Multivectorial paleointensity determination from the Cordova Gabbro, southern Ontario

We report geomagnetic field intensities for the A (∼1000 Ma) and B (∼850 Ma) natural remanent magnetizations of the Cordova Gabbro of southern Ontario. We interpret A and B to be secondary thermal overprints produced during regional uplift and cooling following the Grenvillian Orogeny. Multivectorial A+B paleointensity data were analyzed using pairs of Arai diagrams for the separated A and B vectors. From 18 reliable A results and 15 reliable B results, we find paleofield values of 18.1±2.1 μT and 7.1±1.5 μT, respectively. The corresponding virtual axial dipole moments (VADMs) are (3.12±0.36) and (1.82±0.38)×1022 A m2, about 70% and 40% of the average Phanerozoic dipole moment based on data from 0.3–300 Ma. The Cordova data and other Precambrian paleointensities are generally within a range of approximately 0.5–1.5 times the Phanerozoic mean VADM. Three sets of paleofield values as a function of paleolatitude, including the Cordova data, support a dipole configuration for the Earth’s field in 25–150 Ma time windows around 2700 Ma, 1100 Ma, and 850 Ma.