Using Glaciovolcanic Processes and Products at the Mount Edziza Volcanic Complex (MEVC), British Columbia, Canada to Constrain Paleo-Ice Conditions: Initial Results

The Mount Edziza Volcanic Complex (MEVC) of the northern cordillieran volcanic province (NCVP) erupted basaltic, trachytic and rhyolitic effusive and explosive products in a wide variety of subaerial and subaqueous environments from about 8Ma to about 2000yrs BP. Souther (1992) suggested that several eruptive products were emplaced in a sub-ice or ice-contact environment; an interpretation confirmed by our investigations in 2006. Glaciovolcanic rocks at the MEVC are significant because they record evidence of ice presence and thickness in a region for which there is very little data on ice conditions prior to the most recent glaciation Several areas of likely basaltic and trachytic glaciovolcanic products were examined in detail on the western side of MEVC, in order to confirm their glaciovolcanic nature, and to ultimately better constrain paleo-ice presence and thickness. Our initial results presented here are focused on documenting the processes and products in detail. For example, a sequence of basaltic subaqueous lavas erupted from Tennana Cone, displayed spectacular evidence for the role of sub-ice bedrock topography on the geomorphology and structure of such lava flows. Proximal flows were emplaced in a sheet-like form as both pillow and lobate flows with mounding of pillow lavas at the crest of sub-ice cliffs (ie at contact with thicker ice). Pillow lavas were emplaced in sinuous drainage tunnels at the base of the cliffs. Trachytic lava flows and domes form an important part of the MEVC sequence and many also display evidence of ice-contact or sub-ice emplacement. In particular, Triangle Dome on the northwestern side of the MEVC displays a pattern of columnar cooling joints that indicates that it was emplaced as several very steep-sided domes in a sub-ice environment. Geochronology, geochemistry and volatile analysis of basaltic and trachytic glass from these and several other localities are currently ongoing, and with detailed study of the products, will help us constrain the paleo-ice thicknesses during the Pleistocene at the MEVC. We hope that the methods we develop for constraining paleo-ice conditions can be used at other glaciovolcanic centers and perhaps become part of a standard palaeoclimatological toobox for terrestrial environments