Aspects of Cordilleran Geothermal History from Fission-Track Analysis in the Lewis and Coleman Overthrust Plates, Southwestern Alberta and Southeastern British Columbia

OSADETZ, KIRK G., Institute of Sedimentary and Petroleum Geology, Calgary, Alberta, Canada, BARRY P. KOHN and SHIMON FEINSTEIN, Ben Gurion University of the Negev, Beer Sheva, Israel, and RAYMOND A. PRICE, Queen's University, Kingston, Ontario, Canada

Apatite fission-track data from pre-Tertiary rocks in the southern Canadian Front Range and Foothills are younger than their stratigraphic ages, indicating thermal setting. Limited confined track-length distribution data indicate rapid cooling from the total annealing zone at about the age recorded. There appears to be a consistent difference between apatite ages of the Lewis plate (64-80 Ma) and the underlying Coleman plate (46-59 Ma). Zircon single-grain fission-track age distributions in both overthrust plates show a long tail of scattered ages but with a distinctive signal, indicating thermal resetting during the Cretaceous or Tertiary. The age of the thermal zircon fission-track resetting signal overlaps or is only slightly older than corrected apatite fission-track ages, in thei respective thrust plates. Between 70 and 80 Ma, Lewis plate samples experienced temperatures higher than those required for total apatite annealing and were subsequently cooled very rapidly through apatite fission-track annealing to apatite fission-track stability temperatures. The Coleman plate data suggest an analogous thermal history but occurring 15-20 Ma later, during the early Tertiary. Oligocene sediments in the Flathead graben have apatite fission-track ages and track lengths like that of the Lewis plate, the known source of these sediments, indicating no significant postorogenic thermal events.

AAPG Search and Discovery Article #91010©1991 AAPG Rocky Mountain Section Meeting, Billings, Montana, July 28-31, 1991 (2009)