiro planalto do Estado do Parana. Boletim Paranaense de Geociencias, 23 e 25: 325-45. ULBRICH, H.H.G.J. and GOMES, C.B. 1981. Alkaline rocks from continental Brazil. Earth Science Reviews, 17: 135-54
Fig. 1_221 Tunas (from Ulbrich and Gomes, 1981, Fig. 6, which is after Fuck, 1972).
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