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Thermal and gravity field implications of converting a mantle shear-wave velocity tomography of the South China Sea region to temperature and density

The seismic wave velocity configuration of the mantle provides constraints on its thermal and hence density structure, although the proposed methods of wave velocity conversion differ significantly. The V2RhoT_gibbs is a Python tool that allows converting mantle seismic velocities to temperature and density using a Gibbs free energy minimization algorithm applied to a defined mantle chemical composition to guarantee thermodynamic stability of the correspondingpressure (P) and temperature (T) dependent phase and mineral assemblages. Alternative methods, in contrast, start the conversion process with a pre-defined, P and T independent mineralogical composition, while yet other conversion methods involve a set of empirical equations. To better understand the differences between these conversion approaches, we have applied different methods to a shear-wave velocity tomographic model of the mantle below the South China Sea region. The resulting thermal fields are compared regarding the depth of the 1300 °C-isotherm which is a proxy of the lithosphere-asthenosphere boundary. In addition, we present the conversion results in terms of their respective gravity responses. This sensitivity analysis has important implications for better understanding the thermomechanical state of the lithosphere in the region.


Yan Li1, Judith Bott2, Scheck-Wenderoth Magdalena2, Pingchuan Tan3, Shaowen Liu4
1GFZ German Research Centre for Geosciences, Germany;Nanjing University, China; 2GFZ German Research Centre for Geosciences, Germany; 3Second Institute of Oceanography, Ministry of Natural Resources, China; 4Nanjing University, China
GeoBerlin 2023