Alteration of basaltic glasses from north-central British Columbia, Canada

The process of palagonitization in basaltic glasses from Pleistocene subglacial volcanics in the north-central British Columbia, Canada, is examined on the basis of results obtained from samples from three volcanoes located in the Tuya Range of Cassiar mountains: Ash Mountain, Southern Tuya, and Tuya Butte. The compositional changes from glass to palogonite, in particular with respect to Al content are described. Results of this study suggests that palagonitization is an isovolumetric replacement process in the British Coumbia hyaloclastites, in which glass is replaced by amorphous colloidal palagonite; the process is explained by the precipitation of insoluble material as critical nuclei under the conditions of supersaturation in the near-glass environment.