Alkaline Rocks and Carbonatites of the World

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Chajan

stripes

Occurrence number: 
008-00-009
Country: 
Argentina
Region: 
Cordoba and San Luis
Location: 
Longitude: -65, Latitude: -33.25

Nepheline basalts form the plugs of La Leoncita, La Madera, La Piedra and La Garrapata, all having diameters of about 1 km, while the plug of Cerro Piedra is much smaller. They cut Precambrian micaceous gneisses and form prominent hills. The rock of the plugs comprises olivine, pyroxene, nepheline, perovskite and magnetite and in some varieties biotite and analcime. Cortellezi et al. (1981) report 16% modal leucite in a rock from a quarry in La Garrapata, the pyroxene of this rock being aegirine-augite.

Age: 
Ages of 75±5 Ma on rocks from La Garrapata and 66±5 Ma from La Leoncita, both by K-Ar, have been obtained (Valencio et al. , 1980).
References: 
CORTELLEZZI, C. R. , TRAVERSA, L. & PAVLICEVIC, R. R. 1981. Estudio petrologica y ensayos fisicos de las rocas alcalinas del sur las provincias de Cordoba y San Luis. VIII Congreso Geologica Argentina, 4‚ 885-901. LOPEZ, M. G. 1979. Sobre las manifestaciones volcanicas alcalinas de la region de Villa Mercedes-Chajan, Provincias de San Luis y Cordoba. Trabajo Final de Licenciatara, Depto. Ciencias Geol. , Univ. Buenos Aires. PANDOLFI, C. I. de 1943. Estudio petrografico y bosquejo geologico de la Region de Chajan (Cordoba). Boletin, Ministerio de Agricultura de la Nacion. Direccion de Minas y Geologia, 54‚ 1-46. VALENCIO, D. A., LOPEZ, M. G., SOLA, P. & VILLANI, C. 1980. El significado geologico de los resultados del estadio paleomagnetico de vulcanitas alcalinas de los provincias de San Luis y Cordoba. Revista, Asociacion Geologica Argentina, 35‚ 340-7.
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