Magnetization and age of ca. 544 Ma syenite, eastern Canada: Evidence for renewal of the geodynamo

The ca. 565 Ma Ediacaran geodynamo was highly unusual, producing an ultralow field 10 times weaker than present-day value of 8 x 10²² A m². A ∼5 times rise in field strength is seen in time-averaged single crystal paleointensity data of ca. 532 Ma Early Cambrian anorthosites of Oklahoma (USA). The field increase could record the onset of inner core nucleation predicted by thermal evolution and numerical dynamo models. Here, we examine the renewal of the geodynamo through zircon U-Pb geochronology and single crystal paleointensity studies of plagioclase from the Chatham-Grenville syenite intrusion in the Grenville Province (Canada). U-Pb data indicate a ca. 544 Ma age and Thellier single crystal paleointensity data yield field strengths of 2.3 ± 0.6 x 10²² A m². The new single crystal paleointensity data further support an increase in field intensity near the Ediacaran-Cambrian transition, consistent with latent heat of crystallization and release of light elements providing new energy sources to power the geodynamo upon the onset of inner core nucleation. Moreover, our new results suggest that plagioclase from syenites can yield valuable records of the geodynamo.