Using thermochronometry and low‐temperature demagnetization to accurately date Precambrian paleomagnetic poles

Abstract

Dating magnetizations in Precambrian rocks is increasingly important in the attempt to unravel Precambrian plate configurations and supercontinent assemblages. We used low‐temperature demagnetization and modern thermochronometric methods to dissect a multicomponent magnetization of the Glamorgan Gabbro, Ontario, previously studied by Buchan and Dunlop [1976] and Berger and York [1981]. We found that the H bA component is a primary thermoremanent magnetization carried by single‐domain magnetite. The new paleomagnetic pole position (32.6°S latitude, 141.9°E longitude) is not significantly different from the published pole; however, the cooling history suggests that the 1015±15 Ma magnetization age is older than previously thought (980 Ma). The new age produces a better fit in Rodinia supercontinent reconstructions. The refined Hb B pole (29.9°N latitude, 169.9°E longitude) is carried by multidomain‐type magnetite and pyrrhotite. A possible ∼175°C thermal event at ∼600 Ma recorded by K‐feldspar could be responsible for remagnetizing the multidomain grains. The new age for Hbß is 220 m.y. younger than the previous estimate, raising questions concerning the ages of similar poles from the Canadian Grenville Province.