Constraining Earth's nonlinear mantle viscosity using plate-boundary resolving global inversions

• 成果类型: Article
• 署名作者: Hu, Jiashun; Rudi, Johann; Gurnis, Michael; Stadler, Georg
• 署名单位: Southern University of Science & Technology; Virginia Polytechnic Institute & State University; California Institute of Technology; New York University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-13031
• DOI: 10.1073/pnas.2318706121
• 发表日期: 2024-07-09
• 关键词: joint inversion; subduction; FLOW; convection; MODEL; tectonics; rheology; deformation; lithosphere; EVOLUTION

摘要

Variable viscosity in Earth's mantle exerts a fundamental control on mantle convection and plate tectonics, yet rigorously constraining the underlying parameters has remained a challenge. Inverse methods have not been sufficiently robust to handle the severe viscosity gradients and nonlinearities (arising from dislocation creep and plastic failure) while simultaneously resolving the megathrust and bending slabs globally. Using global plate motions as constraints, we overcome these challenges by combining a scalable nonlinear Stokes solver that resolves the key tectonic features with an adjoint-based Bayesian approach. Assuming plate cooling, variations in the thickness of continental lithosphere, slabs, and broad scale lower mantle structure as well as a constant grain size through the bulk of the upper mantle, a good fit to global plate motions is found with a nonlinear upper mantle stress exponent of 2.43 +/- 0.25 (mean +/- SD). A relatively low yield stress of 151 +/- 19 MPa is required for slabs to bend during subduction and transmit a slab pull that generates asymmetrical subduction. The recovered longterm strength of megathrusts (plate interfaces) varies between different subduction zones, with South America having a larger strength and Vanuatu and Central America having lower values with important implications for the stresses driving megathrust earthquakes.