A stratigraphic and structural study was carried out in the central part of the Chinese South Tianshan (STS) within a 50–100 km-wide transect centered on the Dushanzi-Kuqa road (83°–85° E). Our data elucidate the tectonic structure and evolution of the Palaeozoic sedimentary basin, document overthrust structures in the late Carboniferous-early Permian orogenic belt and suggest correlations between the western and eastern segments of the STS in Kyrgyzstan and China.We recognise a series of lithotectonic units in the study area that have different stratigraphic characteristics and were formed within (a) continental margin and slope of the Kazakhstan continent, (b) Turkestan (South Tianshan) ocean, (c) intra-oceanic carbonate sea-mounts, which at least partly evolved on top of an extinct island arc, (d) a back-arc oceanic-crust basin, (e) external deeper marine and internal shallow-marine areas of the Tarim shelf and (f) Tarim craton. The overall structure of the basin was similar within Kyrgyzstan and China. The main distinction of the western areas is a lack of ophiolites on the southern flank of the belt, a poorly expressed arc in the axial part, and a more complicated facial setting of the central area, where carbonate banks were separated by deeper marine depressions with cherty deposits. The eastern sector is defined by a continental arc that evolved on the northern margin of the Tarim craton in the Silurian and became separated from the continent in the latest Silurian-early Devonian. There is also a middle Palaeozoic metamorphic belt on the southern flank of the STS.A pre-Carboniferous unconformity, previously assumed throughout the study area, is only confirmed within the continental massifs of Kazakhstan and Tarim. As in the western areas, the unconformity does not exist within the STS. Continuous sedimentation in the STS occurred from the Early Devonian to the early Bashkirian in marginal parts of the belt and up to Gzhelian age in the axial part. Convergence began in the Bashkirian (320–315 Ma) and caused subduction of oceanic crust in the northern and southern areas of the STS to the north and south, respectively. A back arc basin in the south was closed in the Moscovian, and since that time top-to-the-south thrusting and overthrusting prevailed throughout the STS.The time of onset of collision of Kazakhstan with Tarim was not younger in age than Kasimovian, based on the age of initiation of a turbidite foreland basin on the northern margin of Tarim. Thrust deformation during the Late Pennsylvanian to early Permian was synchronous within Kyrgyzstan and China; it occurred in a collisional setting and was accompanied by accumulation of turbidites and olistostromes. Broad termination of thrusting, followed by folding and uplift of the area in the middle Asselian indicates the beginning of a rigid collisional phase. Emplacement of early Permian stitching granite plutons in the STS and adjacent areas of Kazakhstan and Tarim completes the formation of the collisional orogen within Kyrgyzstan and northwestern China.
Geological, petrologic, geochemical, and isotopic geochronological evidence for Grenville events at the western margin of the Siberian Craton are considered. These events were related to assembly of the Rodinia supercontinent. Multiple manifestations of riftogenic and within-plate magmatism at the final stage of orogenic evolution gave rise to breakdown of Rodinia and the formation of the Paleoasian ocean. The results allowed us to develop a new concept on the Precambrian geological evolution of the Yenisei Ridge and the processes that created its tectonic structure. The chronological sequence of events in the history of the Transangarian Yenisei Ridge is based on geological evidence and isotopic dating of Precambrian complexes variable in geodynamic nature. Four tectonic stages dated at 1.4−1.1, 1.1−0.9, 0.90−0.85, and 0.8−0.6 Ga were controlled by collision and extension recognized from large regional linear crustal structural elements. The evolution of the Transangarian Yenisei Ridge, which lasted for ∼650 Ma, corresponds in duration to supercontinental cycles that begin from rifting and breakdown of the predated supercontinent and was completed by orogeny and the formation of a new supercontinent. The regional geodynamic history correlates with the synchronous sequence and similar style of tectonothermal events at the periphery of the large Precambrian Laurentia and Baltica cratons. This is evidenced by paleocontinental reconstructions, which confirm close spatiotemporal links of Siberia with cratons in the northern Atlantic 1400−600 Ma ago and indicate incorporation of the Siberian Craton into the ancient Nuna and Rodinia supercontinents.
The paper deals with issues related to the study questions on magmatic tectonics and intragranitic hydrocarbon accumulating formation: (i) post-magmatic structure of granitic massifs containing hydrocarbons; (ii) mechanisms of structure-material processing, exhumation and forming porosity in granitic bodies on post-magmatic evolutional stage; (iii) availability and distribution of hydrocarbon deposits in granitic massifs located in different geodynamic settings and different regions; (iv) description of crystal piercing bodies ‒ granite protrusions. The role of structural tectonic factor in intra-granitic hydrocarbon accumulating was estimated. An evolutionary structural-tectonic model of their formation within granitic massifs and, above all, granitic protrusions is proposed.
Diagenesis is a necessary process for the development and formation of clastic reservoirs and ultimately determines the reservoir physical property. The evolution of pores is the comprehensive outcome of compaction, cementation, and dissolution in the process of burial history, and diagenetic material and diagenetic field control the type of diagenesis and its intensity. This systematic procedure and the coupling relationship among them are discussed using geology prediction technique to simulate the evolution of the diagenetic stages, diagenetic facies, and porosity of clastic reservoirs and ultimately for favorable reservoir prediction, particularly a reservoir of low porosity and low permeability. The essence of this method is illustrated using Ed1 clastic sandstones in the Bozhong depression. Core data shows that the diagenetic stages of Ed1 lake sandstones is classified into early diagenetic stage B, middle diagenetic stage A1.The major diagenetic processes that influence the porosity of the sandstones in study area are mechanical compaction (Com), carbonate cementation (C-Car), quartz cementation (C-Qua), clay cementation (C-Clay), feldspar dissolution (D-Fel), and carbonate dissolution (D-Car). Quantitative analysis of porosity evolution show that pore change rates in per million years caused by Com, C-Car, C-Qua, C-Clay, D-Fel, D-Car are 1~3, 0~2, 0~3, 1, 0~4, and 0~1%, respectively, in different diagenetic stages. C-Car is mainly in early diagenetic stage A and early diagenetic stage B, while D-Car is in middle diagenetic stage A1. D-Fel is mainly in early diagenetic stage B and middle diagenetic stage A1. Diagenesis including Com, C-Clay, and C-Qua is all well developed in these stages. Finally, based on single well simulation, diagenesis model and diagenesis strength model are summarized to simulate the porosity of the study area.
A structural-facies map of the Bashkir stage of the Caspian basin, the southeastern part of the East European platform and the Turan plate is compiled on the basis of drilling data generalization. The sequence of tectonic events and sedimentation processes in the early‒ late Bashkir century of the middle Carboniferous was reconstructed. It is shown that cessation of reef formation, appearance of erosion surfaces and partial destruction of the side ledges of Caspian depression occurred under the influence of Varis orogenesis and the global fall of the World Ocean level due to the glaciation of the Paleogondvana at the turn of early‒middle Carboniferous. It is assumed that oil and gas reservoirs in the rocks of Vise‒Bashkir age are confined to large bodies of carbonate-clastic rocks with clinoform structure that arose on the slopes of the depression due to destruction of its side ledges.
Modeling of the most common types formation of anticlinal and uplift-thrust tectonic structures was carried out with using optical polarization and tectonic-sedimentary methods based on seismic sections analysis of various areas and deposits located in the West Siberian oil and gas basin that were selected for examples. Experiments with using the optical-polarization method allowed us to research the nature of the stress-regime arising in the gelatin models of the sedimentary cover due to the growth of anticlinal blocks and uplift-thrust dislocations. By the level of tangential stresses and orientation of isoclines in optical models, zones of probable tectonogenic fracture and the direction of cracks are predicted. 2D tectonic-sedimentation modeling made possible to explain the mechanism of formation of “rootless” uplifts, zones of subsidence or decompression in sediments, the principle of tectonic “pump” function, and to obtain dependencies between size and shape of uplift, density and opening of cracks formed above, to calculate the value of fracture “porosity”, as well as lateral dimensions of zones of tectonogenic fracturing. 3D tectono-sedimentation modeling allowed to link hydrography of the earth surface of the simulated area with decompression of zones that came to the surface in the models. These zones of decompression can serve as a search sign for exploration of highly productive zones containing hydrocarbon deposits.
We present a new technique for shear wave splitting analysis in anisotropic mantle by combining the splitting analysis of Ps phases in receiver functions and SKS splitting analysis. Ps converted phases reveal evident variations in the effective arrival time as a function of back-azimuth in the anisotropic layer. This variation can be used to stacking to obtain the fast polarization direction and split time for an anisotropic layer. Our method was applied to data collected from the Iranian broadband permanent stations. Using teleseismic data, from 2004 to 2008, with magnitudes greater than 5.5 recorded at 14 permanent stations, we attempted to study crustal anisotropy beneath the stations. Then, we combined our results of the crustal anisotropy obtained from the receiver function analysis with the results of the SKS analysis to discrimination of crust and mantle deformation. The fast directions were parallel to the suture zone in the mantle beneath lower boundary of Central Iran micro-plate. The fast direction was almost parallel to the Alborz Mountain zone and perpendicular to the Zagros orogenic belt. Assuming that the fast polarization direction in the mantle is parallel to mantle flow, our investigation reveals the occurrence of horizontal melt flow which causes movement of the Arabic plate towards the Central Iran micro-plate.
Global experience in oil exploration and the discovery of the Tupi field in Brazil and the Tiber field in the Gulf of Mexico in the last decade have confirmed the existence of giant oil fields with abnormally high formation pressures at depths of 10 km or greater. Until recently, the discovery of large oil accumulations in deeply buried reservoirs was considered as theoretically impossible. This work suggests that giant oil accumulations at great depths (6–10 km) should be considered important hydrocarbon exploration targets in the Russian Federation and the Eurasian Union. The first-priority oil and gas exploration targets at great depths are deeply buried horizons of the sedimentary cover of the Precaspian basin, whose subsalt hydraulic system is characterized by ubiquitous abnormally high formation pressures. The deeply buried reservoirs in the Astrakhan oil and gas accumulation zone are considered the most promising for the discovery of giant oil accumulations. Data discussed below demonstrate that hydrocarbon exploration and the discovery of giant oil accumulations at great depths require specific exploration procedures and techniques.
The article discusses the ratio of the size and spatial position of ancient and modern areas of geodynamic processes (tectonic-sedimentary systems) and the resulting geological bodies. It has been established that regardless of the rank and geodynamic affiliation of tectonic-sedimentary systems at all levels, from local to supra-regional, the implementation of geological processes proceeds along the path of least energy expenditure. In the modern structure of the Atlantic-Arctic Rift System, this trend is expressed in the development of strike-slips on the principle of maximum straightening of transfer zones between its segments. In the future, it will also determine progradation of the rift system through Eurasian platform region.
Through several stations on the forelimb of the Es Satah anticline belonging to Gafsa basin part of the southern Tunisian Atlas, an analysis of the striations encountered on the pebbles surfaces in the conglomerates of the growth-strata shows a remarkable variation; vertically and laterally from one station to another. Taking into account of the simple shear deformation, field observations have revealed several indexes of the flexural flow. Both of the tectonic and micro-tectonic studies in the Gafsa basin have shown the trending shortening (σ1) ranging from 150° to 180° N. Therefore, the striation azimuths were determined according to three profiles, I, II and III. These profile stretch from the NE to the SW on the forelimb of Es Satah anticline which displays a variation ranging from 167° to 138° N, from 165° to 147° N and from 154° to 138° N, respectively. Since these variations are incoherent with the regional shortening (σ1) direction, it allows us to discard any evidence of a direct relationship between the regional trending shortening (σ1) and the striation azimuths of the pebbles surfaces of growth-strata and to speculate a possible direct correlation between those variations and the kinematic evolution of the Es Satah anticline. Accordingly, we have suggested a conceptual model which paved the way to follow step by step the anterior stages of the deformation and identify the different palaeo-periclinal limits of the Es Satah anticline.
A structural-facies map of the Bashkir stage of the Caspian basin, the southeastern part of the East European platform and the Turan plate is compiled on the basis of drilling data generalization. The sequence of tectonic events and sedimentation processes in the earlya late Bashkir century of the middle Carboniferous was reconstructed. It is shown that cessation of reef formation, appearance of erosion surfaces and partial destruction of the side ledges of Caspian depression occurred under the influence of Varis orogenesis and the global fall of the World Ocean level due to the glaciation of the Paleogondvana at the turn of earlyamiddle Carboniferous. It is assumed that oil and gas reservoirs in the rocks of ViseaBashkir age are confined to large bodies of carbonate-clastic rocks with clinoform structure that arose on the slopes of the depression due to destruction of its side ledges.
In our paper we produce new evidence of the tectonosphere and hydrosphere structure of oil and gas sedimentary basins and confirm significant influence of geofluid-dynamic processes on formation of hydrocarbon accumulations in the crust at the great depths. In our opinion the theory based on obsolete views on the tectonosphere structure lessen the importance the sedimentary migration theory of hydrocarbon generation. We prognosticate a particular stagnant type of post-elysionic water-drive systems in the crust at the great depths in conditions of increased hydrodynamic isolation. Absence of regionally sustained vertical and lateral drainage layers characterizes geological environment where stagnant type developed, and, corollary, fluids outflow into external environment is practically unfeasible. The subsalt filling complexes of the epicontinental deepwater basins are included into the post-elysionic water-drive systems. These complexes occur at the great depths and possibility of striking unique and large oil and gas fields there is inherent. We propose a system of fluid-dynamic conditions for preserving hydrocarbon accumulations in the lower crust as a result of developing sedimentary-migration theory for oil and gas formation. We consider the refinement of methods for prospecting and exploration large deposits at the great depths will pave the way for expanded reproduction of hydrocarbon reserves in the “old” oil and gas producing regions in our country.
There are three stages in tectonic evolution of the Earth: (1) nucleation, from the origin of protocratons to their assembly into the Kenorland supercontinent (2.7–2.5 Ga); (2) cratonization, from the breakup of Kenorland (2.45 Ga) to the assembly of Columbia (1.85 Ga) and its reorganization into Rodinia (1.0–0.72 Ga); and (3) modern plate tectonics, from the breakup of Rodinia 720 Ma until the present. Analysis of the time-space reorganizations of Archean granulite–gneiss terranes, which correspond to continental lithospheric keels, reveals five groups of protocratons (Nena, Ur, Congo–Sahara, NAsia and Atlantica) that remained almost intact during long time intervals. After the breakup of Kenorland, the continental crust rotated counterclockwise. NAsia and Atlantica rotated the least and drifted relative to Nena; however, the latter rotated by 180○. Congo‒Sahara, Ur, and Kalahari rotated the most. The assembly and breakup of the supercontinents clearly correlates with secular changes in dominant types of base, precious, and ferrous metal deposits, as well as the formation and emplacement of diamonds.
Lake Nasser is situated in an area with a very non-recurring earthquake, and revealed the history of Egypt registered 5000 years ago. After seventeen years of filling the Aswan High Dam reservoir began a long series of earthquakes caused. The main shock, Ms. = 5.6, occurred on November 14, 1981, preceded by several factions, followed by a large number of aftershocks. Thirty-three years later, seismic activity remains, but is much lower in frequency and volume. The aim of this paper is to study the effect of the reservoir on the induced seismic and determine the coordination mechanism of some earthquakes that occurred in the northwestern part of High Dam reservoir. These investigations indicate that seismic activity occurred mainly along the Kalabsha fault and small parallel sectors, and there is a range of activities in the Khor al-Ramla area, about 40 km southwest of the High Dam. From 1982 to the end of 2017, seventy-five earthquakes with a magnitude of 3.5 ≤ M < 4.0 and 13 earthquakes of magnitude greater than or equal to 4.0 have occurred. It also shows that these earthquakes occurred during loading and unloading periods. This shows that the effect of the reservoir itself does not produce earthquakes, and there is no direct relationship between changing the daily rate and the magnitude of earthquakes. So it can’t be used as a predictor in the case of the Aswan reservoir, which is a unique reservoir in its behavior. The focused coordination mechanism of four different seismic zones in the west of Lake Nasser shows errors in striking the strike with a simple natural element. The P (pressure) and T (tension) stress axes are trending ESE–WNW and NNE–SSW, respectively.
Crustal-scale extensions occurred in the Tibetan Plateau during the post-collision stage, and leucogranites, N–S and E–W faults and other tectonic-thermal events were developed in Tethys Himalaya, which formed a series of Pb–Zn–Sb–Au polymetallic deposits. The ore deposit may be distributed around the dome (with core of leucogranites), or along the N–S and E–W faults. Due to the lack of deep geophysical data, many different genesises of mineral deposit have been proposed by predecessors. This paper establishes the spatial relationship of deep tectonic-thermal events in the Tethys Himalaya Pb–Zn–Sb–Au belt by the N–S magnetotelluric (MT) profiles covering Cuonadong dome, the Southern Tibet Detachment System (STDS) and other tectonic-thermal events (length: 72 km, the basic point distance: 1 km): (a) a partial melting body was observed about 15 km below the Tethys Himalayan, which intruded in the form of leucogranites and formed domes; (b) the STDS and its secondary faults extended to deep the partial melting body. In combination of time relationship of tectonic-thermal events, a view has been presents that the Tethys Himalaya Pb–Zn–Sb–Au belt was formed in one tectonic‒thermal coupling metallogenic system in the post-collision stage. Two types of metallogenic models were formed based on whether the partial melting intruded or not: (a) the tectonic‒thermal coupling metallogenic model of leucogranites and the surrounding detachment faults of the dome (partial melting intruded in the form of leucogranites which driven ore-forming fluid to migrate in the surrounding detachment faults); (b) the tectonic‒thermal coupling metallogenic model of non-intruded partial melting and fault systems (under the extension stress, the N–S extension of Tibetan Plateau had formed the STDS and its secondary fault faults that extended to the partial melting body). This results in instantaneous low pressure, which decoupled the partial melting body and magmatic fluid and drove magmatic fluid and deep formation fluid to flow into fault system. Finally, the two fluids were mixed with atmospheric water to form ore. Also a hydrodinamical model for the long distance migration of ore-forming fluid along the fault systems within the Tethys Himalaya Pb–Zn–Sb–Au belt has been established. This study will provide a reference for subsequent geophysical prospecting in the belt.
The Earth’s lithosphere is commonly investigated by both direct and indirect methods, corresponding to rock sampling and geophysical surveys, respectively. The interpretation of geophysical data is generally based on the combination of values measured in the lithosphere with those obtained in laboratories from rock samples. However, petrophysical properties of numerous lithotypes overlap, yielding the misleading interpretation of geophysical surveys in many areas of the world. A heated debate particularly concerns non-volcanic rifted margins, fuelled by the possible presence of giant oil and gas fields: thinned continental crust or serpentinized oceanic basement. One of the possible causes of ambiguity is related to the intimate similarity of oceanic serpentinites and various crustal rocks (e.g. basalts, gabbros, limestones, sandstones, shales, etc.), in terms of petrophysical properties. Can variably serpentinized peridotites mimic typical continental crustal rocks, such as granites and granodiorites? To answer this question, we compared literature data of worldwide samples of such lithologies. The results show the complete overlap of the considered petrophysical properties (density, magnetic susceptibility, V P, V S, V P/V S, and Poisson’s ratio) of these lithotypes (P = 10–1000 MPa, depth = 0.33–33.33 km), further confirming the difficulty in discriminating variably serpentinized mantle rocks from crustal lithologies. Therefore, the recognition of buried serpentinite geobodies, being potential sites of exploitable gas and oil reservoirs, like those probably ensconced in non-volcanic rifted margins, necessitates a robust lithological model inferred from direct methods, namely the study of core drillings, deep-seated xenoliths and tectonic exposures of deep-crustal sections to substantiate the interpretation of geophysical data.
The formation of an island-arc back-arc slope is considered based on the of the Upper Cambrian‒Middle Ordovician arc in the Chingiz Range in eastern Kazakhstan. The study demonstrates its occurrence during waning volcanic activity in the island-arc structure, from the end of the early Arenig (end of the Floian Age of the Early Ordovician) with the appearance of tephroturbidites. After the cessation of volcanism, two sedimentation cycles were distinguished in the slope’s sedimentary sequence in the Middle Ordovician: (1) transgressive when the island arc submerged (2) and regressive when the Chingiz arc began to build up at the beginning of the Llanvirn (Darriwilian). Sedimentation was repeatedly accompanied by landslide processes, which ended in the middle of the Llanvirn (Darriwilian) with breakup of the tectonic-gravity plate composed of Upper Cambrian volcanic rocks with limestone in the sole, caused coarsely fragmented mixtite to form in front of the allochthonous mass and the further sedimentation on the back-arc slope to stop.
The study has analyzed the distribution of noble metals, rare metals, and rare earth elements in Paleocene and Lower–Middle Miocene coals of the Zeya–Bureya sedimentary basin. The basin’s formation in the Mesozoic and Cenozoic has been reconstructed by detailed paleogeographical analysis of Cenozoic coal-bearing sequences based on the geodynamic features of the development of adjacent regions. Geological events at the turn of the Cretaceous and Paleogene have been considered. The metal content in the basin’s frame has been comprehensively analyzed. It has been demonstrated that the conditions for the migration and localization of trace elements occurred mainly due to the geodynamics that developed on the northwestern flank of the Zeya–Bureya basin, including static orogens in the Paleocene–Miocene, where sedimentation was actively expanding. Trace element migration, which encompassed denudation plains, occurred in stable processes of peat accumulation and localization of economically important components in waterflows associated with the plains. Contrasting conjugate forms in the flexure–uplift system and uneven localization of trace elements were controlled by the high level of geodynamic activity on the southeastern margin of Zeya–Bureya sedimentary basin. The presence of gold has been identified throughout the strata of Paleocene and Lower–Middle Miocene coal-bearing sediments in the Sergeevka, Yerkovtsy, and Raychikhinsk deposits. Coals of the Sergeevka deposit are enriched in Be, Sc, V, Ga, Rb, Nb, Ta, and REE + Y.
Crustal-scale extensions occurred in the Tibetan Plateau during the post-collision stage, and leucogranites, N-S and E-W faults and other tectonic-thermal events were developed in Tethys Himalaya, which formed a series of Pb-Zn-Sb-Au polymetallic deposits. The ore deposit may be distributed around the dome (with core of leucogranites), or along the N-S and E-W faults. Due to the lack of deep geophysical data, many different genesises of mineral deposit have been proposed by predecessors. This paper establishes the spatial relationship of deep tectonic-thermal events in the Tethys Himalaya Pb-Zn-Sb-Au belt by the N-S magnetotelluric (MT) profiles covering Cuonadong dome, the Southern Tibet Detachment System (STDS) and other tectonic-thermal events (length: 72 km, the basic point distance: 1 km): (a) a partial melting body was observed about 15 km below the Tethys Himalayan, which intruded in the form of leucogranites and formed domes; (b) the STDS and its secondary faults extended to deep the partial melting body. In combination of time relationship of tectonic-thermal events, a view has been presents that the Tethys Himalaya Pb-Zn-Sb-Au belt was formed in one tectonicthermal coupling metallogenic system in the post-collision stage. Two types of metallogenic models were formed based on whether the partial melting intruded or not: (a) the tectonicthermal coupling metallogenic model of leucogranites and the surrounding detachment faults of the dome (partial melting intruded in the form of leucogranites which driven ore-forming fluid to migrate in the surrounding detachment faults); (b) the tectonicthermal coupling metallogenic model of non-intruded partial melting and fault systems (under the extension stress, the N-S extension of Tibetan Plateau had formed the STDS and its secondary fault faults that extended to the partial melting body). This results in instantaneous low pressure, which decoupled the partial melting body and magmatic fluid and drove magmatic fluid and deep formation fluid to flow into fault system. Finally, the two fluids were mixed with atmospheric water to form ore. Also a hydrodinamical model for the long distance migration of ore-forming fluid along the fault systems within the Tethys Himalaya Pb-Zn-Sb-Au belt has been established. This study will provide a reference for subsequent geophysical prospecting in the belt.
Geometric and seismic parameters of the Qoshadagh Fault (QDF) were investigated to evaluate seismic hazard along this fault, which consists of three segments. The central E–W striking, dextral-reverse segment is the longest and terminates at both ends into NW–SE striking splay arrays. Both eastern and western splay arrays form locally transtensional bends. Paleoseismic data obtained from three excavated trenches across the fault combined with dated offset geomorphic features revealed that the central segment experienced at least 5 surface rupturing earthquakes during the past 2.5 ka, with maximum moment magnitude of Mw = 6.8 ± 0.2. The mean recurrence interval for the identified paleoearthquakes is 452 ± 143 years (±2σ) and the calculated amount of slip per event is ca. ≈0.85 m. These results imply that the QDF slips at an average rate of 1.9 ± 0.1 mm yr–1 for over the past 2.5 ka. The obtained values define the seismic behavior of the fault and are essential to remediate ensuing seismic risks.