The Crust and Upper Mantle Structure of the Southern Sikhote Alin along the Profile Dal’nerechensk–Roshchino–Plastun from Magnetotelluric Sounding Data

Resumo

Magnetotelluric soundings (MTS) are carried out in a broad frequency range from 10⁴ to 10^–3 Hz at a total of fifty-five sounding sites spaced about 5 km apart along the profile Dal’nerechensk–Roshchino–Plastun across the strike of the Sikhote Alin Orogenic Belt (SAOB). Based on the results of data interpretation, the crust and upper mantle geoelectric section is constructed down to a depth of 150 km. The section shows the crust of variable thickness between 20 and 40 km with a resistivity higher than 1000 Ohm m, which consists of different-resistivity blocks bordered by subvertical and inclined low-resistivity zones, from tens to a few hundreds of Ohm m. Three abnormal-resistivity zones are revealed in the crust and upper mantle. The upper mantle structure is nonuniform. Beneath the western and eastern parts of the SAOB, the lowest resistivity values are observed at 40–80 km depths. A high-resistivity zone of 300–500 Ohm m, stretching in the westerly direction from the coast beneath the Khanka superterrane, is identified in the 80–150 km depth range. This area is treated as remnants of the plate of an ancient subduction zone; two low-resistivity canals are distinguished here, which are associated with a slab-window. The results obtained for the northern and southern parts of the SAOB are compared and their similarities and dissimilarities are ascertained.