Tectonic Fragmentation and Geodynamic Regime of Elbrus and Kazbek Volcanoes (Central Caucasus, Russia): Results of the Deep Geophysical Research

Abstract

A comprehensive analysis of instrumental data was carried out to establish indicators of the geodynamic conditions of interaction between the Scythian Plate and the collage of southern plates; and to determine the type and kinematics of the Main Caucasian Thrust and the nature of volcanoes in the North Caucasus. In terms of structure and tectonics, the studies were conducted within the alpine structure of the Greater Caucasus, and they equally characterize both of its first-order structures: the folded-block uplift of the Main Range and the North Caucasian regional massif. In the kinematics of the Main Caucasian Thrust and volcanoes of the North Caucasus, there are no subduction elements. The absence of correspondence of the Main Thrust to the Benioff zone, and, conversely, its similarity to listric faults and shallow-focus volcanic centers are more consistent with a collisional geodynamic situation. Geological and geophysical sections along the network of regional profiles of deep geophysical studies in Ciscaucasia and the central part of the Greater Caucasus are characterized by similarity in the elements of the deep structure and semithrust kinematics of interaction with the consolidated crust of the southern microplates–terranes framing the Arabian Plate from the north. The volcanoes of the Central Caucasus arose in a collisional setting and a relationship between Elbrus volcano and the Main Caucasian Thrust as a collision compression structure is assumed. Data were obtained on the results of geophysical studies using the earthquake converted-wave method (ECWM), microseismic sounding method (MSM), magnetotelluric sounding (MTS), and gravimagnetic measurements in combination with data obtained from processing of satellite images of the specific length of lineaments of tectonic fragmentation for different depths of lithospheric sections. Laboratory determination of radiocarbon dating of volcanic complexes, distribution of the thermal field in surface and deep thermal springs, as well as isotopic assessment of the ratios of indicator elements of Elbrus volcano, which make it possible to confidently identify a magma chamber at depth of ~5 km and a magma chamber at depth of ~30–40 km. Our studies allow us to consider the main characteristics as an increased thermal field, variations in the helium isotope ratios, a seismic gap under the volcanic structure, and insignificant energy unloadings occurring on gentle low-power tectonic zones on the northeastern and eastern slopes, where periodic fumarole gas emissions are inherent to the active volcano.