MAGMATIC PROCESS IN THE NEVADO DEL RUIZ VOLCANO, COLOMBIA: A QUANTITATIVE TEXTURAL ANALYSIS

A detailed petrographic analysis of lavas from flows of the Nevado del Ruiz Volcano, including determination of mineral assemblages, reaction textures and a quantitative textural analysis by crystal size distribution (CSD), helps to understand magmatic processes occurring in a magma chamber of an active Volcano of the Colombian Central Cordillera in the last 1,2 Ma.

The Nevado del Ruiz Volcano, an active stratovolcano in the Colombian Central Cordillera, 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. Reported whole rock K/Ar ages of andesitic-basaltic lava flows show a range between 1.2 ± 0.08 Ma for older lavas to 0 ± 0.05 Ma for recent lavas.

Lava flows consist of two-pyroxene andesites - basalts ± oxyhornblende, augite-oxyhornblende andesites, augite andesites and biotite-amphibole andesites. These rocks usually have porphyritic and glomeroporphyritic textures. Plagioclase displays overgrow textures, crystal oscillatory zoning patterns, corona textures, sieve and embayment textures, pyroxene has poikilitic textures and amphibole shows reaction rims. These characteristics allow to infer abrupt changes in melt composition during the crystallization process.