Basis Of Tectonics Research Articles

Использование вероятностно-статистических методов для анализа формирования генерационного потенциала глубокопогруженных отложений Верхнепечорской впадины

The Upper Pechora Basin is located in the north of the Pre-Ural foredeep. The structure of the upper horizons of the sedimentary cover is well studied, but there is a poor information about deeply buried sediments confined to the eastern side of the depression. Therefore, modeling of the formation of oil and gas potential of great depths is of interest. In this paper, the problem is solved by applying probabilistic and statistical methods. The values of the total generation potential, the concentration of organic carbon, the rate of burial, the depth and the thickness of the layers were used for the analysis. In addition, since the Upper Pechora Basin is characterized by a sharply asymmetric structure, it was divided into two tectonic zones: the western (outer slope) and the eastern (inner slope). As a result, fundamental differences have been established in the conditions of generation potential formation for the studied types of organic matter and tectonic zones. Comparison of the average values of generation potential and the factors influencing its formation showed the presence of statistical differences between the types of kerogen in the deeply buried sediments of the Upper Pechora Basin, as well as between tectonic zones. Correlation analysis has determined that both positive and negative relationships with varying degrees of closeness are observed between the studied indicators. Using linear discriminant analysis, it was determined that sapropel and humus organic matter are separated quite clearly, and the mixed type practically does not stand out according to the specified characteristics, it was also revealed that the separation occurs on a tectonic basis. A step-by-step regression analysis for each of the parameters under consideration, carried out for these types of kerogen separately, confirmed a significant difference in the accumulation processes of sapropel and humus types of kerogen, as well as the western and outer sides of the depression. Thus, the conducted probabilistic and statistical analysis showed the regulatory role of tectonic factors in the processes of generation potential formation.

Seismotectonics of Armenia: main problems

The article describes the main problems in the existing researches on the seismotectonics of the territory of Armenia. A review was conducted on certain issues related to the accuracy of the initial seismological data, the problem of identifying possible focal zones of strong earthquakes, and the probabilistic assessment of the seismic hazard of the territory of Armenia. As the results of numerous studies show, the initial seismological data from catalogs and bulletins are characterized by their heterogeneity. Different observation systems and different methods of seismological data processing have led to the fact that when visualizing the spatial distribution of earthquake epicenters on the territory of Armenia, during the instrumental period of observations, an artificially lattice network of epicenters is obtained, which does not agree in any way with the fault tectonics of the territory. During the stud of distribution of earthquake hypocenters by depth, the discrete nature of their distribution was revealed. There is also a number of disadvantages in the area of allocation of focal zones of strong earthquakes. The main part of the conducted research was mainly based on data on previously recorded strong seismic events, as well as on data on historical earthquakes, as a result, for the most part of the studied territory, in fact, no research was conducted. In addition, there are relevant questions about the tectonic basis used in these studies. The last group of problems concerns the probabilistic assessment of the seismic hazard of the territory of Armenia. It is shown that in the existing works, there are quite a lot of unsubstantiated assumptions.Based on the analysis, it is concluded that in the field of seismotectonic studies of the territory of Armenia, there are a number of urgent tasks that require priority solutions.

Formation conditions of the Rudny Altai metallogenic province

The results of previous geological, petrochemical, and metallogenic surveys conducted from the 1960s to the 1990s provide the geological and tectonic basis of this study. The unique mineral deposits of the Rudny Altai metallogenic province were formed in the Middle Paleozoic (S2–C1) at the junction between different structures of the Altai–Mongolian terrane: the Alei–Charysh–Tigirek rift (in the north) with the Korgon–Markakol’ island arc and Belaya Uba–Maimyr intra-arc trough (in the southwest). The Rudny Altai structural–formational zone that formed at the junction between these structures evolved as a magmatic arc and was characterized by the formation of granite–greenschist arches, volcanoplutonic magmatism and high heat and fluid flow (greenschist-facies metamorphism of Upper Silurian–Upper Devonian rocks and deposition of pyrite-bearing hydrothermal–sedimentary horizons, VMS and copper–VMS deposits and isolated base-metal ore bodies). The tectonomagmatic history of the Rudny Altai zone can be subdivided into several stages: Ludlow–Emsian, Late Emsian–Givetian, Frasnian–Early Famennian, Middle Famennian–Early Visean, and Late Visean–Serpukhovian. The island arc is represented by volcanic rocks of the andesite–dacite–rhyolite (early stage), basalt–rhyolite (Late Emsian–Eifelian), and basalt–andesite–rhyolite series (Late Visean). Volcanosedimentary strata (until the Givetian age) and turbidites up to 3–5 km thick were deposited in the interarc trough. Because of their metastable behavior, the volcanic rocks became actively involved in ion-exchange reactions with the formational waters, whereas the differences in hydraulic head between arches and troughs created favorable conditions for the transport of the metamorphic fluids, and the thermal gradient promoted thermodiffusion of divalent species of Mg, Pb, Zn, Cu, etc. toward the high-temperature zone and development of the high-Mg metamorphic–metasomatic alteration with a VMS–base-metal mineralization. As a result, ore deposits of different structural and genetic types were formed. Temperatures of ore formation (200–400°C) were controlled by thermal effect of pyrite dissolution and replacement reactions. The ore composition and regional metallogenic zoning were defined based on their position with respect to interarc and interarch troughs and the chemistry of the metal-extraction environment.

Probability in PSHA: Reply to "Comment on 'PSHA Validated by Quasi-Observational Means' by Z. Wang"

One of the attractions of the Monte Carlo simulation approach to seismic hazard is its conceptual simplicity and directness. What a site operator wants to know is what type of earthquake shaking his plant might possibly have to endure in its lifetime. In response, the seismologist takes all the available information on regional seismogenesis, distils it into a numerical model, and then uses that model to investigate all the possible earthquake ground motions that might occur at the site. Given a sufficient number of simulations, every possible outcome will be sampled, and the most likely outcomes will be observed more often than the less likely outcomes. Wang (2012), in commenting on the description of this method in Musson (2012a), states that randomization of an earthquake catalog is an insufficient approach to assessing seismic hazard, as it ignores the tectonic basis for seismicity, and cannot include possible future events not represented in the historical catalog, such as the 2011 Tohoku event. Such a catalog randomization approach has been suggested in the past, for instance by Ebel and Kafka (1999). But this is not what is described in Musson (2012a). Simulated catalogs used for hazard analysis are not randomizations of the historical catalog, but realizations of possible future events based on what is known about regional seismicity. Any individual simulation may have a different number of events from the historical catalog, but it will be consistent with what is known about local seismotectonics. So it may include larger earthquakes than those observed historically, up to a limit inferred from the tectonic situation. Indeed, a catalog randomization approach would not be able to reproduce Cornell-type results as shown in Musson (2012a), since the model used as an example in that paper includes a fault which is assessed on the basis that …

Continuous GPS and broad-scale deformation across the Rhine Graben and the Alps

In order to study the ongoing tectonic deformation in the Rhine Graben area, we reconstruct the local crustal velocity and the strain rate field from GPS array solutions. Following the aim of this work, we compile the velocities of permanent GPS stations belonging to various networks (EUREF, AGNES, REGAL and RGP) in central western Europe. Moreover, the strain rate field is displayed in terms of principal axes and values, while the normal and the shear components of the strain tensor are calculated perpendicular and parallel to the strike of major faults. The results are compared with the fault plane solutions of earthquakes, which have occurred in this area. A broad-scale kinematic deformation model across the Rhine Graben is provided on the basis of tectonics and velocity results of the GPS permanent stations. The area of study is divided into four rigid blocks, between which there might be relative motions. The velocity and the strain rate fields are reconstructed along their borders, by estimating a uniform rotation for each block. The tectonic behaviour is well represented by the four-block model in the Rhine Graben area, while a more detailed model will be needed for a better reconstruction of the strain field in the Alpine region.

CHEMICAL COMPOSITION OF SANDSTONES

The author has collected 168 chemical analyses from the literature. All analyses with less than 5 per cent Al 2 O 3 (“quartzite” clan) were removed. The remaining analyses were divided on a tectonic basis into three clans; taphrogeosynclinal, eugeosynclinal, and others (mainly exogeosynclinal). Histograms for the seven major oxides and variation diagrams for K 2 O/Na 2 O and alkalies/Al 2 O 3 indicate that the tectonic associations group together clans of chemical analyses which differ significantly from each other. The eugeosynclinal graywackes especially differ from other sandstones by their low K 2 O/Na 2 O ratio, which is correlated with the presence of basic volcanic detritus. Arithmetic and geometric means for the seven major oxides for the four clans are as follows (given to two significant figures):