Abstract
High-resolution Moho and lithosphereâasthenosphere 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 3ÊčÊč 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 lithosphereâasthenosphere boundary depth models computed at 1Êč 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 lithosphereâasthenosphere 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 lithosphereâasthenosphere boundary depth were obtained from our results. This suggests that the Red River Fault Zone developed within the crust and remained a crustal fault.
Highlights
The Vietnam region, lying on the southeast part of the Eurasian tectonic plate, has a complex tectonic history inherited from the tectonic evolution of Southeast Asia
Where zc is the depth of the crust-mantle boundary (Moho), zL is the depth of the lithosphereâasthenosphere boundary (LAB), Ïc is the mean density of the crust, Ïm is the mean density of the lithospheric mantle, Ïw is the density of the sea water, Ïa is the density of the asthenosphere, L0 is the depth of the free asthenospheric level, and E is the elevation
Moho and LAB depth estimation for the test area The selected test area is located in Central Eurasia where a Moho depth model was determined by Robert et al (2017) using geoid height and elevation data derived from EGM2008 and ETOPO1
Summary
The Vietnam region, lying on the southeast part of the Eurasian tectonic plate, has a complex tectonic history inherited from the tectonic evolution of Southeast Asia. The Hoang Lien Son Mountain Range is the highest relief of this region, with its Fansipan peak at the height of about 3,140 m above sea level This northern part of Vietnam has a complicated tectonic setting, dominated by active faults, such as the Red River Fault (RRF), Chay River Fault (CRF), Lo River Fault (LRF)âall within the Red River Fault System (RRFS), Dien Bien Phu Fault (DBPF), Da River Fault (DRF), Ma River Fault (MRF), and Son La Fault (SLF) (Fig. 1a, b). The RRFZ, located in the center of the northern part of the study region, extends 1000 km from the eastern Himalayas through southernmost China to northern Vietnam and is considered to be mechanically connected with the IndianâEurasian collision This fault zone is considered as a pure crustal structure (Jolivet et al 2001; Searle 2006). Such earthquakes have caused heavy damage in the northwest as well as offshore from central Vietnam
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