Collaborative Research: Quantifying the Dynamics of Asia Using GPS, Geologic and Shear-Wave Splitting Data, and Large-Scale Flow Models

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This work aims at improving the understanding of the dynamics of continental deformation, one of the major unresolved -- and highly debated -- issues of the "plate tectonics era". Two end-member models dominate the scene. In the first one, the lithosphere is treated as a set of rigid "blocks" separated by finite zones of deformation, whose motions are controlled by forces applied at the edges of the blocks. In the second one, the lithosphere is treated as a viscous continuum and deformation is driven by both relative plate motions and buoyancy forces resulting from gravitational potential energy (GPE) gradients within the lithosphere.Asia is the largest zone of diffuse deformation on the surface of the Earth. As such, it is a natural laboratory to study how and why continents deform. Active deformation in Asia is fairly well documented geologically. This project incorporates a new geodetically-derived velocity and strain rate field that covers the entire continent. A key feature of this velocity field is the east- to southeastward motion of the entire eastern portion of central Asia from east of Baikal south to the Sunda block. This feature is not reproduced by block models where deformation is solely driven by the collision of a "rigid" Indian indenter into the Asian lithosphere. More comprehensive thin sheet modeling efforts that account for buoyancy forces and inter-plate coupling, are still not sufficient to explain this feature.This study is examining the driving forces responsible for continental deformation in Asia, with a particular emphasis on the eastward migration of the eastern margin observed in the GPS data by (1) combining the most recent GPS solutions and geologic data in Asia to determine a complete kinematic strain rate and velocity field over the entire continent, (2) computing the contribution of GPE variations (using lithospheric models) and of tractions at the base of the lithosphere (using mantle flow models derived from global tomography), (3) using the kinematic data and stress fields resulting from GPE gradients and basal traction to estimate boundary stresses and, eventually, determining a consistent set of forces that explain the geodetic observations. Additionally, shear-wave splitting observations in conjunction with the surface kinematic field are being used as an independent estimate, to directly solve for the direction of flow beneath East Asia in order to understand the origin of the eastward migration.Among the broader impacts of this work are support for an early career female researchers, support and training of a graduate student, and a female undergraduate.