MAGNETITES FROM A NEW UNIDENTIFIED TEPHRA SOURCE, BANFF-NATIONAL-PARK, ALBERTA

Electron microprobe examination of glass-encased magnetites present within surficial volcanic ash deposits located in Banff and Jasper National Parks revealed five distinct magnetite populations. Three of the magnetite populations represented the Mazama, St Helens Y, and Bridge River volcanic units previously identified in this area of the Canadian Rocky Mountains, The remaining two magnetite groups are characterized by glass-encased magnetites which have titanium oxide concentrations of 11.59 and 10.33%, values considerably higher than those characterstic of either Mazama, St Helens Y, or Bridge River volcanic units. The high-titanium magnetites are of unknown provenance, and although the section provided no means for dating these volcanic groups, their distribution within the section suggests that they are older than Bridge River, and one group many predate Mazama.-Authors