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

Dating magnetizations in Precambrian rocks is increasingly important in the attempt to unravel Precambrian plate configurations and supercontinent ass emblages. We used low-temparature demagnetization and modern thermochronome tric methods to dissect a multicomponent magnetization of the Glamorgan Gab bro, Ontario, previously studied by Buchan and Dunlop [1976] anti Berger an d York [1981]. We found that the Hb(A) component is a primary thermoremanen t magnetization carried by single-domain magnetite. The new paleomagnetic p ole position (32.6 degrees S latitude, 141.9 degrees E longitude) is not si gnificantly different from the published pole; however, the cooling history suggests that the 1015 +/- 15 Ma magnetization age is older than previousl y thought (980 Ma). The new age produces a better fit in Rodinia superconti nent reconstructions, The refined Hb(B) pole (29.9 degrees N latitude, 169. 9 degrees E longitude) is carried by multidomain-type magnetite and pyrrhot ite, A possible similar to 175 degrees C thermal event at similar to 600 Ma recorded by K-feldspar could be responsible for remagnetizing the multidom ain grains, The new age for Hb(B) is 220 m.y. younger than the previous est imate, raising questions concerning the ages of similar poles from the Cana dian Grenville Province.