Alkaline Rocks and Carbonatites of the World

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Los Antiguos

stripes

Occurrence number: 
008-00-016
Country: 
Argentina
Region: 
Santa Cruz
Location: 
Longitude: -71.67, Latitude: -46.58

Two intrusions of teschenite with syenitic differentiates occur to the south of Lago Buenos Aires, one 11 km southeast of Los Antiguos, the other in the Rio Jeinemeni on the border with Chile, 30 km south-southwest of Los Antiguos (Busteros & Lapido, 1983, Fig. 1_1). The teschenites consist of intermediate plagioclase, orthoclase, a little nepheline, often replaced by analcime, 20-25% analcime, abundant olivine, augite/aegirine-augite, biotite and accessories. Syenites are composed of alkali feldspar, sometimes perthitic, albite-oligoclase, about 5% nepheline, which may be replaced by analcime, zeolites, aegirine-augite/aegirine, arfvedsonite and biotite. Rock analyses are available.

Age: 
Teschenite gave 46±3 Ma by K-Ar.
References: 
BUSTEROS, A. G. & LAPIDO, O. R. 1983. Rocas basicas en la vertiente noroccidental de la meseta del Lago Buenos Aires, Provincia de Santa Cruz. Revista Asociacion Geologica Argentina, 38‚ 427-36.
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