First Paleointensity Data from the Mid-Neoproterozoic 300Myr void. Implications for Inner Core Nucleation Age?

Abstract:

The timing of inner core nucleation is a hugely significant event in Earth’s evolution and has been the subject of intense debate. The existence of an inner core provides additional power to the geodynamo, potentially translating into an increase in geomagnetic palaeointensity, thereby providing a signal of nucleation. Recent numerical dynamo simulations suggest nucleation occurred in the Neoproterozoic era; much younger than previously thought, however, a sparse record of palaeointensity data prevents any meaningful constraints from being applied. Here, we present results from 720 Ma dolerite dykes from the Franklin Large Igneous Province, which fall within a crucial 300 Myr gap in paleointensity records. The study uses three independent techniques on whole rocks from 11 sites in High Arctic Canada and Greenland, to produce virtual dipole moments ranging from 5 - 20 ZAm²; almost one order of magnitude lower than the present-day. We note that these weak-field results are in agreement with recent ultralow paleointensity data obtained from Ediacaran rocks formed ~150 Myr later and may support the claim that the geodynamo was on the brink of collapse in the Neoproterozoic prior to a young inner core formation date.