Explaining the Kinematics of the Kootenay Arc: a Paleomagnetic Analysis

Posted May 11th, 2010 at 3:03 pm.

Jordan Conan

Mentor: Professor A. Weil

Many mountain (orogenic) belts are curved like a bow in map view (e.g., the Appalachians, Himalayas, Alps, etc.). These orogenic belts can fall under one of three kinematic (history of deformation and motion) classifications: the belt was initially curved and experienced no rotation (primary arc); the belt was originally linear and experienced rotation (orocline); the belt acquired it’s rotation as it was being formed, or was initially bent and experienced further rotation (progressive arc). To date, the only robust and quantitative method of determining vertical-axis rotations is paleomagnetism (the study of the Earth’s ancient magnetic field as it is recorded in the rock record). When combined with structural and geologic data, paleomagnetic data is an extremely useful tool for constraining the kinematics of a curved orogen. Our study concerns the curvature of the Kootenay Arc in British Columbia, Canada. The Kootenay Arc, situated in the Canadian Rockies, is thought to be one of a number of terranes that have collided with what was once the western margin of North America. Previous papers have described this arc as both an orocline and as a primary arc. There has, however, been no paleomagnetic study of this region. Ferromagnetic minerals present in most rocks align themselves with the Earth’s magnetic field, and as a result record the rock’s paleo-latitude as well as the rock’s orientation with respect to the Earth’s spin-axis at the time of magnetization acquisition. If the ChRM (Characteristic Remanant Magnetizion) of a rock is acquired prior to the deformation that generates the orogenic belt, then kinematic classification of the belt should be relatively straight forward. The ChRM of a primary arc would show no rotations, the ChRM of an orocline would show a one-to-one correlation between rotations and map-view curvature, and the ChRM of a progressive arc would show a correlation between structural trend and magnetization that is less than one-to-one (orocline), but greater than zero (primary arc). Professor Arlo Weil, Alexi Ernstoff, and I plan to obtain samples from the Kootenay Arc that can be used for paleomagnetic analysis. The eventual goal of this project is to use paleomagnetism to help explain the kinematics of the Kootenay Arc, and thus broaden our understanding of orogenic evolution in general and the evolution of the Rocky Mountains in specific.

Filed under: 2007,Conan, Jordan,Weil, Dr. Arlo by Ann Dixon

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