卷 51, 编号 3 (2017)

The paper describes the specific features of the bottom topography and morphostructural segmentation along the strike of the Southeast Indian Ridge (SEIR) and in the zones of influence of the Amsterdam–St. Paul hot spot and the anomalous zone of the relatively cold mantle in the area of the Australian–Antarctic discordance. Numerical estimates of changes of thermal state and strength of the crust in axial and off-axial zones of the SEIR were performed. Сorrelation between the thermal–rheological settings in the axial zone of the ridge with the seabed topography and the morphostructural segmentation and magmatism has been established. The numerical modelling results make it possible to assume the presence of along-axis asthenospheric flows under the axial zone of the SEIR. One of them, which was initiated by the Amsterdam–St. Paul point and the Kerguelen plume, is oriented from west to east, and the second, located east of the Australian–Antarctic discordance, is oriented from east to west. Taking into account the numerical modelling results of the thermal regime and the change in thickness of the brittle layer of the axial lithosphere, we performed a physical modelling of the influence of temperature anomalies in the mantle on the peculiarities of crustal deformation in the axial zones of the ridge. The experimental modelling showed that the presence of a thermal anomaly in the sublithosphere mantle in the form of a local heat source (hot spot) will noticeably influence the geometry of the rift axis and its position in relation to the hot spot. An area of anomalous topography forms under the influence of the hot spot, traces of which are preserved in the off-axis spreading flank zones, as in the case of the Amsterdam–St. Paul hot spot. More contrasting and dissected topography forms in zones with a relatively low typical mantle temperature in the process of crustal accretion.

In this work, we consider application of an original method for determining the indicators of the tectonic stress fields in the northern Baikit anteclise based on 3D seismic data for further reconstruction of the stress state parameters when analyzing structural maps of seismic horizons and corresponded faults. The stress state parameters are determined by the orientations of the main stress axes and shape of the stress ellipsoid. To calculate the stress state parameters from data on the spatial orientations of faults and slip vectors, we used the algorithms from quasiprimary stress computation methods and cataclastic analysis, implemented in the software products FaultKinWin and StressGeol, respectively. The results of this work show that kinematic characteristics of faults regularly change toward the top of succession and that the stress state parameters are characterized by different values of the Lode–Nadai coefficient. Faults are presented as strike-slip faults with normal or reverse component of displacement. Three stages of formation of the faults are revealed: (1) partial inversion of ancient normal faults, (2) the most intense stage with the predominance of thrust and strike-slip faults at north-northeast orientation of an axis of the main compression, and (3) strike-slip faults at the west-northwest orientation of an axis of the main compression. The second and third stages are pre-Vendian in age and correlate to tectonic events that took place during the evolution of the active southwestern margin of the Siberian Craton.

The increasing number of earthquakes in recent decades in Northwestern Iran and the determination of the epicenters of these events makes possible to estimate accurately the changing tectonic regime using the Win-Tensor inversion focal mechanism program. For this purpose focal mechanism data were collected from various sources, including the Centroid Moment Tensor catalog (CMT). The focal mechanism and fault slip data were analyzed to determine change in the stress field up to the present day. The results showed that two stages of brittle deformation occurred in the region. The first stage was related to Eocene compression in NE–SW direction, which created compressional structures with NW–SE strike, including the North and South Bozgush, south Ahar and Gushedagh thrust belts. The second brittle stage began in the Miocene with NW–SE compression and caused developing thrusts with N–S trends that were active presently. These stress regimes were created by the counter-clockwise rotation of the Azerbaijan plateau caused by movement on strike slip faults and continuous compression between the Arabian plate, the south Caspian basin and the Caucasus region. Pliocene-Quaternary activity of the Sabalan and Sahand volcanoes as well as recent earthquakes occurred as a result of this displacement and rotational movement. The abundance of hot springs in the Ardebil, Hero Abad and Bostanabad areas also bore witness to this activity.

In this paper we tried to identify the main tectonic lineaments in Eastern Iran including Lut block and Sistan suture zone from the airborne geomagnetic data together with tilt filter. As the map of obtained lineaments from airborne geomagnetic data has been studied, four distinct set of lineaments has been identified: (i) north–south, (ii) east–west, (iii) northeast–southwest, and (iv) northwest–southwest that are concurrently with structural zones and area’s big faults. New faults which have been identified in this investigation are lineaments with trend northeast–southwest and east–west. The depth of these lineaments has been calculated through Euler modeling. Magnetic lineaments trending east–west have the most depth, so these lineaments are related to basement faults.