Lithospheric Driving Forces From Recent Global Density Models

The motion and deformation of the lithosphere result from forces and stresses that are driven by lateral variations in gravitational potential energy (GPE). In turn, GPE variations derive from lateral differences in the thermal or lithological density distribution. The recent development of global lithospheric models allows us to take a step forward towards consistent estimates of Horizontal Gravitational Tractions (HGTs) that arise from lateral gradients in GPE. We find that lithospheric model LithoRef18 [Afonso et al. 2019] yields unrealistic GPE and HGT results. Our preferred HGT field uses lithosphere model WINTERC-G [Fullea et al. 2021] to incorporate horizontal GPE gradients with a laterally variable Lithosphere-Asthenosphere Boundary (LAB). The azimuth of HGTs is most strongly correlated with the azimuth of topographic gradients, while the HGT magnitudes correlates best with topography gradient magnitude for HGTs larger than 10MPa. The most significant HGT magnitudes, exceeding 100 MPa, occur along the edges of the Andes and Tibetan plateaus. Tractions in cratonic regions are generally low, except where surface, Moho, or LAB topology gradients are large. Our attempt to isolate the HGT of the overriding plate yields moderate oceanward HGTs in the forearc along all convergence zones, which may be interpreted as trench suction. We explore the sensitivity of the HGT to classical integration limits of the deepest Moho or 100km depth to find that HGT magnitudes are markedly different and that HGT directions are relatively insensitive to integration depth.

 

Afonso, J.C., Salajegheh, F., Szwillus, W., Ebbing, J. Gaina, C. (2019), A global reference model of the lithosphere and upper mantle from joint inversion and analysis of multiple data sets, Geophys. J. Int., 217(3), 1602–1628.

Fullea, J., Lebedev, S., Martinec, Z., Celli, N.L. (2021), WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data, Geophys. J. Int., 226(1), 146–19.