MAGMATIC PROCESSES IN THE NEVADO DEL RUIZ VOLCANO: AQUANTITATIVE TEXTURAL ANALYSIS
Published 2011-12-06
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Abstract
A detailed petrographic analysis of lava flows of the Nevado del Ruiz Volcano (VNR), including determination of mineral assemblages and microstructures, geochemical analysis and a crystal size distribution (CSD) quantitative textural analysis in plagioclases, helps to constrain interpretations of magmatic processes occurringin this volcano during the last 1,8 Ma. The VNR is one of the northern most active strato volcanoes in the Colombian Central Cordillera and displays a typical behavior of a subduction zone volcano with calc-alkaline affinity. This volcano had an eruptive period dominated by effusive behavior during the Pleistocene and itsproducts show a monotonous bulk composition, mainly andesitic to dacitic. Samples analyzed in this work are two-pyroxene andesites ± oxyhornblende ± biotite, with porphyritic and glomeroporphyritic microstructures. Plagioclase displays overgrow and resorption microstructures and crystaloscillatory zoning patterns. There are two plagioclase populations: one with crystals showing finely sievedinteriors and clean rims, the other is a population of clean plagioclase crystals lacking any sieved microstructures.The CSD curves show patterns of curvilinear and concave distributions, similar for all samples, with theexception of the lava domes, that show a linear pattern. Pyroxene has poikilitic and resorption microstructures(coarse cellular microstructures) and amphibole shows reaction rims. These characteristics allow to infer abruptchanges in melt composition during the crystallization process probably related with magma mixing processes.
Keywords: Crystal Size Distribution, Colombian Central Cordillera, Nevado del Ruiz Volcano, Igneous Petrology
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References
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