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This article presents an interpretation of geophysical data that characterizes the structure of the piedmont folded zone of the Urals and Pay-Khoi, which shows the diversity of structural styles of deformations in the study region. The following structural styles of deformations are considered: classical thrust zones, which are imbricated overlapping of thrust plates (i); areas of development of wedge-shaped allochthons, composed of duplex tectonic plates that do not have direct expression in the overburden strata (ii); inversion zones where faults are associated with the Ural rifting are transformed into thrust faults (iii); areas whose structure is determined by the deformation of salt diapirs and extrusion of salt (iv); zones of tectonic thickening of the Precambrian complexes overlain by the Paleozoic cover (v). Interpretation of historical and new data on the structure of fold belts makes it possible to significantly update our understanding of the structure and development of areas such as zones of wedge-shaped thrusts, areas of development of squeezed salt diapirs, and areas where reactivation and tectonic thickening of Precambrian complexes occurred due to the reactivation of pre-existing faults. The new seismic data provide constraints on the magnitude of horizontal displacements in the thrust zones as well as timing of phases of deformation. For the first time they have revealed the development of zones of low-amplitude proto-thrusts. [ABSTRACT FROM AUTHOR]

The article presents a brief overview of the currently existing ideas about the seismotectonic situation in the Earth's crust of Iran, which is experiencing intense compression in the northeastern direction as a result of collision of the Arabian and Eurasian lithospheric plates. The survey also involved geodetic data in the form of modern GPS measurements of horizontal surface displacements. The stress-strain state of the Earth's crust of Iran (construction of the average focal mechanism) was assessed based on data on the total set of 945 focal mechanisms of earthquakes of average strength (4.4 ≤ MW ≤ 6.5) according to the ISC catalog, which occurred from 1975 to 2020, within 12 spatial samplings. The focal mechanisms of the strongest earthquakes in the last 50 years (MW = 6.0–7.4) for one event in each of these samplings are also considered. The calculated parameters of the average mechanisms and focal mechanisms of strong earthquakes are compared both with each other and with the surrounding tectonic situation and the distribution of deformation velocity vectors according to GPS observations. A satisfactory correspondence has been established between all the comparable values. The differences in the type of formation of the seismogenic layer of the Earth's crust of Iran in different regions are demonstrated. These differences are manifested in different ratios of shear and thrust components in the reconstructed mean mechanism in different spatial samplings. A similar difference is noted in individual focal mechanisms of the strongest earthquakes. However, it is possible to describe the observed nature of deformation of the crust of Iran within a single concept of collisional tectonics, caused by collision of the Arabian and Eurasian plates in the last 5 Ma. [ABSTRACT FROM AUTHOR]

In northeastern Algeria, the Souk Ahras foreland basin is a part of the Maghrebides fold-thrust belt and comprises Sellaoua and Medjerda High units in the footwall of Tellian thrust sheets. Detailed geological mapping supported by micro-paleontological, petrographic, and structural data allows us to reappraise its stratigraphy and its structural style and to characterize the relationship between the different structural units (Numidian, Tellian, Sellaoua, and Medjerda High units). Data were collected for a biostratigraphy and field observations along to six (06) sections spread over the Ouled Driss, Dj. Boubakhouch, Dj. Boukebch – Dekma, and the Medjerda High. The Souk Ahras foreland basin substrate is made up by Jurassic and early Cretaceous series and constituted an outer shelf pre-foreland passive margin where salt tectonics occurred. From upper Cretaceous to Miocene, flexural subsidence and thrust wedge propagation took place as the result of the northward drift of Africa plate. The Souk Ahras foreland is finally deformed by thrust-related folds, which affected a pre shortening tectonic pile involving remnant of salt tectonics influenced margin during at least Cretaceous times. [ABSTRACT FROM AUTHOR]

The eastern Sichuan-western Hunan and Hubei belt (ESWHHB) is an important fold-thrust belt in the Middle-Upper Yangtze region of China, and it is also an important area for petroleum and gas prospect in China. The influence of mechanical stratigraphy on the deformation evolution of the ESWHHB is a hot problem that has received widespread attention. However, due to the complexity of geological conditions, this issue has not been sufficiently addressed. Previews geological exploration studies show that the deformation evolution of the belt is closely related to the mechanical stratigraphy. Physical simulation has proven to be effective for studying the deformation evolution of fold-and-thrust belt. Based on the geological conditions of the ESWHHB, six groups of physical models were designed to analyze the influences of the ductile layer and overlap configuration on the structural deformation of the ESWHHB. The results show that the mechanical stratigraphy has significant control on the deformation evolution of the fold-thrust belt. The ESWHHB evolution is related to the lower viscosity of the ductile layer and the larger thickness of the ductile layer, while only gradual propagated fold-and-thrust belt can be resulted from the higher viscosity of the ductile layer and the smaller thickness of the ductile layer. Additionally, the overlap between the stratigraphy at various structural belts leads to significant differences in their mechanical properties, and it critically influences the structural patterns of the ESWHHB. [ABSTRACT FROM AUTHOR]

The Rocky Mountain Foothills lie along the eastern margin of the Rocky Mountain fold-thrust belt. The area has been the focus of extensive research aimed at locating oil and gas fields with the potential to be used as CO storage traps. In this study, we use a seismic line from the Canadian Rockies to interpret the geologic structures along a cross-section parallel to the tectonic transport direction. We then compare our results with those of previous studies. The section was restored using the MOVE software (manufactured by Midland Valley Exploration Ltd.). The primary objectives of this work are: (1) to conduct a stratigraphic and structural interpretation of a 2D seismic profile; and (2) to conduct a cross-sectional restoration of the structures in order to validate the seismic interpretation in terms of CO storage candidates. Additional data sources include maps of the surface geology, which show that the age of horizons decrease from west to east, and stratigraphic and structural profiles derived from well logs. The results of our structural restoration indicate a detachment fault between the foreland and hinterland. This fault is responsible for the cutting and subsequent upwards and eastwards movement of a stratum located between the basement and the Late Devonian formation. Large thrust faults are responsible for the deformation of strata (through both folding and faulting) in the foreland basin. As a result of continuous eastward tectonic stress, the strata from Jurassic have deformed, forming a duplex system in the middle of the section and resulting in the uplift of the upper part of the section. Following surface erosion, this uplifted area became exposed during the Tertiary Period. The high shortening rate (53%) detected through structural restoration is consistent with the thin-skinned tectonic model. [ABSTRACT FROM AUTHOR]

Apatite fission-track dating and thermal-history modeling were carried out on samples from the Dabashan (大巴山), a fold-thrust belt, northeast of the Sichuan (四川) Basin and east of the Tibetan Plateau. A first cooling event in the Late Cretaceous is followed by a prolonged period of thermal stability with exhumation rates of ≤0.025 mm/a, as determined from age vs. elevation relationships. The preservation of age vs. elevations relationships and the lack of distinct age changes across tectonic structures indicate that the Dabashan fold-thrust belt formed prior to the Late Cretaceous, consistent with the current view of Triassic-Early Cretaceous shortening. Relatively short mean track lengths (∼12 μm) indicate that the samples remained in the partial annealing zone for a prolonged time. The knick points in the best-fitting temperature-time models suggest that the onset of late-stage accelerated cooling commenced at ≤11 Ma. Related exhumation rates are 0.3-0.2 mm/a assuming geothermal gradients of 20 and 30 °C/km. We speculate that this late-stage event results from eastward growth of the Tibetan Plateau and overstepping of the Sichuan Basin, it is likely responsible for the youthful morphology of the Dabashan. [ABSTRACT FROM AUTHOR]

Thrust duplexes account for large fractions of the total shortening in most fold-thrust belts (FTBs). They also provide an efficient mechanism for transferring slip upward from the basal decollement and for transporting roof thrust sheets over long distances. The Lesser Himalayan duplex (LHD) plays a prominent role in the overall evolution of the Himalayan FTB and has been described from Garhwal-Kumaon to Bhutan. In Sikkim the LHD shows unique structural geometry and has been responsible for transporting crystalline thrust sheets (MCT 1 and MCT 2) farther southward than other parts of the Himalaya. Such lateral variations in LHD geometry imply variations in the kinematic history of the Lesser Himalaya and variations in shortening and shortening history along the length of the Himalayan arc, and these are reflected in observable large scale structural patterns. [ABSTRACT FROM AUTHOR]