ABSTRACT: An Apatite Fission Track Transect across the Rockies at Jasper, Alberta: Preliminary Results of a Thrust Uplift Study

MCDONOUGH, M. R., G. S. STOCKMAL, and D. R. ISSLER, Geological Survey of Canada, Calgary, Alberta, Canada, and A. M. GRIST, and M. ZENTILLI, Dalhousie University, Halifax, Nova Scotia, Canada

Apatite fission track (AFT) ages and track lengths of samples collected along a transect from the western edge of the Rocky Mountain belt near Valemount, B.C., northeastward through the Main and Front ranges, and into the Foothills east of Jasper, Alberta, are used to constrain the timing of thrust versus erosional uplift of the foreland fold-thrust belt. Three basement gneisses from the western edge of the foreland yield uncorrected AFT ages of 15 to 20 Ma, substantially younger than published 44 to 48 Ma AFT ages for overlying cover rocks. However, length-corrected AFT ages for both studies cluster at about 55 Ma, suggesting the western edge of the foreland entered the track annealing window at the time. Mean confined track lengths for two basement samples (11.7 micrometer 1 sigma = 3.1; 12.3 micrometer, 1 sigma = 1.9) indicate significant partial annealing that may reflect slow cooling during erosion of 10-15 km of thrust overburden over the time represented by the corrected age. Alternatively, these data may indicate a volcanic and/or hydrothermal event associated with Miocene volcanism 75 km southwest. Because crustal extension following thrusting is not present at this latitude, the ca. 55 Ma corrected ages may represent the time of thrusting on young "out-of-sequence" thrusts in the western foreland. This is younger than the 58 Ma age reported for the initiation of extension farther south. Front Ranges and Foothills samples should yield uncorrected ages of thrust uplift, as the tectonic overburden was significantly less there. Thus, we predict a transition from erosion-related AFT ages in the west, to thrust-related ages in the east.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)