The upper mantle geoid: Implications for continental structure and the intraplate stress field

Abstract

We use the fact that geoid anomalies are directly related to the local dipole moment of the densitydepth distribution to help constrain density variations within the lithosphere and the associated tectonic stresses. The main challenge with this approach is isolating the upper mantle geoid contribution from the full geoid (which is dominated by sources in the lower mantle). We address this issue by using a high-pass spherical harmonic filtering of the EGM2008-WGS84 geoid to produce an "upper mantle" geoid. The tectonic implications of the upper mantle are discussed in terms of plate tectonics and intraplate stresses. We find that globally there is about a 9 meter geoid step associated with the cooling oceanic lithosphere that imparts a net force of ~2.5x10 12 N/m in the form of "ridge push" -a magnitude that is consistent with 1-d models based on first-order density profiles. Furthermore, we find a consistent 6 meter geoid step across passive a continental margin which has the net effect of reducing the compressive stresses in the continents due to the ridge force. Furthermore, we use the upper mantle geoid to reevaluate the tectonic reference state which previously studies estimated using an assumption of Airy-based isostasy. Our evaluation of the upper mantle geoid confirms the near equivalence of the gravitational potential energy of continental lithosphere with an elevation of about 750 meters and the mid-ocean ridges. This result substantiates early conclusions about the tectonic reference state and further supports the prediction that continental regions are expected to be in a slightly extensional state of stress.

Tectonic subsidence, geoid analysis, and the Miocene-Pliocene unconformity in the Rio Grande rift, southwestern United States: Implications for mantle upwelling as a driving force for rift opening

“…The ratio between the average elevation of the Rio Grande rift and the lithospheric geoid provides information about the compensating mechanism for the topography, and therefore the degree to which dynamic uplift from the upper mantle is supporting the topography. Geoid height anomalies for isostatically compensated regions can be directly related to the local density dipole moment, which can be used to evaluate the subsurface distribution of mass associated with various surface features (see review and discussion in Coblentz et al, 2015). Given the important role that density variations in the uppermost mantle play in rift dynamics, it is of primary interest to constrain the depth of the density distributions that control the lithospheric geoid.…”

Deformation Analysis in the Barents Sea in Relation to Paleogene Transpression Along the Greenland‐Eurasia Plate Boundary

“…Other contributions have been neglected. Those contributions include horizontal gradient of GPE (Coblentz et al, 2015; Ghosh et al, 2008; Schiffer & Nielsen, 2016), and horizontal tractions at the base of the lithosphere related to mantle convection (Ghosh et al, 2008).…”

“…Lithospheric GPE gradients in the North Atlantic, arising from elevated areas (such as mid-ocean ridges and Iceland), and lithosphere density contrasts, as well as from radial tractions (dynamic uplift) caused by the Iceland plume impingement and mantle motions in the North Atlantic, may contribute to intraplate 10.1029/2020TC006172 Tectonics deviatoric stresses and deformation at North Atlantic continental margins, including the Barents Sea shelf (Coblentz et al, 2015;Doré et al, 2008;Schiffer & Nielsen, 2016).…”

Gravitational Potential Energy per Unit Area as a Constraint on Archean Sea Level

“…When they are filtered out, remaining geoid heights over spreading centers and low continents are similar (Coblentz et al, ; Doin et al, ; Ghosh et al, ; Turcotte & McAdoo, ). Coblentz et al () referred to this as the lithospheric geoid. Doin et al () and Turcotte and McAdoo () used this match of geoid heights to estimate a value of for stable continents and cratons.…”