Search

The specific features of the field of deep intrusions and tectonics of the NR are studied. It is shown that the formation of copper–nickel deposits in the study area in the Early Triassic is associated with the evolution of the stress field in the crust over 50‒100 Ma. It is established that the specific features of the formation of the intrusive field at the initial stage are associated with the deep and lateral heterogeneity of the stress state that arose before the onset of magmatism in the Early Permian in the crust of the Khantay‒Rybninsky uplift and adjacent structures. The emergence of this heterogeneity, which has an inherited long-term nature, is due to the formation of uplifts (swells) in the region and the processes of denudation of the surface of these uplifts (amplitudes of 1.5‒2.5 km). Since the processes of surface denudation lead to the release of rocks that have experienced a supercritical flow at great depths, in the upper part and, partially, in the middle part of the crystalline crust of the Khantay‒Rybninsky uplift and adjacent territories there were prerequisites for the emergence of a stress state of horizontal compression. In the lower part of the crust of the Khantay‒Rybninsky uplift, as well as in the crust of the Norilsk‒Kharaelakh trough and the Tunguska syneclise, the horizontal extension regime was preserved. This difference in the stress state of the crust determined the specific features of the spatial heterogeneity of the development of volcanism and intracrustal magmatism of the Norilsk‒Kharaelakh trough and Tunguska syneclise. [ABSTRACT FROM AUTHOR]

Shear fractures, dip-slip, strike-slip faults and their striations are preserved in the pre- and syn-rift rocks at Gulf of Suez and northwestern margin of the Red Sea. Fault-kinematic analysis and paleostress reconstruction show that the fault systems that control the Red Sea-Gulf of Suez rift structures develop in at least four tectonic stages. The first one is compressional stage and oriented NE-SW. The average stress regime index R' is 1.55 and S oriented NE-SW. This stage is responsible for reactivation of the N-S to NNE, ENE and WNW Precambrian fractures. The second stage is characterized by WNW dextral and NNW to N-S sinistral faults, and is related to NW-SE compressional stress regime. The third stage is belonging to NE-SW extensional regime. The S is oriented NW-SE parallel to the normal faults, and the average stress regime R' is equal 0.26. The NNE-SSW fourth tectonic stage is considered a counterclockwise rotation of the third stage in Pliocene-Pleistocene age. The first and second stages consider the initial stages of rifting, while the third and fourth represent the main stage of rifting. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]