Volcán de Colima, in Western Mexico, is one of North America’s most active volcanoes.  Field studies, and petrological and geochemical analyses on explosive eruption deposits exposed in road cuts on the nearby extinct, Nevado de Colima, allow us to characterise the deposits and describe how the magma chemistry has changed over time.  Radiocarbon dating of charcoal fragments reveals the deposits span the past 30,000 years.

Field work involves generating stratigraphic sections with detailed descriptions of each eruption deposit, and collecting granulometry samples for tephra dispersion and eruption column height modelling; and samples for petrology and geochemistry.  Thin sections are looked at under the optical microscope, the scanning electron microscope (SEM) and electron microprobe (EPMA).  The mineralogy and textures are documented to identify magmatic processes such as changing temperatures, pressures and water contents in the storage system.

Samples are analysed for whole rock major and trace element geochemistry; as well as Sr and Nd isotopes.  The geochemical data allows us to distinguish the source melt and we can model assimilation, fractional crystallisation and magma mixing processes acting below the Colima volcanic complex.