Paleosecular variation of brunhes age lava flows from British Columbia, Canada

Abstract

Brunhes age lava flows have been sampled for paleosecular variation studies from several volcanic fields of southern British Columbia (Silverthrone, Garibaldi Lake, Mt. Meager, Clearwater‐Wells Gray Park and Kelowna area). A total of 52 lava flows were sampled and 7 to 10 samples were drilled at each site. Previous radiometric studies indicate that the ages of these lava flows range from 2.3 to 760 Ka. Stepwise thermal demagnetization (14 to 21 steps) was carried out for all the samples in each site and AF demagnetization was performed on one sample per site. Forty‐five sites were selected based on rigorous criteria (α95 ≤ 5°) to calculate a mean direction (D = 356.9°, I = 70.2°, α95 = 2.8°) that is statistically indistinguishable from the direction of the dipole field at the area (I = 68.3°). Virtual geomagnetic poles (VGPs) do not show the far‐sided effect and the angular standard deviation is 17.5°, a value in agreement with the paleomagnetic field dispersion for that latitude. These high quality results are expected to improve the time averaged field (TAF) and secular variation models.