Holocene evolution of the Colima Volcanic Complex, Mexico

Current activity at the Colima Volcanic Complex (CVC) is characterised by the andesitic lava dome growth and small Vulcanian style eruptions of Volcán de Colima; however, road cuts on the nearby Nevado de Colima, reveal a record of explosive eruptions spanning the Holocene and Late Pleistocene. New data presented here, in combination with published and unpublished datasets, reveal the majority of tephra fallout deposits spanning the last ~13,000 years, are medium-K sub-alkaline, ranging in composition from basaltic-andesite to high-silica andesite (50.7 - 60.4 wt.% SiO2). These magmas display typical subduction-related trace element signatures with enriched fluid mobile elements (Rb, Ba, La, Ce, Sr) relative to high field strength elements (i.e. Nb, Ta). Three units interbedded in the CVC stratigraphy, erupted at c.7000, 12,000 and 13,000 years before present (yrs B.P.), reveal pulses of alkaline magmatism which intersect the magmatic storage region of the CVC on timescales of thousands of years. These units are mineralogically and geochemically distinct from the typical sub-alkaline eruption deposits, characterised by the presence of phlogopite and elevated K2O, P2O5 and incompatible trace element abundances. Through two-component mixing models, using whole-rock major and trace element geochemical data, and Sr-Nd isotopic data, after Langmuir et al. (1978), the alkaline component within these mixed magmas has been quantified to between 20 and 70%. A new model defining the nature of the magmatic plumbing system of the CVC is presented, drawing on previously published models for alkaline magma petrogenesis, recent geophysical studies, and new petrological and geochemical data. Mineral compositions and textures reveal multiple phases of growth and destabilisation interpreted to reflect decompression and magma recharge events consistent with multiple levels of magma storage within the crust below the CVC. Finally, initial volume estimates based on tephra modelling reveal these explosive eruptions were subplinian (0.03 to 0.3km3) events. These initial results reveal a link between magma composition and eruption volume, with the most evolved CVC magmas producing large volume eruptions.