Alkaline Rocks and Carbonatites of the World

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Sarmiento

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Occurrence number: 
008-00-014
Country: 
Argentina
Region: 
Chubut
Location: 
Longitude: -68.87, Latitude: -45.62

In the Sarmiento area occur numerous sills, ring dykes and radial dykes of alkaline basic rocks, principally teschenites, with differentiates of nepheline, analcime and zeolite syenites. They intrude tuffs of the Bajo Barreal Formation. Analcime basanite lavas are widespread in the area. The teschenites consist of plagioclase (An58-20), ophitic titanaugite, some larger crystals having thin aegirine-augite rims, olivine, interstitial analcime, a little zeolite, magnetite, apatite and rare biotite and nepheline. The syenitic differentiates, which are found only in some of the sills, occur as veins up to 40 m thick and may be pegmatitic. They comprise alkali feldspar, rare plagioclase, nepheline, interstitial analcime, sometimes zeolite, pyroxene zoned from augite to aegirine, rare arfvedsonite and olivine, opaques and apatite. Analyses are available in Pezzutti and Villar (1978).

Age: 
Tertiary.
References: 
PEZZUTTI, N. E. & VILLAR, L. M. 1978. Los complejos alcalinos en la zona de Sarmiento Provincia de Chubut. VII Congreso Geologico Argentino, Neuquen, 2‚ 511-20. TERUGGI, M. E. 1964. Differentiated zeolite- and nepheline-syenites in basic sills of central Patagonia. Report of 22nd Session, International Geological Congress, India, 7‚ 22-34.
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith