UNDERSTANDING MAGMATIC PROCESSES AT TELICA VOLCANO, NICARAGUA: CRYSTAL SIZE DISTRIBUTION AND TEXTURAL ANALYSIS

Crystal size distribution (CSD) profiles of plagioclase feldspar phenocrysts were determined from basalts and basaltic-andesites of Telica volcano, Nicaragua to investigate magmatic processes. Telica volcano currently exhibits persistent activity with continuous seismicity and degassing, yet has not produced lava flows since 1529. Textural analysis of fourteen highly crystalline rock samples (>50 vol.% phenocrysts) from historic and pre-historic lava flows discovered that the samples are dominated by sieve-textured plagioclase feldspar phenocrysts. The sieve textures indicate thermochemical disequilibrium within the magmatic system. The CSD curves display an inverse relationship between population density and phenocryst length. Concave-up patterns observed for the Telica lava samples can be separated into two linear segments that define the two crystal populations; a steeply-sloping segment for the small crystals and a gently-sloping segment for large crystals. The two crystal populations may be explained by magma replenishment and mixing models in which a more mafic magma is introduced to the preexisting evolving chamber. Residence times calculated using the defined linear segments of the CSD curves suggest magmatic processes that occur on the order of decades to centuries. Despite the absence of lava flows in recent activity, the crystal size distributions and textural analysis advocate for the current persistent activity as being constant throughout the history of Telica.