Alkaline Rocks and Carbonatites of the World

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Cerro Nopal And Cerro Murcielago


Occurrence number: 
Longitude: -98.07, Latitude: 22.08

Lying 80 km southwest of the Sierra de Tamaulipas are two alkaline intrusions which are probably laccolithic in form, together with accompanying dykes. The rocks are phonolites of oligoclase, aegirine, nepheline and glass and tinguaites of alkali feldspar, nepheline, analcime, aegirine, sodic amphibole, biotite and opaques. Xenoliths of pyroxene-bearing peridotite occur in Cerro Nopal.

K-Ar on nepheline syenite gave 23.5+-0.7 Ma (Cantagrel and Robin, 1979, Table 1).
CANTAGREL, J-M. and ROBIN, C. 1979. K-Ar dating on eastern Mexican volcanic rocks - relations between the andesitic and the alkaline provinces. Journal of Volcanology and Geothermal Research, 5: 99-114. ROBIN, C. 1976. El vulcanismo de las plancies de la Huasteca (Este de Mexico). Datos geoquimicos y petrograficos. Boletin Universidad Nacional Autonoma de Mexico. Instituto de Geologia, 96: 55-92. ROBIN, C. 1982. Relations volcanologie - magmatologie - geodynamique: application au passage entre volcanismes alcalin et andesitique dans le sud Mexicain. Annales Scientifiques de l'Universite de Clermont-Ferrand II: Geologie Mineralogie, 70: 1-503
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