Abstract

RODRIGUEZ G., Gabriel  and  ZAPATA G., Gilberto. CHARACTERISTICS OF PLUTONISM UPPER MIOCENE IN THE NORTH SEGMENT OF CORDILLERA OCCIDENTAL AND ITS TECTONICS IMPLICATIONS IN THE NORTH-WEST COLOMBIAN GEOLOGICAL MODEL. Bol. cienc. tierra [online]. 2012, n.31, pp.5-22. ISSN 0120-3630.

In the north segment of Colombia's Cordillera Occidental, at the north of Itsmina's folded belt and the fault of San Juan's river located between Tatamá Hill and Farallones del Citara, outcrop a group of plutons that intrude Santa Cecilia - La Equis - Batolito de Mandé Complex (Chocó - Panamá arc), Cañasgordas Complex and El Botón's Basalts (El Botón's arc). They are intrusive bodies outcropping from Pueblo Rico (Risaralda) until Dabeiba (Antioquia). Plutons's composition belong to a group of gabro-monzodiorite-monzonite-sienite, with facies in some bodies of the group conformed by cuarzodiorite, cuarzomonzodiorite. In addition, only Farallones's Monzodiorite has signs classified as tonalites and granodiorites The chemical composition of the intrusive bodies is similar to El Botón's Basalts. These belong to the shoshonitic group with a high concentration of alkali rocks (Na₂O + K₂O > 5 wt%), high proportions K₂O/ Na₂O (> 0,6 a los 50% wt de SiO₂, >1,0 a los 55% wt de SiO₂), low TiO₂ (<1,3 % wt), high but changeable Al2O3 (14-19 %wt). Only few bodies such as San Juan's river diorite and small bodies of gabbro placed in Santa Cecilia-La Equis Complex have affinity with calco-alkaline's group. Rare earths and its trace elements behavior is due to rocks created by an arc formed by subduction. Plutons's ages Ar-Ar and K-Ar, show values between 9 and 12 million years (Tortonian- Serravallian age). They are similar to El Botón's Basalts and Combia formation. The formation of volcanic arc El Botón and all its associated plutons was originated in the margin of the blocks conformed by Santa Cecilia- La Equis- Batolito de Mandé complex and Cañasgordas Complex; suggesting that the Chocó-Panama Arc was already bonded from the Miocene.

Keywords : Cordillera Occidental plutons; shoshonite; Petrography; Geochemistry; Geochronology.

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