Testing links between mantle plumes and true polar wander

Thursday, 18 December 2014
Athena E Eyster, Richard J O'Connell and Francis A Macdonald, Harvard University, Cambridge, MA, United States
True polar wander (TPW) is the motion of the crust and mantle relative to the spin axis due to changes in the Earth’s moment of inertia. Paleomagnetic studies assume that plate tectonic speeds have been relatively constant through time, and thus observations of large, rapid movements in paleomagnetic poles have been attributed to true polar wander. A large TPW event would result in a dramatic repositioning of the continents relative to the equatorial oceanic bulge and the ecliptic, causing changes in relative sea level, potentially altering the Earth’s global oceanic circulation patterns and biogeochemical cycles. Mantle density anomalies such as plumes, which are linked to large igneous provinces, can affect Earth’s moment of inertia and cause TPW. It has been suggested that a superplume triggered a ca. 800 Ma episode of large scale TPW (Li et al., EPSL, 2004). Additionally, the mantle plume associated with the ca. 615-535 Ma Central Iapetus Magmatic event and rifting of Laurentia’s eastern margin has been proposed as a possible trigger for TPW (Kirschvink et al., AGU, 2005). Here we combine plume advection and rotational dynamics models to investigate the hypothesis that Neoproterozoic TPW events were initiated by mantle plumes. For each plume event, we estimate plume radius and current location of the plume center from published geologic observations. The location of plume center is rotated using paleomagnetic data to obtain the paleolatitude of the plume at the time of eruption. Plumes consistent with the estimated sizes are advected from the core mantle boundary. The spherical flow fields are calculated using the propagator matrix method and advection is done via a flux-corrected transport algorithm. Using the output from the advection model and the estimated paleolatitude of eruption, the TPW is calculated using the quasi-fluid approximation to the nonlinear rotational dynamics equations. For each event investigated, we explore variations due to changing the viscosity contrast between the upper and lower mantle, adding a lithosphere, and changing the reference shape. The model-generated TPW is compared to paleomagnetic data. Current results suggest that the Ediacaran TPW seen in the paleomagnetic record may be consistent with that expected from the mantle plume associated with the Central Iapetus Magmatic event.