Geodynamic and tectonic processes during the Archean remain enigmatic and hotly debated. Paleomagnetism can quantify the rates timing of tectonic processes. We discuss recent paleomagnetic datasets that we have measured from late Paleoarchean rocks in the East Pilbara Craton, Western Australia, which have shown that the East Pilbara experienced substantial surface motions during ~3.3-3.2 Ga (Brenner et al., 2020; Brenner et al., 2022). These surface motions occurred at rates of ~0.5°/Myr (or ~6 cm/yr) and were sustained for many tens of Myr, consistent with plate tectonic motions but inconsistent with motions of a stagnant-lid. The data also reveal the oldest documented geomagnetic reversal, indicating that the geodynamo was likely dominantly-dipolar like it is today. Together, these results suggest a geodynamically-mature Paleoarchean Earth from the surface to the core. Importantly, lessons learned from these studies have given us a robust toolkit, including magnetic microscopy and radiometric dating, for understanding the mechanism and timing of magnetizations by tying them to specific mineralization reactions and hydrothermal alteration events. This paves the way for future paleomagnetic work in Archean rocks, in which seafloor hydrothermal systems were especially common. We also discuss ongoing work to refine and extend the geodynamic record further into deep time.

Reference(s)

Brenner, AR, Fu, RR, Evans, DAD, Smirnov, AV, Trubko, R and Rose, IR 2020, Paleomagnetic evidence for modern-like plate motion velocities at 3.2 Ga: Science Advances, v. 6. 

Brenner, AR, Fu, RR, Kylander-Clark, ARC, Hudak, GJ and Foley, BJ 2022, Plate motion and a dipolar geomagnetic field at 3.25 Ga: PNAS, v. 119, n. 44.