CARACTERIZACIÓN GEOLÓGICA DEL CUERPO VOLCÁNICO DE IZA, BOYACÁ - COLOMBIA
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Universidad Industrial de Santander
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El cuerpo volcánico de Iza (5°36’20’’N – 72°59’33’’ W) corresponde a pulsos de ascenso de magmariodacítico a riolítico, que no alcanzaron la superficie, el primero de ellos dio origen a una brecha intrusiva, resultado del movimiento del magma en profundidad, que al entrar en contacto con un posible acuífero en rocas sedimentarias, induce a la sobre saturación en volátiles y a su disrupción. La brecha, que forma el sector sur del cuerpo volcánico, es masiva, color habano a rojizo, con disyunción seudocolumnar, compuesta por fragmentos angulares-subredondeados de rocas sedimentarias y en menor cantidad ígneas, embebidos en una matriz de roca ígnea porfirítica. Esta fase es seguida por emplazamiento de domos (criptodomos), correspondientes a rocas de composición riodacítica– riolítica, petrográficamente similares a la matriz de la brecha, presentan textura porfirítica, confenocristales de sanidina, cuarzo y plagioclasa y matriz afanítica vítrea. Localmente, y en menor escala, el domo se encuentra fracturado y presenta facies brechosas (autobrechas y rompecabezas entre otros). Por relaciones con la secuencia sedimentaria encajante, se plantea que este cuerpo fue emplazado como criptodomos, expuestos en superficie por fallamiento y erosión.
Palabras clave: Iza, Brecha intrusiva, Domos, Criptodomos.
Iza volcanic structure (5°36’20’’N – 72°59’33’’ W) is the result of rising riodacitic to ryolithicmagmatic 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 brecciaform the Southern part of the Iza edifice, it is massive beige to light red in color, locally with pseudocolumnar 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 a redacitic 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 glassymatrix. 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 cryptodomes,outcropping at surface by faulting and erosion. Keywords: Iza, Intrusive Breccias, Dome, Cryptodome.
Iza volcanic structure (5°36’20’’N – 72°59’33’’ W) is the result of rising riodacitic to ryolithicmagmatic 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 brecciaform the Southern part of the Iza edifice, it is massive beige to light red in color, locally with pseudocolumnar 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 a redacitic 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 glassymatrix. 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 cryptodomes,outcropping at surface by faulting and erosion. Keywords: Iza, Intrusive Breccias, Dome, Cryptodome.