Andesitic (SiO2: similar to 60 wt%) monogenetic volcanism in the northern Colombian Andes: Crystallisation history of three Quaternary volcanoes

Abstract

The Quaternary Villamaria-Termales Monogenetic Volcanic Field (VTMVF) is one of the monogenetic fields located within the subduction related. volcanic chain in the northern Colombian Andes. The dominantly andesitic composition of the products from this field provides an opportunity to study the crystallisation history of monogenetic volcanic products, associated with long term crustal stagnation before eruption. This work focuses on the Victoria, Gallinazo and Tesorito monogenetic effusive volcanoes, using a combination of petrography, mineral chemistry and whole-rock chemical analysis, in addition to geothermobarometers, to estimate the crystallisation conditions of the main mineral phases and infer the depths at which such phases crystallised. We also present two K/Ar radiometric ages for Victoria and Gallinazo volcanoes in order to add to the known age (1.2 Ma) of the Tesorito volcano. This helps us to timeframe this volcanism within the similar to 140 km volcanic chain where it is located. The rocks are porphyritic with a glassy and microcrystalline groundmass, and display glomeroporphyritic and disequilibrium textures such as textures sieve in plagioclase and reaction rims in pyroxene.The main mineral phases forming the rocks arc plagioclase (An(22-)(67)), orthopyroxene (Wo(02)En(65)(-)(80)FS(18-)(33)), clinopyroxene (Wo(39-45)En(39-49)Fs(07-17)), amphibole (magnesiohastingsite, magnesihornblende, edenite and tschermakite), and Fe-Ti oxides Usp(37-23) Mag(63-77) and Ilm(79-62) Hem(21-39). Olivine (Fo(71-87)) only appears in the Victoria volcano. The volcanoes are subalkaline andesites with talc-alkaline affinity. Estimation of the crystallisation conditions (i.e. temperature and pressure) for in-equilibrium mineral phases, indicate the depths at which they crystallised. Olivine crystallised at 1198-1191 degrees C and similar to 1.4 GPa, orthopyroxene-clinopyroxene coexisted at 963-880 degrees C and 0.78-0.47 GPa, plagioclase formed at 928-908 degrees C and 0.76-0.17 GPa, amphibole crystallised at 998-877 degrees C and 0.79-0.16 GPa, and Fe-Ti oxides crystallised at 937-904 degrees C. This suggests that crystallisation starts at depths of similar to 53 km and it continues until the surface. The obtained radiometric ages for the Gallinazo (1.92 +/- 0.06 Ma) and Victoria (1.97 4-0.06 Ma) volcanoes indicate that they are similar to 0.7 Ma older than the nearby Tesorito volcano. (C) 2021 Elsevier B.V. All rights reserved.