Geotectonics

Detailed lithological, stratigraphic, and structural studies of the fold-thrust structures were conducted on New Siberia Island. We have established that the jointly deformed complexes of the Upper Cretaceous–Middle Neopleistocene are overlapped by undeformed sediments of the Upper Neopleistocene. This fact confirms the completion of the deformation process at the end of the Middle Neopleistocene. An additional argument excluding the ancient age of dislocations is the result of the fission track dating for apatites. The resulting track ages of apatites significantly exceeded the age of deformed rocks, which was reliably established by the other methods. In deformed complexes, unlithified permafrost rocks predominate. Folded structures are characterized by joint deformation of sedimentary rocks, formation ice and ice-ground, inconsistency of fold orientation and different direction of structural evolution in the northern and southern parts of the island New Siberia. Considering the correspondence of the established age of dislocations to the age of the largest Pleistocene glaciation, all these facts allow us to state that the fold-and-thrust deformations of the island New Siberia are glaciodislocations.

The age and geodynamic position of the volcanic source of the Upper Jurassic–Lower Cretaceous deposits of Western Chukotka were determined. Products of synchronous volcanism were revealed by detailed lithological studies. Following sedimentological analysis results we established an admixture of pyroclastic material in the Oxfordian‒Kimmeridgian deposits of the Chukchi microcontinent, indicating the effect of synchronous volcanism on sedimentation. It was shown that the source of pyroclastic material was the intraoceanic Kulpolney island arc, which existed in the northern part of the Proto-Arctic Ocean.The accumulation of the Tithonian‒Valanginian deposits occurred in the back-arc basin at the edge of Chukotka microcontinent. Characteristics of the Tithonian‒Berriasian sandstones are given, which contain significant proportion of ash material in the matrix, as well as lithoclasts and monomineral grains of volcanic origin, predominant in the clasts. With the use of geochemical analysis of volcanic pebbles, the presence of the differentiated series from basaltic andesites to rhyolites in the volcanic source is proved. The suprasubduction origin of the volcanic source is established. The cessation of volcanic activity in Valangin era is confirmed by lack of presence of synchronous pyroclastic material and an insignificant amount of volcanic clasts in Valanginian sandstones. The obtained data of U‒Pb isotope dating of zircons isolated from the Tithonian‒Valanginian sandstones and andesite pebbles of the Tithonian conglomerates made it possible to determine the time for the existence of suprasubduction volcanism on the Chukotka margin in the period of 150‒140 Ma.

The Urf Al-Mahib area, located to the southern part of the Eastern Desert (SED) of Egypt, is covered mainly by juvenile Neoproterozoic crust and Nubian sandstones. Field investigation and structural analyses give evidence that the area of Urf Al-Mahib developed through four successive phases of deformation (D₁, D₂, D₃ and D₄). D₁ was an attenuated phase represented by tight to isoclinal folds (F₁), tightly appressed fold closures and sheared-out hinges, and axial plane foliation (S₁), as well as mineral and stretching lineations (L₁). Structural fabrics formed during the D₂ phase embrace minor- and map-scale prominent F₂ overturned folds with NW (to NNW)-dipping long upper limbs and short lower overturned limbs and axial planes striking NE (to ENE)‒SW (to WSW) and dipping to the NW at moderate angles. F₂ folds are geometrically- and kinematically-related to thrust propagation, and often have SE (to SSE) vergence. Thrust faults, that striking NE (to ENE)‒SW (to WSW) and dipping NW to NNW, are also common in this stage. D₃ structures contain pervasive vertical to inclined mesoscopic open to very open folds (F₃), whose axes plunge NW (to NNW) and SE (to SSE) at moderate to steep angles. The latest D₄ deformation phase is represented by abundant small- and large-scales WNW‒ESE trending dextral semi-ductile-semi-brittle-shear zones.

The Gulf of Aqaba is situated along the southern part of the Dead Sea Rift Area transform (DST), 1000 km (620 miles), the boundary between the African plate and the Arabian plate. It is situated toward the east of the Sinai landmass and west of Saudi Arabia. It is one of the joints interfacing the Asian and African landmasses. The Gulf expands 180 km from Eilat and Aqaba and joins the Red Sea in the Strait of Tiran, with the most extensive purpose of 28 km. On November 22, 1995, the biggest seismic tremor estimating 7.0 degrees happened along parts of the dead left line in the Gulf of Aqaba close to the port of Nuweiba in Egypt. This tremor made extraordinary harm Egypt and neighboring nations. Consequently, a few point by point investigations of seismology and geophysics have been led in the Gulf of Aqaba. In the territory researched, the vast majority of the ongoing seismic action revolved around the Gulf of Aqaba is portrayed by the contribution of moderate central quakes, an immediate aftereffect of the relative development between the plates of Africa, Sinai and the Arabian Peninsula. Seismic Energy along the Gulf of Aqaba locale is assessed utilizing a brief period (50 tests for every second) executed by the Egyptian National Seismic Network amid the period 1998‒2017. The connection between the dispatch and greatness of quakes in the Gulf of Aqaba demonstrated that the vast majority of the seismic Energy discharge originates from the biggest occasions and is packed in the inside, while it is moderately low in the southern and northern parts of the Gulf.

The Lower Oligocene Kal-e-kafi (East of Anarak, Central Iran) lamprophyres occur as stocks and dikes, which cross-cut the Eocene volcanic and Cretaceous sedimentary rocks. The predominant minerals of these lamprophyres are hornblende (magnesiohastingsite) and clinopyroxene (diopside) phenocrysts set in a fine- to medium-grained matrix of the same minerals plus plagioclase (labradorite to bytownite), sanidine, apatite, and magnetite. Secondary minerals are chlorite, magnetite, calcite, and epidote. Petrography, mineral chemistry, and whole rock compositions classify these rocks as calc-alkaline lamprophyre, in general, and spessartite in particular. These samples have intermediate compositions (SiO₂ ~ 58 wt %). The chondrite-normalized REE patterns and primitive mantle-normalized multi-element spider diagram of Kal-e-kafi lamprophyres are remarkably parallel and suggest that these dikes and stocks were derived from the same parental magma and underwent similar melt extraction. These rocks are enriched in alkalies, large-ion lithophile elements (e.g., Rb, Ba, K), and light rare-earth elements (e.g., La, Ce), and exhibit moderate to high fractionation in LREE patterns, with an average La/Lu ratio of 112. The large amount of hydrous fluids coming from the subducted slab rather than sediments caused to the enrichment and metasomatism of subcontinental lithospheric mantle source. Crustal contamination and assimilation of host rocks also played role in the genesis of these lamprophyres. Geochemical characteristics of the studied rocks suggest that parental magma have been derived from partial melting of a metasomatized amphibole-bearing spinel lherzolite of lithospheric mantle, which was previously modified by dehydration of a subducting slab. Subduction of oceanic crust around the Central-East Iranian Microcontinent (CEIM) is the most reasonable mechanism to explain enrichment in volatiles of the mantle, and the lamprophyric magmatism of the Kal-e-kafi area in Lower Oligocene times. Several tectonomagmatic discrimination diagrams indicate that the Kal-e-kafi lamprophyres occurred during postcollisional period of lithospheric extension.