HR: 0830h
AN: GP31C-0758 INVITED     [PDF]
TI: The Paleomagnetic Effects of Reheating the Ecstall Pluton, British Columbia
AU: * Hollister, L S
EM: linc@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08540 United States
AU: Hargraves, R B
AF: Department of Geosciences, Princeton University, Princeton, NJ 08540 United States
AU: James, T S
EM: james@pgc.nrcan.gc.ca
AF: Geological Survey of Canada, Pacific Geoscience Center, Sydney, BC V8L 4B2 Canada
AU: Renne, P R
EM: prenne@bgc.org
AF: Berkeley Geochronology Center, Ridge Road, Berkeley, CA 94709 United States
AB: Current interpretations of paleomagnetic data of plutons from the western Canadian Cordillera vary from thousands of kilometers of cross-latitudinal transport, to in situ tilting, to post-intrusion folding. The Ecstall pluton of British Columbia is ilmenohematite-bearing, and it has a progressive steepening of inclination of magnetic remanence vectors from 16o to 81o [1] between 24 and 12 km west of a thermal boundary with the Coast Mountains batholith (CMB). The CMB was at 700-800oC between 60 and 52 Ma. Our heat flow calculations show that the thermal effects of the CMB on the adjacent 91 Ma Ecstall pluton were enough to reset the thermal chemical remanent magnetisation (TCRM), which occurs at less than 390oC [2]. Reheating to the temperatures necessary for TCRM is supported by K/Ar and Ar/Ar cooling dates on hornblende and biotite. Thus, the progressive shallowing of NRM vectors is attributed to reheating of the Ecstall pluton by the Coast Mountains batholith, following post-solidification cross-latitudinal transport of the pluton. Much of the controversy concerning the amount of translational displacement of the coastal terranes of British Columbia prior to 60 Ma hinges on the interpretation of discordant magnetizations from plutons that may have cooled slowly after emplacement in the mid to lower crust, as was the case for the Ecstall pluton. Many of these plutons contain ilmenohematite as an accessory magnetic phase. Our interpretation for the acquisition of NRM in the Ecstall pluton may have far-reaching implications for understanding of the enigmatic discordant paleomagnetic directions reported from plutons of the western Canadian Cordillera.
DE: 1519 Magnetic mineralogy and petrology
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1533 Remagnetization
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting