Factors affecting the Pacific plate subduction towards and under the Changbaishan volcanic province since the Cenozoic: Insights from geodynamic modeling based on data assimilation

The origin of the Changbaishan volcanic province (CVP) has been considered to correlate with the subduction of the Pacific plate, so it is necessary to dynamically reconstruct the subduction history of the Pacific plate towards and beneath the CVP since the Cenozoic for probing the mechanism of the CVP. Many parameters affect slab subduction dynamics, so how to choose these parameters reasonably is the urgent issue to be solved during the reconstruction. A lot of analogue and numerical models have been used to study the effects of these parameters, but almost all of them have not considered a slab subduction history. In addition, seismic tomographic models have manifested that there is a high-speed anomaly zone extending over 1300 km within the mantle transition zone (MTZ) beneath the CVP. The zone is belived to consist of the Pacific slab in its eastern part and a segment of delaminated continental lithosphere (DCL) in its western part, bounded by approximately 120°E. A reasonable geodynamic model should reproduce both the Pacific slab and the DCL. Accordingly, in order to provide a reference for selecting geodynamic model parameters, we initially develop a series of three-dimensional (3D) thermochemical geodynamic models with data assimilation, in which several parameters are varied independently. These parameters encompass the Clapeyron slopes (γ₄₁₀ and γ₆₆₀) and thicknesses (δh₄₁₀ and δh₆₆₀) of the 410-km and 660-km discontinuities, the viscosities in the lower mantle (η_lw), the mantle transition zone (η_mtz) and the middle part of the lower mantle (η_mlw), seafloor age (t_o), the densities of the oceanic crust (representing it with the buoyancy ratio B₆) and asthenosphere (Δρ_asth), as well as the density jump across the 660-km discontinuity (Δρ₆₆₀). Subsequently, we primarily investigate how these parameters influence the westward movement distance, sinking depth, and structure of the Pacific slab, as well as whether geodynamic models incorporating these parameters can predict the high-speed anomaly zone. Finally, for reasonably reproducing the Pacific slab and the DCL beneath the CVP, we propose a suggested range of these parameters: γ₆₆₀ may lie within the range of −2.0 to −3 MPa/K; η_lw and η_mlw may range from 30 to 50 and should not exceed 75; B₆ may be set to −0.48, which corresponds to a mean density of 3.0 g/cm³ for the Earth's oceanic crust; the lower limit of the t_o may be adopted; η_mtz may be 1.0 to 2.5; Δρ_asth should adopt a reasonable and more negative value; and Δρ₆₆₀ may be set to a value of 10 to 15 %.