Paleomagnetism and Deformation of the Quottoon Pluton, British Columbia

Abstract

In this study, we are using directions of magnetization to determine how the 60 my old Quottoon pluton (Coast Mountains, British Columbia) has deformed. In May 1998, 119 oriented core samples from 17 sites were collected. In general, the remanence of the samples was very resistant to alternating field demagnetization up to 100mT and thermal demagnetization to 610 deg C, strongly suggesting hematite as the carrier of the magnetization. Of 17 sites, 9 show downward magnetization directions (normal polarity) and 8 have upward directions (reverse polarity). When compared to a reference direction for stable North America, all reverse sites have shallow inclinations and apparent counter-clockwise rotations. On the other hand, most normal sites lie close to the expected direction. Apparently, the Quottoon pluton has undergone considerable deformation at temperatures below 680 deg C.