Alkaline Rocks and Carbonatites of the World

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Rio Reventazon

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Occurrence number: 
039-00-002
Country: 
Costa Rica
Region: 
Limon and Cartago
Location: 
Longitude: -83.05, Latitude: 10

In the area between the villages of Siquirres and Turrialba along the Rio Reventazon a number of teschenite sills outcrop which are associated with lavas of alkali basalt and basanite. The sills are up to 40 m thick and are emplaced in Tertiary marine sediments. Some sills are homogeneous and comprise olivine, salite, a brown amphibole, plagioclase (An55), analcime (30-35%) and a little biotite, apatite, zeolite, opaques and sometimes hauyne. Other sills pass from a mesocratic facies at lower levels, rich in olivine, clinopyroxene and labradorite with interstitial analcime and a little biotite, opaques, apatite and zeolite, to leucocratic rocks at higher levels containing only a little salite, andesine, much more abundant interstitial analcime, alkali feldspar, biotite, opaques, zeolites and apatite. There is some acicular aegirine-augite or aegirine and in some sills nepheline occurs.

Age: 
A specimen of basanite gave 4.6 ±0.25 Ma by K-Ar (Bellon and Tournon, 1978).
References: 
AZAMBE, B. and TOURNON, J. 1977. Les intrusions basiques alcalines du Rio Reventazon (Costa Rica). Compte Rendu Sommaire des Seances de la Societe Geologique de France, 2: 104-7. BELLON, H. and TOURNON, J. 1978. Contribution de la geochronometrie K-Ar a l'etude du magmatisme de Costa Rica, Amerique Centrale. Bulletin de la Societe Geologique de France, 20: 955-9. TOURNON, J. 1973. Presence de basaltes alcalins Recents au Costa Rica (Amerique Centrale). Bulletin Volcanologique, 36: 140-7
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith