A Gravity-Derived Moho Model for the Sikhote Alin Orogenic Belt

Analysis of the available Moho models for the Sikhote Alin region revealed significant discrepancies between them both in depth for individual sites and isolines over the entire area of the orogenic belt. In this study, results of the two-dimensional power spectrum analysis of the gravity field based on a digital model of the Bouguer gravity field were used to calculate the crustal thickness (Moho depth). The data from seven seismic profiles were employed to adjust the new model. The new model and its correlation with structural and geological data allowed the following conclusions to be made. (1) The span of Moho depth variations for the southern part of the continental Far East of Russia is just over 18 km, with extreme values of 42.4 and 24.0 km. The Moho is deepest (41–42 km) beneath mountain ranges and massifs: Sikhote Alin in the east and Yam Alin and Aesop in the north-west. The Moho is most shallow (27–30 km) beneath the sedimentary basins Khanka, Partizan-Sukhodol, Suifun in the south, Middle Amur and Lower Amur in the central part of the study area, and Upper Zeya and Uda in the north-west. (2) Correlation of the Moho estimates derived from the Airy model and the power spectrum of the Bouguer gravity field shows significant positive correlation. The Moho depths practically coincide over 11% of the area, with a difference of ± 5%. The Moho depth discrepancies are in the range of 5–15% over 48% of the study area, and over the rest of the study area (41%), discrepancies are in the range of 15–30%. (3) A comparison between the new gravity Moho model and the geological and structural data shows that the model is highly correlated with the development of Cretaceous–Early Eocene orogenic and post-orogenic granitoid massifs and Cretaceous–Pliocene extrusive igneous rocks. The former geographically coincide with two linear zones in the Moho relief with depths of more than 35 km, and the latter with the Mesozoic–Cenozoic sedimentary basins and the East Sikhote Alin volcano–plutonic belt.