Abstract

MONSALVE, María Luisa et al. GEOLOGICAL CARACTERIZATION OF IZA VOLCANIC STRUCTURE, BOYACÁ - COLOMBIA ABSTRACT. bol.geol. [online]. 2011, vol.33, n.1, pp.117-130. ISSN 0120-0283.

Iza volcanic structure (5°36'20''N - 72°59'33'' W) is the result of rising riodacitic to ryolithic magmatic pulses, which didn´t reach the surface, the first of them giving origin to an intrusive breccias, interpreted as the result of indirect hot deep magma interaction with a sedimentary aquifer, leading to vapor overpressure and consequent fragmentation of the host rocks. The intrusive breccia form the Southern part of the Iza edifice, it is massive beige to light red in color, locally with pseudo columnar joint; it is composed by angular to subrounded sedimentary and minor igneous rock fragments in a porphyry rhyotlitic matrix. This stage is followed by dome emplacement which are dacitic to rhyolitic in composition. Petrographic analisys show that they are similar to the matrix breccia; they have a porphiritic texture, phenocrist of sanidine, quartz and plagioclase and glassy matrix. Locally the domes are fractured presenting breccias facies (autobreccia and Jig saw breccias, among others). Relationship with the host rock allow to interpreting the volcanic body as a crypto-domes, outcropping at surface by faulting and erosion.

Keywords : Iza; Intrusive Breccias; Dome; Cryptodome.

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