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EPMA geochemical evidence of a long-lived Pleistocene Crystal-Mush in the Northern Andes: geothermobarometric challenges

César Bucheli1, Natalia Pardo1, · Patricia Larrea2, Cristina de Ignacio3

  • Affiliations: 1 Departamento de Geociencias, Universidad de Los Andes, Bogotá, D.C, Colombia 2 Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile 3 Departamento de Mineralogía y Petrología, Facultad de Ciencias Geológicas, Universidad Complutense, Madrid, Spain 

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 54

  • Programme No: 1.7.41

  • Theme 1 > Session 7

Abstract

We reconstruct the physicochemical conditions of melts in the Pleistocene storage and plumbing system of the Doña Juana Volcanic Complex in southwest Colombia. This complex is a little-known, potentially active polygenetic volcano with dacitic composition, consisting of four major edifices and experiencing long periods of dormancy. By analyzing compositional data from plagioclase, amphibole, pyroxene, and Fe-Ti oxides, along with new and existing whole-rock data from representative eruptive products, we conducted equilibrium tests and geothermobarometry calculations within a well-established stratigraphic, petrographic, and geochronological framework. The textural and geochemical variations in all mineral phases indicate a trans-crustal magmatic system that fueled the Pleistocene eruptions of Doña Juana, with cyclic rejuvenation of a crystal mush following each edifice collapse. The presence of different crystal cargos before magma recharge and eruption is evidenced by (i) the coexistence of equilibrium and disequilibrium textures and variable compositions in all studied crystal species, (ii) felsic cores in antecrysts, (iii) mafic overgrowth rims, and (iv) significantly less differentiated microcrysts compared to meso- and macrocrysts. By integrating multiple mineral-only and mineral-liquid geothermobarometers and conducting thorough textural analyses, we estimate the intensive parameters of the mush--melt interaction zone in the middle crust, offering a preliminary view of the architecture of a trans-crustal magmatic system in a complex tectonic setting within a previously understudied area of the north-Andean volcanic zone.