The evolution of a monogenetic eruption: Navidad Eruption, Lonquimay Volcano, Chile
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Lonquimay Volcano, in the Central Southern Volcanic Zone (CSVZ) in Southern Chile, most recently erupted from December 25, 1988 to January 1990, dubbed the Navidad Eruption. The time span of this single continuous eruptions (thirteen months) provides insight into the potential for magmatic evolution over the course of a single eruption. For this research, three scoria samples, three lava samples, and one lava spatter sample were collected and processed. The whole rock chemistry of the Navidad Eruption did not evolve over time, however, the crystal content did undergo transitions. The further analysis of crystal compositions found evidence of basalt magma recharge interacting with a resident andesite magma to trigger this eruption. Direct evidence for this recharge was found in the mixing of separate source pyroxene crystals (Pigeonite and Augite) and olivine crystals that encapsulated melt inclusions. Geothermobarometry constrained the range of temperatures and pressures involved in the crystal growth and groundmass glass formations. Further evidence into this interaction was explored using Crystal Size Distribution (CSD), for basic plotted pattern recognition and the segmented linear regression that subsequently lead to resident time calculations for applicable crystal populations. The combination of ASTER and Landsat 7 data then corroborated the consistent whole rock composition while identifying areas of changing surface textures in the lava flows. These changing surfaces were categorized and seven major areas of recommended future research were identified. This research is particularly significant due to the identification of melt inclusions, located within several olivine crystals, and the clear identification of crystal populations (Pigeonite and Augite) unique to each of the two parent magmas despite extremely little variation in the overall eruption composition (<1% difference in major elements and <1ppm in most trace elements).