Low-temperature cooling history of the Shuswap metamorphic core complex, British Columbia: constraints from apatite and zircon fission-track ages

Abstract

Nine zircon and 18 apatite fission-track ages are used to determine the low-temperature cooling history of part of the Shuswap metamorphic core complex of the Canadian Cordillera. The zircon ages range from 54 to 38 Ma and the apatite ages from 49 to 28 Ma. These ages reveal a similarity in cooling histories across the Shuswap units until temperatures of ~250°C were reached at about 45 Ma. From this time onwards, the regional cooling pattern within the core complex was controlled by the relative movements on two normal faults, the Victor Creek fault and the Columbia River fault. Cooling since 45 Ma was variable, depending on the structural level of the sample. On this basis four thermotectonic units are defined. These units are controlled by normal faults that crosscut the lithological units of the core complex and reflect the latest stage of its evolution.

The thermal–mechanical evolution of crustal orogenic belts at convergent plate boundaries: A reappraisal of the orogenic cycle

“…In regions marked by the formation of intermontane and back-arc basins, normal faults are superimposed on thrusts. In the North American Cordilleran metamorphic core complexes (Coney, 1980), low-angle detachments are cross-cutting suture zones and major thrusts and are themselves cross-cut by high-angle normal faults (Parrish et al, 1988;Johnson and Brown, 1996;Vanderhaeghe et al, 1999bVanderhaeghe et al, , 2003bLorencak et al, 2001). Further south, in the Basin-and-Range region, widespread extension is accommodated by a large number of highangle normal faults defining a succession of horsts and grabbens (Wernicke, 1992;Liu, 2001).…”

Low‐temperature thermochronologic record of Eocene migmatite dome emplacement and late Cenozoic landscape development, Shuswap core complex, British Columbia

“…Very slow cooling of these rocks (1-3°C/Ma) until the Eocene was determined by hornblende, biotite, and muscovite K-Ar and 40 Ar/ 39 Ar methods [e.g., Colpron et al, 1996]. An apatite fission track (AFT) age of 66.7 ± 9.6 Ma from the hanging wall of the Eagle River-Okanagan detachment fault [Lorencak et al, 2001] indicates that the upper unit cooled before the formation of the Shuswap MCC. The K-Ar method was used to date rhyolitic to basaltic volcanic rocks in the extensional basins of the upper unit.…”

Brittle faulting in the Thor–Odin culmination, Monashee complex, southern Canadian Cordillera: constraints on geometry and kinematics

“…A countryrock muscovite from the contact of a dyke yielded an age of 48.4 ± 0.3 Ma, which they interpret as the contact metamorphic age and thus emplacement age of the dyke. Lorencak et al (2001) interpret apatite and zircon fission-track data in the region to suggest that the Victor Creek Fault was active after 45 Ma.…”