Geotectonics最新文献

Abstract

Orthopyroxene granitoids (designated as charnockites or granitoids of the charnockite series) are characterized by varying silica and felsic mineral content, with the orthopyroxene (hypersthene) phase as the main characteristic mafic mineral component. These rocks are abyssal and represent parts of intrusions or form their own igneous complexes at the depth of the lower crust under CO₂-undersaturated and dry conditions, which can be achieved within any tectonic setting. Therefore, petrogenetic models for orthopyroxene granitoids as well as for all types of granitoids from different locations are sufficiently applicable for a reconstruction of paleogeodynamic conditions in a certain region. The East Antarctic shield is characterized by Archean blocks embedded within orogens of Mesoproterozoic, Late Mesoproterozoic‒Early Neoproterosoic and Late Neoproterosoic‒Early Paleozoic age, and syn- and post-orogenic intrusions composed of orthopyroxene granitoids and related rocks are widely spread and form a prominent volume of the East Antarctic orogens. According to paleogeodynamic reconstructions of Rodinia, Pannotia and Gondwana supercontinents the East Antarctic shield represents a significant volume of supercontinents’ crust. Petrogenetic models for East Antarctic orthopyroxene granitoids became fundamental for any paleogeodynamic reconstractions of supercontinents. We collected structural geology, tectonics, and geochronology data for orthopyroxene granitoid intrusions belonging to orogens of certain age and combined with the plotting of geochemical data in major and rare element tectonic discrimination diagrams, also analyzed the Sm‒Nd isotope system data. The East Antarctic orthopyroxene granitoids tightly related to orogens are characterized by magmatic sources determined as combination of mafic lower crust, upper crust and juvenile mantle materials mixing up in different proportions depending on type of orogeny. It was established that orthopyroxene granitoids related to Mesoproterozoic and Late Mesoproterozoic‒Early Neoproterosoic orogens formed at different stages of long-lived collision transforming from ocean‒continent to continent‒continent types whereas Late Neoproterosoic‒Early Paleozoic orthopyroxene granitoids arose in post-collision tectonic setting.

Abstract—

The results of ²³⁰Th/U dating of massive sulfides and metalliferous sediments (288 and 245 analyses, respectively) of hydrothermal sites in the northern equatorial area of the Mid-Atlantic Ridge (MAR) from 12° to 20° N are presented. The maximum and average ages of sulfides are 223 ± 38.2 and 80.5 ka, respectively. The comparison of ages of massive sulfides from various MAR hydrothermal sites showed asynchronous stages of hydrothermal activity along the ridge axis indicating the features of tectonic activity and magmatism, which control the hydrothermal activity within each region. The glaciation periods, which record the activation and low- and high-temperature hydrothermal activity, are an exception. A direct positive correlation between the age of a hydrothermal site and its distance from the axial ridge zone is typical of mafic-related hydrothermal sites in contrast to ultramafic-related hydrothermal sites, which is related to the different scenarios of the formation of these two types of sulfide mineralization within slow-spreading ridges. The ages of sulfides and sediments have been jointly analyzed based on the example of the Pobeda and Semenov hydrothermal sites. The interpretation of data on sediments indicates the continuous character of hydrothermal activity, which is partly supported by the age of sulfides.

Abstract

The Gramberg All-Russia Research Institute for Geology and Mineral Resources of the World Ocean (FSBI VNIIOkeangeologia) carries out a wide range of research in the fields of geology, engineering geology, geophysics, and geochemistry. The specialists of the institute perform studies using most-up-to-date equipment in several directions, including the study of the geology and mineral resources of the Arctic, Antarctic and the World Ocean. The geological and tectonic maps and atlases of the Eurasian sector of the Arctic shelf and adjacent deepwater zones of the Arctic Ocean have been compiled. This allow one to recognize the rift-related basins on the East Arctic shelf of Russia, and the conjunction areas of the Lomonosov, Gakkel, and Mendeleev oceanic ridges with the Eurasian continental margin. A comprehensive interpretation of geological and geophysical data has revealed features of the tectonics of the Amerasian Basin, which indicate that the evolution of the basin structures took place under conditions of continental rifting. One of the main scientific conclusions drawn at the preparation of the Submission of the Russian Federation in respect of the continental shelf boundary in the Arctic Ocean is the proof of the continental nature of the structures of the Central Arctic Rise Complex: the Lomonosov Ridge, Podvodnikov Basin, Alpha–Mendeleev Rise, Chukchi Basin, and Chukchi Borderland. This conclusion is confirmed by the characteristics of the main layers of the Earth’s crust in the above structures. A geodynamic model of the evolution of the Precambrian complexes of East Antarctica has been developed and the main tectonic provinces of Antarctica have been distinguished. A universal seismostratigraphic model of sedimentary basins has been developed for the marginal seas of East Antarctica. An important area of research in Antarctica was the study of the subglacial Lake Vostok. When studying the history of the formation of sulfide mineralization, it was found that the discharge of hydrothermal ore-bearing solutions most often occurs continuously, and only the intensity of the ore formation process changes with time. The possibility of formation of massive sulfide ore volumes additional to the main surface deposit due to metasomatic replacement of host igneous rocks has also been established.

Abstract

The article presents the results of studying and substantiating the age of the Ediacaran volcanogenic-sedimentary and Cambrian sedimentary strata isolated for the first time within the southern part of the Ulutau terrane (southern Ulutau) in the west of Central Kazakhstan. The age estimates (SHRIMP II) of 594 ± 3, 594 ± 5, and 600 ± 2 Ma obtained for effusive and tufogenic rocks, as well as their isotope-geochemical characteristics, are the first evidence of the manifestation of Ediacaran suprasubduction magmatism in the paleozoics of Kazakhstan and the northern Tien Shan. The obtained data indicate the participation of the Ulutau terrane at the end of the Precambrian in the structure of the volcanic-plutonic belt, fragments of which are also Neoproterozoic blocks within southwestern Kazakhstan (the Zheltavsky and Chuysko-Kendyktassky terranes) of the Southern Tien Shan and the Karakum‒Tajik terrane. The formation of the Ediacaran suprasubduction belt may be a continuation of the evolution of the Neoproterozoic active continental margin that arose in the Tonian period on the northwestern margin of the supercontinent Rodinia.

Abstract

The Puchezh–Katunki crater is located in the central part of the East European Platform in the area of the Gorky Reservoir, has a diameter of ~80 km, and is morphologically expressed by the central uplift of the basement (Vorotilov knoll) and the ring depression surrounding it, on the periphery of which there is a ring terrace. The crater is filled with various coptogenic (explosive (?)) formations: breccias of various types and bodies of suevites and tagamites. The results of studying the U‒Th‒Pb isotope system of detrital zircon grains from variegated explosive Puchezh breccias in the northwestern part of the ring terrace (three samples) are presented. The weighted average of the three youngest U‒Pb dates of detrital zircons from all studied samples is 258 ± 7 Ma, which corresponds to the Late Permian. We take this date as the lower age limit of the Puchezh breccias. The age sets of detrital zircon grains from the studied samples and from (1) crystalline rocks of the Vorotilov knoll and suevites of the ring depression and (2) Upper Permian–Lower Triassic sandstones of the Zhukov Ravine reference section (Moscow Syneclise) were compared. The absence of zircon grains, whose U‒Th‒Pb isotope system is similar to the parameters of those from the rocks of the Vorotilov knoll and suevites among the detrital zircons from the Puchezh breccia indicates the local nature of the Puchezh–Katunki explosion, the impact-thermal impact of which did not affect the detrital zircons in rocks of the marginal part of the ring terrace of the crater. A high degree of similarity of the age sets of detrital zircon grains from the lens of redeposited sandstones of the Puchezh breccias and Upper Permian rocks of the Zhukov Ravine section indicates that the Puchezh breccias were formed mainly due to the reworking of the Upper Permian–Lower Triassic sequences underlying the explosive formations. We consider the Uralian paleo-orogenic belt as the main provenance area for the deposits of the central regions of the East European Platform in the stratigraphic interval close to the Permian–Triassic boundary. The deposits were formed as a result of a high degree of mixing and averaging of clastic material of sedimentary flows containing the Uralian and Asha provenance signals.

Abstract

New data on the geological position, U‒Pb SIMS zircon ages, petrogeochemical features, Sr‒Nd isotopic composition, and geodynamic setting of the granitoids and volcanics of the Northern volcanic-plutonic belt of the Verkhoyan–Kolyma fold area are presented. Magmatic rocks of the belt include granitoids of Elikchan, Kuranakh, and Bakyn plutons, composed of Elikchan granite–granodiorite complex and volcanics of predominantly intermediate-felsic Tumusskaya sequence with subvolcanic bodies of the same composition. They form a single Early Cretaceous (127–121 Ma) volcanic-plutonic assemblage. Granitoid plutons are elongated in a sublatitudinal and northwestern direction and are discordant to main fold-and-thrust structures. Granitoids intrude and metamorphose Jurassic terrigenous and Early Cretaceous volcanics of Tumusskaya sequence and are intruded by younger Late Cretaceous subvolcanic bodies. Granitoids of Bakyn, Elikchan, and Kuranakh plutons combine petrogeochemical features of I-, S-, and A-type granites. Such diversity of petrogeochemical granitoid types, as well as interrelations of major (({text{F}}{{{text{e}}}_{{text{2}}}}{text{O}}_{3}^{{{text{tot}}}})–TiO₂–MgO) and rare (Ba/La–Nb × 5–Yb × 10) elements in granitoids and the same age volcanics of the Tumusskaya sequence, allow us to refer them to igneous rocks of transform or sliding plate boundaries. Collision between the Chukotka microcontinent and the Siberian continent with the earlier accreted Kolyma–Omolon microcontinent in Barremian–Aptian time changed to postcollisional extension and formation of volcanic-plutonic assemblage of the Northern volcanic-plutonic belt. Postcollisional extension took place at the transform or sliding plate boundaries. Sr–Nd isotopic characteristics of granitoids of all granite plutons indicate the interrelation of mantle and crustal sources of granitoid melts in this process.

An Erratum to this paper has been published: https://doi.org/10.1134/S0016852123140017

Abstract

Barite mineralization is visible as veins in the Kuik‒Qureq area, southern part of Sanandaj zone, Western Iran. Geological and structural maps of the area were prepared using remote sensing data and field achievements. Statistical analysis of fractures included the ratio of distance and length to abundance, and also the calculation of the fractal dimension of fractures. This analysis indicates the role of structural controls on the barite mineralization in the region. Petro-fabrics were used to determine displacement and contribution of faults in barite mineralization. Geometric analysis using rose diagrams determined that the trends of the dominant fractures are N‒S and NN‒S, NNW‒SSE, WNW‒ESE and NNE‒SSW, and the main barite mineralization was formed along these faults. A tectonic model is presented for the region based on classifying fractures by azimuth and features observed in thin section. According to the proposed model, at least four stages of tectonic deformation affected the region and during these the direction of the σ₁ axis changed in a clockwise direction. Barite mineralization mainly occurred in two stages: the first and main stage when first order fractures formed with the N‒S trend, and during the third deformation stage when secondary barite was deposited in third order fractures with an E‒W trend.

Abstract

Fars sub-basin is located in the Zagros fold-thrust belt and includes a large number of hydrocarbon reserves, especially gas. The existence of numerous basement faults and strike-slip in this region along with the uplift and depocenter of basement blocks has been considered effective factors in controlling sedimentary basins before, after, and synchronous with sedimentation. In this study, the role of the Razak fault basin in the external Fars area as an effective factor in controlling the sedimentary basin was evaluated. For this purpose, by providing isopach maps and 3D modeling from the basin floor at synsedimentary formations, the activity of the Razak fault along with its role in increasing or decreasing the hydrocarbon potential of the region and adjacent anticlines, was investigated. The results show that the inactivity of this fault at the sedimentation time of the Dalan, Gadvan, Darian, and Kazhdumi formations, while at the deposition time, the formations of Kangan, Dashtak, Hith, Fahlian, Laffan, Ilam, and Pabadeh remained active and controlled the sedimentation in the basin. Also, the uplift and depocenter of the basement blocks occurred to the Razak fault’s performance, caused an increase in the hydrocarbon potential of the Dehram Group in the anticlines of Marz, Varavi, Tabnak, Dehnow, Khalfani, Chiru, and Madar. While the northeastern part of the study area and the anticlines of Bonashkatu, Pishvar, Bavush, Gavbast, and Gezzeh are less important. In addition, Khami and Bangestan reservoirs are also without hydrocarbon potential due to the Razak fault’s performance.