Resumo

TORO TORO, Luz Mary; BORRERO-PENA, Carlos Alberto  e  AYALA CARMONA, Luis Fernando. PETROGRAFÍA Y GEOQUÍMICA DE LAS ROCAS ANCESTRALES DEL VOLCÁN NEVADO DEL RUIZ. bol.geol. [online]. 2010, vol.32, n.1, pp.95-105. ISSN 0120-0283.

A model of the "Ruiz Ancestral" stage (2 to 1 Ma) at the Nevado del Ruiz Volcano is proposed. The extension of the lava remnants of this stage covered an area of about 200 Km² and they were cartographied around the Northeast-North-Northwest of the present edifice of the volcano. Whole-rock geochemical data of andesitic, basaltic-andesitic and dacitic samples from the different outcrops share the calcalkaline affinity with medium to high K contents. The trace elements range variation compared with SiO₂ suggests a fractional crystallization mechanism from the ferromagnesian minerals and the calcic plagioclase. The trace elements pattern is typical of a volcanic arc with Sr, K, Rb, Ba y Th enrichments and Nb impoverishment. The REE diagram shows a smooth slope and the typical LREE enrichment.

Palavras-chave : Ancestral Ruiz; Volcanic Arc; Andesites; Calcalkaline; Colombia.

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