Secular change of true polar wander over the past billion years

Abstract

The rate of movement of Earth’s solid shell relative to its spin axis, or true polar wander, depends on variations in mantle convection and viscosity. We report paleomagnetic and geochronologic data from South China that constrain the rate of rapid true polar wander (>5° per million years) between 832 million years and 821 million years ago. Analysis of the paleomagnetic database demonstrates secular change of true polar wander related to mantle cooling and thermal structure across supercontinent cycles. True polar wander rates are relatively muted with a partially insulated mantle during supercontinent assembly and accelerate as mantle thermal mixing reestablishes with supercontinent breakup. Decreasing true polar wander rate through the Neoproterozoic was succeeded by overall smaller variations in the Phanerozoic. We propose that Neoproterozoic extensive plate tectonic activities enhanced mantle cooling, giving rise to a reduction in mantle convective forcing, an increase in mantle viscosity, and a decrease in true polar wander rates into the Phanerozoic.

Reply to Mitchell and Jing: True polar wander alone is insufficient to drive measured Paleoarchean lithospheric motions

“…While TPW can attain rapid rates ( 1 , 6 , 7 ), this does not uniquely support its invocation here, as our measured rates are also consistent with plate motions. Rates alone are not diagnostic in the light of the poor fit, incongruent timescales, tectonic implications, and speculative underpinnings of purely TPW interpretations described above.…”

Paleoarchean plate motion: Not so fast

“… 2 except TPW rates from ref. 10 , where one outlier plots off-scale. Plate motion and TPW rates are over the same interval for direct comparison.…”

On pole position

“…Examples of such reference frames include those based on hotspot tracks (e.g., Müller et al, 1993;O'Neill et al, 2005;Torsvik et al, 2008a;Doubrovine et al, 2012), the locations of subducted slab remnants (van der Meer et al, 2010) or on a set of tectonics-based 'rules' (Müller et al, 2022). Combined or workings of the Earth's interior through geological time (e.g., Fu et al, 2022). Although being driven by processes in the Earth's interior, the reorientation of the solid earth relative to the spin axis may have profound impact on regional paleoclimate, paleoenvironment and extinction events (Evans, 2003;Yi et al, 2019;Jing et al, 2022).…”

“…The rate of TPW provides first-order kinematic constraints on the rate mantle convection, particularly on the velocity at which density anomalies, such as sinking lithospheric slabs, move through the Earth's mantle. Fu et al (2022) presented a compilation of paleomagnetically estimated TPW rates since the late Mesoproterozoic (~1100 Ma), proposing a direct link between the secular change of the TPW rate and the thermal structure and nature of convection in the mantle. Fast TPW (>1°/Ma) has often been inferred for pre-Pangean TPW, suggesting a different geodynamic regime that may correlate with the supercontinent cycle (e.g., Evans, 2003;Mitchell et al, 2014;Fu et al, 2022).…”

“…On geological timescales, the reorientation of the Earth's mantle and crust relative to the spin axis is driven by the redistribution of density anomalies within the Earth's mantle (e.g., Goldreich & Toomre, 1969;Gordon, 1987;Evans, 2003), such as sinking subducted slabs or rising mantle plumes. The magnitude and rate at which TPW occurs is primarily determined by the spatial distribution of excess masses and mass deficits and is ultimately controlled by the viscosity of the mantle (e.g., Sabadini & Yuen, 1989;Spada et al, 1992;Steinberger & Torsvik, 2010;Fu et al, 2022). Long-term (≥10 Ma) TPW is often kinematically quantified through the comparison of paleomagnetic reference frames, derived from apparent polar wander paths (APWPs) that track the motion of the spin axis relative to a tectonic plate, and mantle reference frames that record plate tectonic motions relative to the ambient mantle (e.g., Morgan, 1981;Harrison & Lindh, 1982a;Livermore et al, 1984;Andrews, 1985;Courtillot & Besse, 1987;.…”