ORIGINS OF POLYMICTIC DIAMICT AT KIMA' KHO, NORTHERN BRITISH COLUMBIA, CANADA

Kima’ Kho is a partly eroded Pleistocene volcano that erupted on the Kawdy Plateau ~1.8 Ma (Ryane et al, in prep). At the northern end of the volcano, a polymictic diamict is exposed in a stream valley, located at 0375930E, 6542126N (UTM zone 9N) at an elevation of 1509 m. We are testing the hypothesis that the diamict is a glacial till deposited by a regionally extensive Pleistocene icesheet.

We have used a variety of field and laboratory techniques to characterize the diamict. The deposit was characterized in the field during July 2010. It extends roughly 200 m NE-SW and 20-25 meters vertically at its thickest point. Matrix and 50 clasts were sampled at random from the deposit, and trend and plunge measurements were taken for each clast (ave = 177 and 39°W with Std Dev of 11.96 and 26.43); no imbrication of the clasts was obvious in the field and the deposit was massive. It appears to unconformably overlie palagonitized lapilli tuff from Kima’ Kho. Clast dimensions were measured to document sphericity (Sneed & Folk, 1958: Ave. = 0.70, Std Dev = 0.10), and surface textures such as striations were documented. Twenty-one thin sections representing all internal textures were examined with a polarizing microscope, and 13 thin sections were analyzed by SEM-EDS. Six clasts of porphyritic volcanic rock were selected for geochemical analysis (analyses in progress), and XRD analysis was conducted to determine minerology of the diamict matrix (analysis in progress).

All of our results are consistent with the interpretation that the diamict is of regional origin. Clast sphericities are consistent with mainly transport within ice, as are the striations on some clasts. Mafic volcanic rocks are dominated by olivine porphyritic basalt, some of which can be differentiated based on the presence in the groundmass of magnetite only or magnetite and ilmentite. Preservation of glass in some volcanic clasts indicates the presence of younger volcanic rocks, some of which are of possible local origin. We are presently working to identify possible bedrock sources for all of the clasts to constrain the direction and distance of glacial transport.