A local lithospheric structure model for Vietnam derived from a high-resolution gravimetric geoid
Résumé
High-resolution Moho and lithosphere-asthenosphere boundary depth models for Vietnam and its surrounding areas are determined based on a recently released geoid model constructed from surface and satellite gravity data (GEOID_LSC_C model) and on 3ʹʹ resolution topography data (mixed SRTM model). A linear density gradient for the crust and a temperature-dependent density for the lithospheric mantle were used to determine the lithospheric structure under the assumption of local isostasy. In a first step, the impact of correcting elevation data from sedimentary basins to estimate Moho depth has been evaluated using CRUST1.0 model. Results obtained from a test area where seismic data are available, which demonstrated that the sedimentary effect should be considered before the inversion process. The geoid height and elevation-corrected sedimentary layer were filtered to remove signals originating below the lithosphere. The resulting Moho and lithosphere-asthenosphere boundary depth models computed at 1ʹ resolution were evaluated against seismic data as well as global and local lithospheric models available in the study region. These comparisons indicate a consistency of our Moho depth estimation with the seismic data within 1.5 km in standard deviation for the whole Vietnam. This new Moho depth model for the study region represents a significant improvement over the global models CRUST1.0 and GEMMA, which have standard deviations of 3.2 and 3.3 km, respectively, when compared to the seismic data. Even if a detailed geological interpretation of the results is out of scope of this paper, a joint analysis of the obtained models with the high-resolution Bouguer gravity anomaly is finally discussed in terms of the main geological patterns of the study region. The high resolution of our Moho and lithosphere-asthenosphere boundary depth models contribute to better constrain the lithospheric structure as well as tectonic and geodynamic processes of this region. The differences in Moho depth visible in the northeast and southwest sides of the Red River Fault Zone confirmed that the Red River Fault Zone may be considered the boundary between two continental blocks: South China and Indochina blocks. However, no remarkable differences in lithosphere-asthenosphere boundary depth were obtained from our results. This suggests that the Red River Fault Zone developed within the crust and remained a crustal fault.
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