Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Rio Reventazon


Occurrence number: 
Costa Rica
Limon and Cartago
Longitude: -83.58, 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.

A specimen of basanite gave 4.6 ±0.25 Ma by K-Ar (Bellon and Tournon, 1978).

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