COMPARISON OF MODERN GEODYNAMIC MODES OF FRAMING OF THE EUROASIAN LITHOSPHERIC PLATE

The purpose of the work is to analyze the modern geodynamic mode of framing of the Eurasian lithospheric plate to determine the types of deformations in the structures of spreading, subduction and rift genesis and favorable conditions for oil and gas formation at certain stages of structure development. The authors have analyzed the Arctic spreading zone, the Kamchatka subduction zone, the southwestern part of Eurasia and the Baikal rift system. The author's development of calculation of slip vectors of rock masses in foci of earthquakes and methods of tensor analysis of mechanics of fractured media were used in the work. Differences and similarities between the Arctic spreading zone, the Kamchatka subduction zone, the southwestern part of Eurasia and the Baikal rift system are shown. All of the above structures have a complex layered-block structure. That is, in a layered-block medium in layers, and in individual blocks and in time, the stress-strain state of the lithosphere changes, which directly depends on the direction of the axes of compressive stresses

The propagation velocity of seismic activity migrating along the directions of the geodynamic forces prevailing in the northeastern Baikal rift system, Russia

The recent tectonic stress field in the northeastern Baikal rift system (BRS) corresponds to the crustal deformation field. The stress-strain state of the Earth’s crust determines the fault network geometry and spatiotemporal structure of the epicentral field characterized by many earthquake swarms and earthquake migrations in the study area. In order to study the seismic process dynamics in different directions of the crustal deformation, the spatiotemporal analysis of earthquake time series has been made over the 1964–2015 instrumental period. To determine the relationship between crustal stress and spatiotemporal features of the epicentral field the seismic data were projected along horizontal stress tensor axes σ3 and σ2, consistent with major directions of the crustal deformation, a strike of major rifting structures, and a general azimuth of active fault groups. The NE-SW direction along the intermediate horizontal stress axes and main faulted arears exhibits slow earthquake migrations up to 60 km long, propagating with a modal velocity of about 30 kilometers per year. The NW-SE direction along the principal horizontal stress axes, orthogonal to the main faulted areas, is characterized by shorter migration sequences of less duration, propagating with a higher velocity than sequences registered in the NE-SW. The difference between the migration dynamics in mutually orthogonal directions can be attributed to the fault network configuration and the differences in the deformation process.

Volcanic rocks and pseudotachylytes from sources of crust-mantle complementary layers: Insight into geodynamics of the Baikal Rift System, Southern Siberia

<p>We present results of detail geochemical study of 18–12 Ma volcanic rocks from the Kamar-Stanovoy Zone of Hot Transtension (KSZHT), located in the central Baikal Rift System (BRS), and older pseudotachylytes from the Main Sayan Fault (MSF). These rocks designate geochemically distinguished from the OIB sources that are referred to the Slyudyanka zone of paleocollision occurred between the Khamardaban terrane and Siberian paleocontinent about 488 Ma ago. We define crustal and mantle signatures (with and without garnet, respectively) for the KSZHT volcanic rocks and crustal ones for the MSF basic pseudotachylytes. The signatures are indicative for tracing complementary relations between layers of the crust–mantle transition (CMT). We infer that the KSZHT volcanic activities accompanied rifting of a paleocontinental margin but got quiescent after a structural separation of the South Baikal Basin from the Tunka Valley, when the former had been sufficiently extended and subsided in contrast to the latter, which had been notably compressed and uplifted. From geological evidence and a detail seismic tomography model, we suggest that the KSZHT crust–mantle magmatic processes were due to delamination of a thickened root part of the South Baikal Orogen that preceded rifting in the South Baikal Basin area in the Late Cretaceous and Paleogene. Volcanic rocks of the past 17 Ma from the southwestern BRS denoted similar CMT sources and delamination processes beneath the East Hangay orogen and adjacent Orkhon-Selenga saddle. In the central and southwestern BRS, the CMT sources marked mutually overlapping deformational fields related to Indo-Asian convergence and pool-to-axis forces of the Japan-Baikal geodynamic corridor.</p><p>This work is supported by the RSF grant 18-77-10027.</p>