Journal articles: 'Zone of collapse and densified rocks' – Grafiati (2024)

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Phenomenon of surrounding rock deformation and collapse, groundwater lowering, ground collapse and cracking appeared in a tunnel project. It is necessary to study mechanical properties of alteration zone for guarantying construction safety and ensuring the reliability of supporting structures. This paper, using geological survey and microanalysis methods, determines the mineral composition of all typical altered rocks in the alteration zone. Furthermore, an overall understanding of their physical and mechanical characteristics will be presented based on the results of physical and mechanical (triaxial and direct shear tests) tests.

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A laterally extensive, Neoproterozoic extensional detachment (the Betsileo shear zone) is recognized in central Madagascar separating the Itremo sheet (consisting of Palaeoproterozoic to Mesoproterozoic sediments and underlying basem*nt rocks) from the Antananarivo block (Archaean/Palaeoproterozoic crust re-metamorphosed in the Neoproterozoic). Non-coaxial deformation gradually increases to a maximum at a lithological contrast between the granitoids and gneisses of the footwall and the metasedimentary rocks of the hangingwall. Ultramylonites at this highest-strained zone show mineral-elongation lineations that plunge to the southwest.σ-, δ- and C/S-type fabrics imply top-to-the-southwest extensional shear sense. Contrasting metamorphic grades are found either side of the shear zone. In the north, where this contrast is greatest, amphibolite-grade footwall rocks are juxtaposed with lower-greenschist-grade hangingwall rocks. The metamorphic grade in the hangingwall increases to the south, suggesting that a crustal section is preserved.The Betsileo shear zone facilitated crustal-scale extensional collapse of the East African Orogeny, and thus represents a previously poorly recognized structural phase in the story of Gondwanan amalgamation. Granitic magmatism and granulite/amphibolite-grade metamorphism in the footwall are all associated with formation of the Betsileo shear zone, making recognition of this detachment important in any attempt to understand the tectonic evolution of central Gondwana.

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Purpose. To increase the stability of the wellbore during its construction in unstable rocks. Methodology. To solve the set tasks, an integrated approach is used in the work, which includes critical analysis and generalization of scientific and technical achievements in combination with theoretical and experimental research. Findings. Factors influencing the stability of the borehole walls in conditions prone to rock slides and rock falls are analyzed. Expediency of using baths for strengthening the walls of wells in deposits of clay rocks, including clay shales, has been established and substantiated. A formulation of a fuel-bituminous bath has been proposed, the installation of which in a well for 78 hours makes it possible to increase the initial compressive strength of rocks, which will ensure the integrity of the borehole walls. It is recommended to use corrugated casing pipes to cover the sections of the wellbore where there is intensive crumbling and collapse of rocks. Originality. For the first time, the main factors of wall destruction have been established and a method has been developed to prevent the destruction of walls of directional wells composed of rocks prone to loss of stability under the action of drill string loads. Practical value. To combat the collapse of the walls of the well composed of rocks, prone to loss of stability, the authors suggested setting up fuel-bituminous baths in the range of complications. In case when the collapse of the walls of the well can not be prevented with a fuel-bitumen bath, it is proposed to overlap the area of collapse with the casing using advanced corrugated casing pipes with the injection of adhesive into the rock mass in the near-wellbore zone. The use of an adhesive material increases the contact area of the metal shell with the rock, which collapses increasing the stability of the borehole walls.

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AbstractLatest Devonian A-type granite-gabbro plutons, in part ductilely deformed, are spatially associated with the strike-slip Cobequid fault zone. The youngest intrusions are close to the Cobequid fault zone, which was the main conduit for magma. Two phases of deformation accompanying magma emplacement are recognized. Early magmas intruded ductile rocks during left-lateral oblique thrust movements. A second stage of right-lateral oblique slip normal faulting accommodated uplift of the plutons when coarse granite was emplaced in the crestal regions. Cross-cutting late stage porphyries, granitic clasts in marginal basins cut by granitic dykes, and superposition of brittle on ductile structures all indicate rapid uplift of the plutons. The geometry of the Cobequid fault zone shows that pluton emplacement was not the result of extension in releasing bends during transcurrent shear. Rather, flower-structure high-angle faults acted as magma conduits and space was created by two processes: translation of wall rocks along thrust faults at depth, developing space away from the master fault zone and backward collapse of the uplifted magma chamber creating space towards the fault zone.

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A metamorphic core complex of latest Oligocene age crops out in the Kazdağ mountain range in northwest Turkey. The footwall of the core complex consists of gneiss, amphibolite and marble metamorphosed at 5 ± 1 kbar and 640° ± 50 °C. The average muscovite and biotite Rb/Sr ages from the gneisses are 19 Ma and 22 Ma, respectively, and imply high temperature metamorphism during latest Oligocene times. The hangingwall is made up of an unmetamorphosed Lower Tertiary oceanic accretionary melange with Upper Cretaceous eclogite lenses. The hangingwall and footwall are separated by an extensional ductile shear zone, two kilometres thick. Mylonites and underlying high-grade metamorphic rocks show a N-trending mineral lineation with the structural fabrics indicating down-dip, top-to-the-north shear sense. The shear zone, the accretionary melange and the high-grade metamorphic rocks are cut by an undeformed granitoid with a 21 Ma Rb/Sr biotite age, analytically indistinguishable from the Rb/Sr biotite ages in the surrounding footwall gneisses. The estimated pressure of the metamorphism, and that of the granitoid emplacement, indicate that the high-grade metamorphic rocks were rapidly exhumed at ∼ 24 Ma from a depth of ∼ 14 km to ∼ 7 km by activity along the shear zone. The subsequent exhumation of the metamorphic rocks to the surface occurred during Pliocene–Quaternary times in a transpressive ridge between two overstepping fault segments of the North Anatolian Fault zone. The high-grade metamorphic rocks of the Kazdağ range are surrounded by voluminous calc-alkaline volcanic and plutonic rocks of Late Oligocene–Early Miocene age, which formed above the northward-dipping Hellenic subduction zone. The magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest Turkey prior to the onset of extension suggest that the latest Oligocene regional extension was primarily related to the roll-back of the subduction zone rather than to the gravitational collapse.

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Gas-dynamic danger of Krasnoslobodsky fracture zone in Starobin Deposit of potassium salts was investigated. The study was carried out taking into account the existing ideas about the mechanism of formation of foci of gas-dynamic phenomena in the salt rock mass of the field, as well as taking into account the results of seismic and hydrogeological studies of the fault zone and the revealed patterns of distribution of gas-dynamic phenomena over the field area. The features of the geological structure of Krasnoslobodsky fracture zone in the upper salt stratum containing layers of potash ore are established. The features of the mechanism of evolution of hydrodynamic systems in fault zones are revealed. It was found that the functional system of halogen metasomatosis in these zones of the rock mass was not shielded, so that the absorption zone of the hydrodynamic system was located in the rocks of the clay-marl strata located above the upper salt strata and horizons of possible mining operations, and fractured rocks of the fault zone provided gas filtration from the system of voids formed during the evolution of hydrodynamic systems. According to the results of the study, it was concluded that in Krasnoslobodsky fracture zone within the upper salt layer there were no conditions for the formation of dangerous foci of gas-dynamic phenomena, such as sudden emissions of salt and gas and collapse of roof rocks. Accordingly, there is a possibility of safe mining operations, such as the penetration of intersecting workings through the fault zone.

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Silicocarbonate pegmatites from the southern Grenville Province have provided exceptionally large crystal specimens for more than a century. Their mineral parageneses include euhedral calc–silicate minerals such as amphibole, clinopyroxene, and scapolite within a calcite matrix. Crystals can reach a meter or more in long dimension. Minor and locally abundant phases reflect local bedrock compositions and include albite, apatite, perthitic microcline, phlogopite, zircon, tourmaline, titanite, danburite, uraninite, sulfides, and many other minerals. Across the Adirondack Region, individual exposures are of limited aerial extent (<10,000 m2), crosscut metasedimentary rocks, especially calc–silicate gneisses and marbles, are undeformed and are spatially and temporally associated with granitic pegmatites. Zircon U–Pb results include both Shawinigan (circa 1165 Ma) and Ottawan (circa 1050 Ma) intrusion ages, separated by the Carthage-Colton shear zone. Those of Shawinigan age (Lowlands) correspond with the timing of voluminous A-type granitic magmatism, whereas Ottawan ages (Highlands) are temporally related to orogenic collapse, voluminous leucogranite and granitic pegmatite intrusion, iron and garnet ore development, and pervasive localized hydrothermal alteration. Inherited zircon, where present, reflects the broad range of igneous and detrital ages of surrounding rocks. Carbon and oxygen isotopic ratios from calcite plot within a restricted field away from igneous carbonatite values to those of typical sedimentary carbonates and local marbles. Collectively, these exposures represent a continuum between vein-dyke and skarn occurrences involving the anatexis of metasedimentary country rocks. Those of Ottawan age can be tied to movement and fluid flow along structures accommodating orogenic collapse, particularly the Carthage-Colton shear zone.

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This paper is dedicated to research into the geological peculiarities, shape of the ore body and the occurrence of the host rocks in the hanging wall of the Pivdenno-Biloz- erske deposit , as well as their influence on the degrees and quality of high-grade iron ore extraction. It is noted that in the interval of 480 – 840 m depths, a decrease is observed in the stability of the natural and technogenic massif, which is caused by the increase in rock pressure with depth, the influence of blast- ing operations on the massif and the difference in geological conditions. This has led to the collapse of hanging wall rocks and backfill into the mined-out space of chambers in certain areas of the deposit, the dilution of the ore and deterioration of the operational state of the underground mine workings. Attention is focused on the causes and peculiarities of consequences of the collapse of the hanging wall rocks during ore mining, which reduce the technical and-economic indexes of the ore extraction from the chambers. A 3D-model of an ore deposit with complex structural framework has been developed, which makes it possible to visually observe in axonometric projection the geological peculiarities and the shape of the ore body. The parameters have been studied of mining chambers in the 640 – 740 m floor under different changing geological conditions of the ore deposit and hanging wall rocks occurrence – the northern, central and southern parts. The difference in the iron content in the mined ore relative to the initial iron content in the massif has been defined as an indicative criterion of the influence of changing conditions on the production quality. The reasons have been revealed which contribute to the collapse of the rocks and the subsequent decrease in the iron content of the mined ore in ore deposit areas dif- fering by their characteristics. It has been determined that within the central and half of the southern ore deposit parts with a length of 600 m, an anomalous geological zone is formed, the manifestation of which will be increased with the depth of mining. It was noted that within this zone, with the highest intensity and density of collapse of hanging wall rocks, the influence of decrease in the slope angle and change in the strike direction are of greatest priority, and such geological factors as a decrease in hardness, rock morphology, deposit thickness increase this influence significantly. To solve the problems of the hanging wall rocks’ stability, it is recommended to study the nature and direction of action of gravity forces on the stope chambers in the northern, central and southern parts, as well to search for scientific solutions in regard to changes in the geometric shapes of stope chambers and their spatial location, improving the order of reserves mining in terms of the ore deposit area, the rational order of breaking-out ore reserves in the chambers with changing mining and geological conditions of the fields’ development.

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To achieve the objective with the claimed technical result, a method of fastening mine workings of predominantly rectangular cross-sectional shape with anchor bolts was used, while the applied task of reducing the heaving of soil rocks is to increase the efficiency of mine workings by ensuring that the mine workings. Ensuring the possibility of reliable and of good quality fortified rocks along the contour of making within the boundaries of the zone of possible collapse of rocks. The length of the soil anchors did not significantly affect the condition of the soil rocks. Consequently, that on the deformations and stresses both in the lateral and in the soils are not soil, but lateral anchors. The use of these technological developments will reduce the cost of conducting and maintaining workings by 7–10% with soil anchors (reducing maintenance costs by 7–10%) and will provide an economic effect of 10–15 thousand tenge per running meter of output.

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A brief analysis of the prevention of sand blockage in wells is considered. One of the most common complications during the operation of wells in Azerbaijani oil fields is sand formation. During sand formation, wells are stopped for a while, their repair takes a long time, and as a result, significant well product losses occur. The sand that comes with the fluid entering the wellbore destroys the equipment and at the same time forms a blockage in the wellbore. The removal of the sand plug requires heavy labor, but sometimes leads to oil losses in many wells and leads to the collapse of rocks in the wellbore zone and the deformation of the production pipeline. The collapse of the bedrock and the prevention of sand congestion are still one of the most pressing issues in the oil industry. Despite numerous scientific studies and mining experiments on the mechanism of sand formation prevention, no universal method has been found to combat sand formation. The collapse of the bedrock and the prevention of sand congestion are still one of the most pressing issues in the oil industry. Keywords: sand plug, well, sand plug removal, well bottom filter, surface filter, well bottom zone

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AbstractBorehole log data gathered during a subsidence investigation in 1978–79 are used to derive a classification scheme for Coal Measure rocks. The results of height of void migration above workings are compared to those arising from use of Piggott & Eynon’s (1977) geometrical collapse zone method and Bienawski’s (1980) Rock Mass Rating scheme. It is concluded that the analysis helps to assess areas of greatest instability, which thus aids land-use planning and also the planning of ground investigations, ground stabilization, and re-development.

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Archean rocks in the Fenton Lake – Brown Lake area, southern Slave Province, are subdivided into two lithotectonic domains: a supracrustal domain, which consists mainly of the Archean Yellowknife Supergroup, and a gneiss–granite domain. The latter is composed of gneissic and metaigneous rocks of the Sleepy Dragon Complex, determined to be basem*nt to the Yellowknife Supergroup, and granite plutons, including the 2641 ± 3.5 Ma Suse Lake granite and the 2583.5 ± 1 Ma Morose Granite. Volcanic rocks of the Cameron River Belt and greywacke–mudstone turbiditic metasedimentary rocks of the Burwash Formation constitute the supracrustal domain.A late Archean, amphibolite- to greenschist-facies, ductile to local brittle, high-strain zone separates the domains. Kinematic indicators demonstrate that the zone experienced two kinematically opposed episodes of displacement. The older episode involved pre- to synthermal peak thrusting of the supracrustal rocks over the gneiss–granite domain. Thrusting is kinematically and temporally consistent with late Archean, pre- to synthermal peak, regional contractional deformation. Structural and metamorphic relations and kinematic indicators suggest that thrusting and regional contraction were followed shortly by intrusion of the peraluminous Morose Granite and thereafter by a late syn- to post-thermal peak episode of extension, resulting in tectonic unroofing of the gneiss–granite domain.The sequential history of contraction and attendant regional metamorphism, granite intrusion, and, ultimately, extensional collapse, which is documented in the Archean rocks in the area, is a common feature of Phanerozoic collisional orogens. Moreover, the tectonic history of the gneiss–granite domain is broadly similar to the evolution of metamorphic core complexes in the North American Cordillera.

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The distribution of REE in groundwater of the catchments, which were formed during the long-term operation of copper mines in the Middle Urals (Russia), was studied. The groundwater composition reflects a significant removal of REE from water-bearing rocks, which leads to their enrichment by several orders of magnitude relative to the oceans, surface water and groundwater. Maximum REE values (up to 15 mg/L) were recorded in groundwater discharged to the surface in the collapse zone (pH=3.5). In mine shafts REE values do not exceed 0.3 mg/L. Water of mine wastes occupy an intermediate position: here REE content varies from 0.5 to 6.5 mg/L. The degree of REE fractionation in mine waters is lower than in oceanic, surface and underground waters of the active water exchange zone at much higher contents. The chemical composition of groundwater of the abandoned copper mine is determined by hypogene processes and structure of the mineralized supergene zone, its mineralogical composition, and oxidation-reduction conditions.

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AbstractMost unroofing mechanisms invoked for the exhumation of blueschist-plus-eclogite terranes, including corner-flow and extensional collapse of the orogenic wedge, predict steep unroofing paths for the deeply-buried rocks and are applicable only to unroofing from depths within the crust. Many high-P and ultrahigh-P rocks of continental affinity are derived from greater depths than this. Their lack of warming during unroofing, together with indications that they may rest directly on less deeply buried equivalents, are suggestive of shallow unroofing paths similar to those for the subduction-channel model. They are interpreted to have been emplaced by the upward extrusion of coherent slices of continental crust, bounded below by thrust faults and above by normal faults, with unroofing paths essentially reversing the original burial paths.Where continental crust has been subducted into the mantle, upward extrusion is probably driven largely by buoyancy forces, although examples of upward extrusion without subduction into the mantle indicate that buoyancy forces may not be essential. Two features in addition to buoyancy may promote upward extrusion. Slab breakoff may reduce the pull from the descending slab, and subduction-zone geometry may change as a continental margin is dragged into the subduction zone. Both features may promote the extrusion of continental crust at precisely the time at which it has been partially subducted.A close spatial relationship between a lateral ramp and a lobate zone of extruded high-P rocks in the Mesoproterozoic Grenvillian orogen indicates that lateral ramps may be important in localizing extrusion. Lateral ramps disturb the two-dimensional flow, with channelling of material into the region of the lateral ramp as it is extruded. Many exhumed ultrahigh-P terrains are associated with jogs in the trends of orogenic fronts that may reflect the presence of lateral ramps at depth. Ultrahigh-P rocks may be expected to be concentrated at such jogs, and may record the channelling in their deformation history.

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Structural, metamorphic, and U–Pb geochronological data bear on the distinction between Archean and Paleoproterozoic tectonism along the southeastern margin of the Rae Province on Baffin Island. Archean rocks include ca. 3.0–2.8 Ga gneiss, two greenstone belts of the Mary River Group, and various younger granitoid intrusions. In the greenstone belts, intermediate–felsic volcanism (2.74–2.725 Ga) was accompanied and outlasted by calc-alkaline plutonism (2.73–2.715 Ga). Deformation, low- to medium-pressure metamorphism, and peraluminous plutonism followed at ca. 2.7 Ga. Archean rocks and the locally overlying Piling Group (ca. 2.2–1.9 Ga) were deformed and metamorphosed together during development of the Paleoproterozoic Foxe fold belt. Tectonism is linked to the Isortoq fault zone, a major southeast-dipping structure marking an abrupt northwestward transition to granulite facies. Within a 5-km-wide zone, tight folds of the Archean Mary River Group give way down-section to moderately southeast-dipping, highly transposed, high-grade gneissic rocks. Several northeast- and north-striking ductile–brittle faults, some recording normal-sinistral oblique displacement, truncate early gneissosity and folds. This progression, along with U–Pb metamorphic ages, suggests early northwest-directed thrusting, starting at ca. 1.85 Ga, with peak metamorphism in the footwall at ca. 1.83–1.82 Ga. Later extensional displacement caused juxtaposition of lower grade on higher grade rocks. Archean ages of metamorphism (and deformation) are well preserved only in the hanging wall and the youngest metamorphic ages are restricted to the footwall. The data indicate that mountain building involved thrust-related thickening followed by gravitational collapse, a sequence characteristic of Phanerozoic orogens.

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In the Urals region in recent decades, dozens of copper mines, which are the most dangerous in terms of environmental impact, have been closed and flooded. In many of them, acid mine waters continue to form, the concentrations of most components in which exceed the permissible values by several orders of magnitude. The formation of the chemical composition of acidic groundwater has a pronounced unsteady character: a sharp increase in the content of all components in the water after flooding and a gradual decline for many years. On Levikha copper mine (Sverdlovsk region) after filling the depression con in 2007, a site of concentrated discharge of groundwater was formed (technogenic reservoir-a failure in the zone of collapse and displacement). The concentrations of many components 10 years after the completion of flooding are higher than during the development. The analysis of regularities of non-stationary character of hydrogeochemical processes is made on the basis of the data of detailed monitoring and extended definitions of groundwater quality indicators. The main source of acidic water with increased mineralization is the collapse zone, within which the process of drainage for several decades formed technogenic sulfuric acid weathering crust enriched with secondary minerals. According to the data of numerical geofiltration modeling, in the hydrodynamic balance the lateral flow coming from the surrounding areas is 60%, its value is manifested in the dilution of the solution, which is formed in the collapse zone. The time of movement of this flow in the area of collapse is 6–8 years, extremely high values of almost all indicators in the man-made reservoir are observed during this period. According to the inverse physical-chemical modeling (program code Visual MINTEQ ver. 3.0 / 3.1 was used) the composition of rocks, as a result of dissolution-deposition of which underground waters in the area of the flooded mine can be formed, is determined. The duration of the process of formation of acidic groundwater is estimated at tens of years.

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AbstractThe Moine thrust zone of southern Assynt forms part of the northwest margin of the Caledonide belt and has aroused controversy concerning amounts and timing of thrust displacement and sequence of thrust development. Recent mapping shows it to have been a foreland propagating thrust sequence; the uppermost ductile Moine thrust formed first, followed by sequences of imbricates, a major thrust (the Ben More thrust) and then several lower duplex zones. This sequence is clear from new observations that many of the earlier thrusts were folded and/or breached during the development of the underlying structures. A displacement of over 54 km has been estimated for the zone as a whole. An alkaline igneous complex, including the large Borrolan syenite, was intruded during the development of the thrust zone and much of it was carried some 30 km to the west-northwest onto the foreland. Late extensional structures in southern Assynt are an integral part of the Caledonide thrust sequence and probably developed from the collapse of the thrust wedge as it climbed from stronger basem*nt rocks on to a weaker cover sequence on the foreland.

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AbstractThe Rum Igneous Centre comprises two early marginal felsic complexes (the Northern Marginal Zone and the Southern Mountains Zone), along with the later central ultrabasic–basic layered intrusions. These marginal complexes represent the remnants of near-surface to eruptive felsic magmatism associated with caldera collapse, examples of which are rare in the North Atlantic Igneous Province. Rock units include intra-caldera collapse breccias, rhyolitic ignimbrite deposits and shallow-level felsic intrusions, as well the enigmatic ‘Am Màm intrusion breccia’. The latter comprises a dacitic matrix enclosing lobate basaltic inclusions (~1–15 cm) and a variety of clasts, ranging from millimetres to tens of metres in diameter. These clasts comprise Lewisian gneiss, Torridonian sandstone and coarse gabbro. Detailed re-mapping of the Am Màm intrusion breccia has shown its timing of emplacement as syn-caldera, rather than pre-caldera as previously thought. Textural analysis of entrained clasts and adjacent, uplifted country rocks has revealed their thermal metamorphism by early mafic intrusions at greater depth than their present structural position. These findings provide a window into the evolution of the early mafic magmas responsible for driving felsic magmatism on Rum. Our data help constrain some of the physical parameters of this early magma–crust interaction and place it within the geochemical evolution of the Rum Centre.

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In response to orogenic cycles, the ductile shear zone records a complex crustal deformation history. In this study, we conducted a microstructural analysis of two NW–SE trending ductile shear zones (Deokjeok Shear Zone (DSZ) and Soya Shear Zone (SSZ)) in the Late Triassic post-collisional granites along the western Gyeonggi Massif in the Korean Peninsula. The DSZ, overlain by the Late Triassic to the Early Jurassic post-collisional basin fill (Deokjeok Formation), has asymmetric microstructures indicative of a top-down-to-the-northeast shear. Depending on the structural position, the SSZ, which structurally overlies the Deokjeok Formation, exhibits two contrasting styles of deformation. The lower portion of the SSZ preserves evidence of top-up-to-the-southwest shearing after top-down-to-the-northeast shearing; on the other hand, the upper portion only indicates a top-up movement. Given the primary deformation mechanisms of both quartz and feldspar, the deformation temperatures of DSZ and SSZ were estimated at ~300–350 °C and ~350–400 °C, respectively, indicative of the mid-crustal condition. New zircon U-Pb isotopic ages from mylonitic granite in the SSZ and volcanic rocks in the Deokjeok Formation, combined with previously published geochronological data, indicate that the post-collisional granites and volcano-sedimentary sequence were nearly contemporaneous (ca. 223–217 Ma) and juxtaposed because of the Late Triassic orogenic collapse and subsequent new orogenic event. In this study, we highlight the role of the extensional DSZ as a detachment propagated into the middle crust during the Late Triassic orogenic collapse. Our results report a deformational response to a transition from the collisional Songrim Orogeny to the subduction-related Daebo Orogeny in the western Gyeonggi Massif. This, in turn, provides essential insight into cyclic mountain building/collapse in the East Asian continental margin during the Mesozoic time.

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Water inrush in underground mines is a major safety threat for mining personnel, and it can also cause major damage to mining equipment and result in severe production losses. Water inrush can be attributed to the coalescence of rock fractures and the formation of water channel in rock mass due to the interaction of fractures, hydraulic flow, and stress field. Hence, predicting the fracturing process is the key for investigating the water inrush mechanisms for safe mining. A new coupling method is designed in FRACOD to investigate the mechanisms of water inrush disaster (known as “Luotuoshan accident”) which occurred in China in 2010 in which 32 people died. In order to investigate the evolution processes and mechanisms of water inrush accident in Luotuoshan coal mine, this study applies the recently developed fracture-hydraulic (F-H) flow coupling function to FRACOD and focuses on the rock fracturing processes in a karst collapse column which is a geologically altered zone linking several rock strata vertically formed by the long-term dissolution of the flowing groundwater. The numerical simulation of water inrush is conducted based on the actual geological conditions of Luotuoshan mining area, and various materials with actual geological characteristics were used to simulate the rocks surrounding the coal seam. The influences of several key factors, such as in situ stresses, fractures on the formation, and development of water inrush channels, are investigated. The results indicate that the water inrush source is the Ordovician limestone aquifer, which is connected by the karst collapse column to No. 16 coal seam; the fracturing zone that led to a water inrush occurs in front of the roadway excavation face where new fractures coalesced with the main fractured zone in the karst collapse column.

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Samples of the Ionian zone (western Greece) subsurface evaporites, obtained from well cores in salt bodies and in depths ranging from 1000 to 3500m, are texturally studied. Layered halite rocks consisting of chevron-type halite crystals represent most of the specimens. Between the chevron -type halite crystals, which are fluid inclusions-rich, clear halite without inclusions has been diagenetically formed by dissolution and precipitation processes. Anhydrite always accompanies the halite rocks as crystals or nodules. No-occurrence of gypsum has been detected. Along halite grain boundaries dolomite crystals occur. Dolomite grew on halite crystal surfaces as an early diagenetic mineral. Some dolomite crystals are clearly derived by replacement of anhydrite crystals. Halite layers are rich in clay and carbonaceous material favoring reducing environment (presence of pyrite crystals). Chevron-type halite supports accumulation beneath a body of brine, possibly recording annual precipitation cycles. However, its close association with nodular anhydrite cannot exclude the possibility of halite development, in a shallow-water or emergent environment by displacement from capillary brines. Since the studied halite crystals show evidence of mineral replacements and displacement, we suggest an analogous mechanism including accumulation from a standing body of brine and subsequent textural modification in the groundwater zone. Although, Ionian subsurface evaporites have undergone the above-mentioned diagenetical processes, they still reU in their primary textural characteristics. Real brecciation has not been detected in subsurface, except of an in-situ pseudo-brecciation. This observation clearly shows that the outcropping evaporite solution-collapse breccias were formed in the realm of meteoric zone, after the Ionian zone orogenesis.

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Abstract Very low-grade and low-grade metamorphosed basem*nt rocks from distinct inliers of the Africa-derived northwestern Dinarides (Medvednica Mts and Paleozoic Sana-Una Unit, respectively) have been studied with the multigrain step-heating 40Ar/39Ar technique in order to compare and reveal their tectonothermal history. 40Ar/39Ar ages from detrital white mica of the very low-grade basem*nt rocks of the Paleozoic Sana-Una Unit gave a Variscan age of ~335 Ma. The new age is in agreement with 40Ar/39Ar ages from the very low-grade basem*nt exposed at Petrova and Trgovska Gora of the NW Dinarides. Within low-grade metamorphic basem*nt rocks from the Medvednica Mts, we found no Variscan ages. White mica from phyllitic basem*nt rocks of the Medvednica Mts gives predominantly early Alpine ages ranging between 135 and 122 Ma and younger Alpine ages of ~80 Ma. The early Alpine ages of 135 and 122 Ma are interpreted as the date to the onset of ductile nappe stacking predating the formation of Gosau-type collapse basins. The late early Alpine event of ~80 Ma can be traced in the entire Cretaceous-aged orogen of the Circum- Pannonian Region and is synchronous with subsidence of the Gosau-type basins and opening and closure of the neighbouring Sava-Vardar Zone.

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The catastrophic slope failures and landslides that occur in the final stages of lateral collapses of volcanoes destroy much of the evidence for precursory deformation and the early stages of the collapses concerned. Aborted or incomplete collapse structures, although rare, are rich sources of information on these stages of development of catastrophic collapses. The San Andres fault system, on the volcanic island of El Hierro, is a relatively young (between about 545 and about 261–176 ka old) but inactive lateral collapse structure. It appears to represent an aborted giant landslide. It is developed along the flank of a steep-sided volcanic rift zone, and is bounded by a discrete strike-slip fault zone at the up-rift end, closest to the centre of the island. This geometry differs markedly from that of collapse structures on stratovolcanoes but bears some similarities to that of active fault systems on Hawaii. Although the fault system has undergone little erosion, cataclasites which formed close to the palaeosurface are well exposed. These cataclasites are amongst the first fault rocks to be described from volcano lateral collapse structures and include the only pseudotachylytes to have been identified in such structures to date. Their development at unusually shallow depths is attributed to large movements on the fault in a single event, the inferred aborted landslide, and a lack of pressurized pore water. The absence of pressurized fluids in the slumping block may have caused the San Andres fault system to cease moving, rather than develop into a giant volcanic landslide. The recognition that the San Andres fault system is inactive greatly reduces the estimated volcanic hazard associated with El Hierro. However, the lack of evidence for precursory deformation prior to the aborted landslide event is disturbing as it implies that giant lateral collapses can occur on steep-sided oceanic islands with little warning.

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The Coast Mountains orogen is thought to have formed as a result of accretion of the Alexander and Wrangellia terranes against the western margin of the Stikine and Yukon–Tanana terranes, but the nature and age of accretion remain controversial. The Chatham Sound area, which is located along the west flank of the Coast Mountains near the Alaska – British Columbia border, displays a wide variety of relations that bear on the nature and age of the boundary between inboard and outboard terranes. Geologic and U–Pb geochronologic studies in this area reveal a coherent but deformed and metamorphosed sequence of rocks belonging to the Yukon–Tanana terrane, including pre-mid-Paleozoic marble, schist, and quartzite, mid-Paleozoic orthogneiss and metavolcanic rocks, and upper Paleozoic metaconglomerate and metavolcanic rocks. These rocks are overlain by Middle Jurassic volcanic rocks (Moffat volcanics) and Upper Jurassic – Lower Cretaceous strata of the Gravina basin, both of which also overlie Triassic and older rocks of the Alexander terrane. This overlap relationship demonstrates that the Alexander and Wrangellia terranes were initially accreted to the margin of inboard terranes during or prior to mid-Jurassic time. Accretion was apparently followed by Late Jurassic – Early Cretaceous extension–transtension to form the Gravina basin, left-slip along the inboard margin of Alexander–Wrangellia, mid-Cretaceous collapse of the Gravina basin and final structural accretion of the outboard terranes, and early Tertiary dip-slip motion on the Coast shear zone.

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The study is focused on the deformations caused by the impact of water flow in a river channel composed of melt-able permafrost rocks. It is based on the results of laboratory and mathematical simulation. The results of numerical calculations are compared with data of laboratory and field observations. The study shows that a comprehensive and adequate model of river channel deformations should take into account not only ablation, but also other factors, including heat transfer in the soil, sediment transport, and bank slope collapses. Numerical experiments with an improved mathematical model, applied to long time intervals, have shown that the differences between the averaged deformations, calculated by a model of ablation alone, i.e., ignoring bank slope collapses and sediment transport, and a comprehensive model can be considerable. Experiments in a hydraulic flume were good enough to reproduce the effect of delayed collapse, consisting in nonsimultaneous impacts of channel-forming rock melting and a freshet.

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The southern Menderes Massif in southwest Turkey consists mainly of orthogneisses and overlying Palaeozoic–Middle Paleocene schists and marbles. The contact between the two distinct rock types is almost everywhere structural, herein named the southern Menderes shear zone: a S-facing, high-angle ductile shear zone that separates metamorphic rocks of differing grade. Although there is a consensus that the shear zone was associated with top-to-the-S–SSW shearing and is of Tertiary age, its origin and nature have been highly debated over the last decade. Some claim the contact is a thrust fault, while others have argued for an extensional shear zone. Integration of field and microstructural data (the identification of different fabrics, associated kinematics and overprinting relationships) with fission-track thermochronology and the P–T paths of the rocks above and below the shear zone, supports the conclusion that the southern Menderes shear zone is an extensional shear zone and not a thrust. The data are consistent with a model that the exhumation and cooling of the southern Menderes Massif occurred after a period of extensional deformation. Pervasive top-to-the-N–NNE high-temperature–medium-pressure ductile shear structures (D2 deformation) overprint an early HP event (D1 deformation). The subsequent top-to-the-S–SSW greenschist shear band foliation (D3 deformation) developed mostly around the orthogniess–schist contact and forms the most characteristic features of the massif. The top-to-the-N–NNE structures are attributed to the main Alpine constructional deformation that developed during back-thrusting of the Lycian nappes during the latest Palaeogene collision between the Sakarya continent and the Anatolide-Tauride platform across the Neotethyan Ocean. The top-to-the-S–SSW structures are interpreted to be the result of the exhumation of the massif during the activity of the southern Menderes shear zone. The presence of these two distinct fabrics with differing kinematics suggests that the southern Menderes shear zone operated as a top-to-the-N–NNE thrust fault during early Alpine contractional deformation but was later reactivated with an opposite sense of movement (top-to-the-S–SSW) during subsequent Oligocene–Miocene extensional collapse.

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To address the prominent status of great deformation and difficult maintenance of the roadway under high stresses, this study investigated the mechanical characteristics of surrounding rocks and bearing structural stability in a roadway under adjustment and redistribution of stresses through theoretical analysis, numerical simulation, and engineering field test. Stability forms of the bearing structure of roadway surrounding rocks were analyzed by using the axis-changing theory from the perspectives of surrounding rock, mechanical properties of roadways, surrounding rock stress distribution, and mechanical mechanism of the bearing structure. It is suggested that the surrounding rock stress distribution state is improved and the bearing structure is optimized through unloading and reinforcement construction. A mechanical model of roadway excavation was constructed to analyze the influences of excavation spatial effect on the stress releasing and bearing structure of surrounding rocks. A rock postpeak strain softening and dilatation model was introduced to investigate the mechanical characteristics of the surrounding rock mass in the rupture residual zone and plastic softening zone in a roadway. Moreover, we analyzed the influences of unloading and reinforcement construction on the stress path and mechanical characteristics of the rock unit model, which disclosed the adjustment mechanism of the bearing structure of surrounding rocks by the failure development status of rocks. A numerical simulation on the distribution of surrounding rock stress fields and adjustment features of the bearing structure after roadway excavation and unloading and reinforcement construction was carried out by using the FLAC3D program. Results demonstrate that the unloading construction optimizes the axial ratio of spatial excavation in a roadway and the reinforcement zones on both sides are the supporting zones of the bearing structure. Moreover, the ratio between the distance from two side peaks to the roadway sides and the distance from the roof and floor peaks to the excavation space is equal to the coefficient of horizontal pressure. In other words, the final collapse failure mode of surrounding rock is that the long axis of the excavation unloading space points to the same direction with the maximum principal stress of the primary rock. Reinforcement forces the surrounding rocks to form a “Ω-shaped” bearing structure, which is in favor of the long-term maintenance of the roadway.

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The paper considers the dependence of the mechanical speed of wells drilling on the seams with abnormally high spatial (reservoir) pressures. Forecasting of AHRP is important for improving the degree of completion of layers in process of drilling. As a result of the drilling in of unpredictable areas of AHRP in the Pre-Carpathian region the drill columns often get stuck, one of the reasons for which is not often a justified preventive weighting of the drilling mud. To regulate the pressure in the well during drilling, it is necessary to identify the upper limit of the AHRP zone in time and give it a reasonably quantified characteristics. After analysying the data of wells in the Pre-Carpathian region and those that are being drilled now, it was possible for us to establish that in the case of approaching the well bore to the formation of AHRP, there is an increase in the mechanical speed of drilling in clay rocks, due to the presence of increased inernal pressure and a lower density of these rocks. Increasing of the mechanical speed of drilling under the condition of constant parameters of the drilling regime is also due to heterogeneity of rocks, and stratigraphic transitions from one fold to the other. However, in the case of a double increase of the mechanical speed of drilling in sedimentary layers which are identical in lithology, it is possible to confidently explain this phenomenon by the entrance of the borehole into the AHRP zone. In order to verify the possibility of using mechanical logging to predict the areas of AHRP directly during drilling, we compared the change in the mechanical speed of drilling along the well bore with the data of quantitative and qualitative determination of the areas of AHRP on the results of industrial-geophysical research. Qualitative and quantitative estimation of AHRP zones was carried out, basically, according to the data of electrometry of wells, using the technique of "curves of normally densified clay". For the verification of the findings, direct measurements of the formation pressure with the pressure gauges were used and the data of determination of the formation pressures in the case of transfer of clay solution from the well. Due to the prediction of spatial and reservoir pressures by means of mechanical logging in the process of well laying, we observe a decrease in accidents rate, and an increase in the efficiency of drilling.

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The results of laboratory studies of the elastic-strength properties of cement stone samples depending on the hardening time and the effect of an acid reagent, and approximated dependences of the change in the elastic modulus, Poisson's ratio and strength properties, depending on the time characteristics for two types of plugging materials are presented. A finite element scheme of the nearwellbore zone has been developed, taking into account the cement stone and the production casing. The results of numerical modeling of the stress-strain state of columns with a diameter of 146 and 178 mm, cement stone and reservoir rocks near the well based on an elastic model are presented. The analysis of the stress field for the occurrence of zones of destruction in the cement stone using the Coulomb-Mohr criterion is carried out. It is shown that, depending on the time of hardening and the effect of an acidic reagent, cement does not collapse and retains a sufficient safety factor. Keywords: cement stone; plugging material; elastic-strength properties; near-wellbore zone; numerical model; finite element method; stress-strain state; safety factor.

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A major zone of deformation affects Early Carboniferous rocks in the southern part of the Maritimes Basin of Nova Scotia, close to the boundary between the Avalon and Meguma terranes of the Appalachians. Field relationships at Cheverie indicate thrusting of Tournaisian Horton Group clastics over Viséan Windsor Group carbonates, evaporites, and clastics, a relationship confirmed by the Cheverie #01 well. Mapped relationships to the south indicate that a system of thrusts, here termed the Kennetcook thrust system, climbs upsection to the southeast, becoming a décollement within Windsor Group evaporites. Industry seismic profiles clearly show deformed Windsor Group, and include fold and fault structures indicative of evaporite flow and solution collapse. Below the Windsor Group, half-grabens filled with Horton Group are clearly imaged; offsets at graben-related faults show that these structures were inverted during later shortening. Above the Windsor Group, less deformed rocks of the Pennsylvanian Scotch Village Formation (Cumberland Group) fill minibasins created by the withdrawal or solution of deformed Windsor evaporites. The timing of thrusting is constrained by these relationships and by crosscutting intrusions to a narrow interval around the Mississippian–Pennsylvanian boundary prior to ∼315 Ma. Deformation was probably related to dextral transpression along the former Avalon–Meguma boundary. Depending on how shortening was transmitted to the southeast, up to 1500 km2 of southern mainland Nova Scotia may be underlain by tectonically transported rocks.

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In the southern Quebec Appalachians, the early tectonic history of the Laurentian margin (Humber zone) comprises foreland-propagating, northwest-directed thrust faulting, nappe emplacement, and regional prograde metamorphism in response to the obduction of large ophiolitic nappes during the Taconian orogeny. In the internal Humber zone, this event is dated at 462 ± 3 Ma (late Middle Ordovician), which is interpreted to represent the timing of near-peak Taconian metamorphism. Superimposed hinterland-directed structures are accompanied by retrograde metamorphism and consist of back thrusts and normal faults, which respectively delimit the northwestern and southeastern limbs of the Sutton and Notre-Dame mountains anticlinoria, both salient structures of the internal Humber zone of southern Quebec. Geochronologic data on the timing of hinterland-directed deformation vary from 431 to 411 Ma. Two tectonic models are presented and discussed, which may account for the Silurian – Early Devonian evolution of the Laurentian margin: (1) back thrusting and syn- to post-compressional crustal extension in response to the tectonic wedging of basem*nt-cored duplexes inducing delamination of supracrustal rocks; (2) tectonic exhumation of the internal Humber zone by extensional collapse. Evidence for Silurian – Early Devonian extensional tectonism in the Humber zone provides the basem*nt infrastructures necessary for the creation and the onset of sedimentation in the Gaspé Belt basins (e.g., Connecticut Valley – Gaspé synclinorium). Several structural, metamorphic features in the internal Humber zone of the northwestern New England Appalachians yield analogous characteristics with those of southern Quebec and may have shared a similar Silurian – Early Devonian tectonic evolution.

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Abstract The Azuero Peninsula, located in SW Panama, is a region characterized by a long-lived intra-oceanic subduction zone. Volcanism began in Late Cretaceous time, as the result of subduction of the Farallon plate beneath the Caribbean plate. Usually, ancient volcanic arcs related to intra-oceanic subduction zones are not preserved, because they are in areas with difficult access or covered by modern volcanic arc material. However, on the Azuero peninsula, a complete section of the volcanic arc together with arc basem*nt rocks provides the opportunity to study the sedimentation and volcanism in the initial stages of volcanic arc development. The lithostratigraphic unit which records fore-arc evolution is the “Río Quema” Formation (RQF), a volcanic apron composed of volcanic and volcaniclastic sedimentary rocks interbedded with hemipelagic limestones, submarine dacite lava domes, and intruded by basaltic-andesitic dikes. The “Río Quema” Formation, interpreted as a fore-arc basin infilling sequence, lies discordantly on top of arc basem*nt rocks. The exceptionally well exposed arc basem*nt, fore-arc basin, volcanic arc rocks and arc-related intrusive rocks provide an unusual opportunity to study the relationship between volcanism, sedimentation and magmatism during the arc development, with the objective to reconstruct its evolution. The “Río Quema” Formation can be divided into three groups: 1) proximal apron, a sequence dominated by lava flows, interbedded with breccias, mass flows and channel fill, all intruded by basaltic dikes. The rocks represent the nearest materials to the volcanic source, reflecting a coarse sediment supply. This depositional environment is similar to gravel-rich fan deltas and submarine ramps; 2) medial apron, characterized by a volcanosedimentary succession dominated by andesitic lava flows, polymictic volcanic conglomerates and crystal-rich sandstones with minor pelagic sediments and turbidites. These rocks were deposited from high-density turbidity currents and debris flows, directly derived from erupted material and gravitational collapse of an unstable volcanic edifice or volcaniclastic apron; 3) distal apron, a thick succession of sandy to muddy volcaniclastic rocks, interbedded with pelagic limestones and minor andesitic lavas, intruded by dacite domes and by basaltic to andesitic dikes. Bedforms and fossils suggest a quiet, relatively deep-water environment characterized by settling of clay and silt (claystone, siltstone) and by dilute turbidity currents of reworked volcaniclastic detritus. The timing of the initial stages of the volcanic arc has been constrained through a biostratigraphic study, using planktonic foraminifera and radiolarian species. The fossil assemblage indicates that the age of the “Río Quema” Formation ranges from Late Campanian to Maastrichtian, providing a good constraint for the development of the volcanic arc and volcaniclastic apron, during the initial stages of an intra-oceanic subduction zone.

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The high-grade metamorphic complexes along the northern Moldanubian periphery of the central Bohemian Massif provide an outstanding structural record of all episodes of the collisional evolution of the Variscan Orogeny. The kinematics and timing of the orogenic processes were examined by structural and microstructural studies of middle and lower crustal rocks combined with xenotime and monazite geochronology. Four distinct tectonic events were identified. A first relict sub-horizontal fabric S1 associated with high-pressure–high-temperature metamorphism was only developed in the lower crustal rocks and was related to back-arc extension or lower crustal flow in a supra-subduction domain. This fabric was completely reworked to the subvertical foliation S2 at c. 340 Ma by major collisional thickening, leading to juxtaposition of the lower and middle crust. Thereafter, extensional collapse of the thickened orogenic system caused strong refolding to the high-temperature sub-horizontal fabric at c. 325 Ma. The region was subsequently affected by NNE–SSW-oriented horizontal shortening related to dextral shearing and the clockwise rotation of crustal blocks adjacent to the large-scale dextral shear zone (the Elbe Zone). This led to fragmentation and reorientation of the Moldanubian margin to its current position.Supplementary material: A summary of the main microstructural features related to the defined deformation phases, the results of the U–Pb laser ablation inductively coupled plasma mass spectrometry analyses of xenotime and monazite, back-scattered electron images and rare earth element compositional maps are available at https://doi.org/10.6084/m9.figshare.c.5708800.v1

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The Flin Flon – Kisseynew boundary in the eastern Trans-Hudson Orogen is interpreted here as an early thrust fault that places 1.86–1.84 Ga Kisseynew belt turbidites over previously deformed 1.91–1.88 Ga arc and ocean-floor assemblages of the Flin Flon belt. The basin in which sedimentary rocks of the Kisseynew belt were deposited has been interpreted to have formed partly within the Flin Flon belt. The fault that juxtaposes the two belts is interpreted to have been localized near the ancestral basin margin, resulting in development of a major ramp zone during basin closure. This interpreted ramp zone provides an explanation for the steep to shallow structural transition that corresponds to increasing metamorphic grade. Collapse of the Kisseynew sedimentary basin and juxtaposition of the two belts are attributed to southwest-verging folding and thrusting that initiated prior to emplacement of 1.83 Ga plutons. This magmatism was followed by regional greenschist- to upper-amphibolite-grade metamorphism (1.82–1.805 Ga) and renewed southwest-directed folding and thrusting. Late backfolds developed at the leading edge of the fold-thrust belt. Postpeak metamorphic deformation resulted in large-scale, upright folding of the fold–thrust stack (including the Flin Flon – Kisseynew boundary). This stage of deformation is interpreted to record a transition from southwest-directed transport to northwest-southeast-directed shortening at ~1.8 Ga.

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Production of uranium by the method of bore-hole mining (BHM) is carried out from productive water-bearing formations represented by sands of various sizes. The beds are opened by the process well drilling using bentonite clay mud. This is accompanied by colmatation of the near-filter zone (NFZ) rocks. The performed studies showed the need for the complete removal of clay mud from the NFZ at the stage of well construction. It is shown that this can be done by the methods of interval-by-interval filter development or by the collapse of the productive horizon sands when NFZ after-filter washing with technical water. Laboratory tests on the chemical resistance of bentonite sleeves to the acid solutions action were carried out. Geological and process conditions for the use of bentonite sleeves for waterproofing the bore-hole annulus of process BHM wells were defined.

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Groundwater inrush is a typical hydrologic natural hazard in mining engineering. Since 2000 to 2012, there have been 1110 types of mine groundwater inrush hazards with 4444 miners died or missing. As a general geological structure in the northern China coalfields, the karst collapse pillar (KCP) contains a significant amount of granular rocks, which can be easily migrated under high hydraulic pressure. Therefore, the KCP zone acts as an important groundwater inrush pathway in underground mining. Grouting the KCP zone can mitigate the risk of groundwater inrush hazard. However, the fracture or instability of the coal pillar near KCP can cause the instability of surrounding rock and even groundwater inrush hazard. To evaluate the risk of groundwater inrush from the aquifer that is caused by coal pillars instability within grouted KCP in a gob, an in-situ investigation on the deformation of the surrounding strata was conducted. Besides, a mechanical model for the continuous effect on the coal pillar with the floor-pillar-roof system was established; then, a numerical model was built to evaluate the continuous instability and groundwater inrush risk. The collective energy and stiffness in the floor-pillar-roof system are the two criterions for judging the stability of the system. As a basic factor to keep the stability of floor-pillar-roof system, the collective energy in coal pillar is larger than that in floor-roof system. Moreover, if the stiffness of floor-roof or coal pillar meets a negative value, the system will lose stability; thus, the groundwater inrush pathway will be produced. However, if there is a negative value occurring in floor-pillar-roof system meets, it indicates that the system structure is situated in a damage state; a narrower coal pillar will enlarge the risk of continuous instability in the system, leading to a groundwater inrush pathway easily. Continuous coal pillars show a lower probability of instability. Conversely, the fractured coal pillars have a greater probability of failure. The plastic zone and deformation of the roadway roof in the fractured coal pillar are larger than that of continuous coal pillar, indicating that the continuous coal pillars mitigate the risk of groundwater inrush hazard effectively.

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The Araçuaí belt corresponds to the external portion of the western half of the Araçuaí-West Congo Neopro-terozoic orogen. TheAraçuaí belt fringes the São Francisco craton to east and is separated from the crystalline core of the orogen by the Abre Campo geophysical discontinuity. The southern Araçuaí belt involves four major lithologic units: the Archean and Paleoproterozoic gneisses of the Mantiqueira Complex, the Pedra Dourada Charnockite, the Paleoproterozoic Borrachudos Granitoid, and the metavolcanosedimentary rocks of the Dom Silvério Group. The Dom Silvério Group occurs in a NNE-SSW striking belt and consists of a thick package of metapelitic rocks with intercalations of quartzites, amphibolites, meta-ultramafics, banded iron formations, gondites and marbles. All units of the southern Araçuaí belt underwent four syn-metamorphic phases of deformation in the course of the Brasiliano event. The first phase, synchronous to a regional amphibolite facies metamorphism, was associated to a general tectonic transport towards north along the left-lateral Dom Silvério shear zone and its low angle segment. The second and third phases represent progressive stages of a west directed shortening, which led to the development of local thrusts and pervasive folds in several scales. The fourth phase is extensional and reflects the collapse of the orogen.

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Karst manifestations are widespread in many regions and pose a significant danger to residence and economic activity. Failing funnels arise during the collapse of rocks over underground voids (caves, workings, etc.), formed during karst formation or in the process of anthropogenic doing in the rock massive. However, not every karst or technogenic cavity gives rise to a failure of the earth’s surface, and as a rule, its occurrence is unexpected. In this work, we consider the dynamics of the formation of dips of the earth’s surface in the form of a collapse pipe. To do this, the geomechanical problem is solved by the meshless code Smoothed Particle Hydrodynamics (SPH). The method allows to obtain a solution to the problem taking into account large deformations and possible discontinuities in the process of changing the stress-strain state. The Drucker-Prager fracture criterion is used, the parameters of which change over time in accordance with the accumulation of damage, which determines the temporary development of the fracture process, its beginning and speed. Various options for the formation of a vertical dip are considered depending on the geometrical parameters of the initial cavity, its depth and materials composing the rock mass, as well as the features of the destruction of various materials composing the mass during the formation of the dip. Relations are obtained that relate the depth of the cavity, the horizontal size of the hole, the strength properties of the rocks (adhesion, angle of internal friction), the coefficient of lateral pressure in the array. The features of wave processes generated by the formation of a dip are considered, for which a velocity field is obtained near the fracture zone at various time points in the fracture process.

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The North Dabie complex zone (NDZ), central China, is a high-T ultrahigh-pressure (UHP) metamorphic terrane. It underwent a complex evolution comprising of multistage metamorphism and multiple anatectic events during the Mesozoic continental collision, characterized by granulite-facies overprinting and a variety of migmatites with different generations of leucosomes. In this contribution, we carried out an integrated study including field investigation, petrographic observations, zircon U-Pb dating, and whole-rock element and Sr-Nd-Pb isotope analysis for the migmatites in the NDZ and their leucosomes and melanosomes. As a result, four groups of leucosomes have been recognized: Group 1 (garnet-bearing leucosome), strongly deformed leucosomes with coarse-grained peritectic garnet; Group 2 (amphibole-rich leucosome), weakly deformed to undeformed amphibole-rich leucosomes with coarse-grained peritectic amphibole and no garnet; Group 3 (amphibole-poor leucosome), weakly deformed to undeformed amphibole-poor leucosomes with minor fine-grained amphibole; Group 4 (K-feldspar-rich leucosome), K-feldspar-rich leucosomes mainly composed of coarse-grained quartz, plagioclase and K-feldspar. Zircon SHRIMP and LA-ICPMS U-Pb dating suggest that the Group 1 leucosomes formed at 209 ± 2 Ma whereas the rest of the leucosome groups (Groups 2–4) occurred between 145–110 Ma, in response to decompression under granulite-facies conditions during the early stage of exhumation, and to heating during post-orogenic collapse, respectively. Furthermore, the garnet-bearing leucosomes were resulted from fluid-absent anatexis related to biotite dehydration melting, while the other three groups of leucosomes were formed during large-scale fluid-present partial melting and coeval migmatization. This migmatization comes from heating from the mountain-root removal and asthenosphere upwelling, together with the influx of fluids derived from country rocks at mid-upper crustal levels. However, all the leucosomes and melanosomes display Pb-isotopic compositions similar to those observed for the NDZ UHP rocks (eclogites and granitic gneisses), suggesting a common source from the Triassic subducted Neoproterozoic lower-crustal rocks. In addition, the Cretaceous partial melting and migmatization began at 143 ± 2 Ma with three age-peaks at 133 ± 3 Ma, 124 ± 3 Ma and 114 ± 7 Ma, respectively.

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AbstractWe focus on an active continental margin related to northwards subduction during the Eocene in which sedimentary melange (‘olistostromes’) forms a key component. Maastrichtian – Early Eocene deep-marine carbonates and volcanic rocks pass gradationally upwards into a thick succession (<800 m) of gravity deposits, exposed in several thrust sheets. The lowest levels are mainly siliciclastic turbidites and debris-flow deposits. Interbedded marls contain Middle Eocene planktonic/benthic foraminifera and calcareous nannofossils. Sandstones include abundant ophiolite-derived grains. The higher levels are chaotic debris-flow deposits that include exotic blocks of Late Palaeozoic – Mesozoic neritic limestone and dismembered ophiolite-related rocks. A thinner sequence (<200 m) in one area contains abundant redeposited Paleogene pelagic limestone and basalt. Chemical analysis of basaltic clasts shows that some are subduction influenced. Basaltic clasts from unconformably overlying alluvial conglomerates (Late Eocene – Oligocene) indicate derivation from a supra-subduction zone ophiolite, including boninites. Taking account of regional comparisons, the sedimentary melange is interpreted to have formed within a flexurally controlled foredeep, floored by continental crust. Gravity flows including large limestone blocks, multiple debris flows and turbidites were emplaced, followed by southwards thrust imbrication. The emplacement was possibly triggered by the final closure of an oceanic basin to the north (Alanya Ocean). Further convergence between the African and Eurasian plates was accommodated by northwards subduction beneath the Kyrenia active continental margin. Subduction zone rollback may have triggered collapse of the active continental margin. Non-marine to shallow-marine alluvial fans prograded southwards during Late Eocene – Oligocene time, marking the base of a renewed depositional cycle that lasted until latest Miocene time.

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In underground mining engineering, rocks around the entry are always subjected to large plastic deformation disasters, such as supporting body failure, roof rock collapse, and even rock burst under abutment stress and dynamic stress. To improve the stability of these rocks, the entry layout under abutment stress and dynamic stress (ELAD) method was put forward to protect the entry from high abutment stress and dynamic stress. Dynamic disturbance intensity (DDI) was determined as the key evaluation index in ELAD, which was divided into “Slightly Disturbed Type,” “Moderately Disturbed Type,” and “Violent Impact Type” by the dynamic disturbance threshold (DDT) and dynamic large-deformation threshold (DLT). The established servo calculation algorithm was applied into a dynamic and static numerical analysis model with FLAC3D500 software for the solving of DDT and DLT by the method of zero growth DDI of plastic failure zone and the engineering-permitted limitation deformation. This model was validated by comparing the displacement of entry with the measured results in the field. The model results validated that the entry should keep away from the dynamic stress of Violent Impact Type firstly and then be arranged in the zone where the dynamic stress belongs to Slightly Disturbed Type. DDT increases linearly and DLT decreases with a power function as the increasing of the abutment stress. ELAD method is reliable to protect this kind of underground entry and its applicability will be improved by the support resistance by comparing the results from ELAD with those from the widely used methods for field investigation discussion. The analysis procedure can be repeatable and necessary since the rock and coal materials may be different in geological and engineering conditions.

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As part of a regional study of the evolution of the Otway Basin, the Investigator 3D seismic survey has been structurally analysed, using 11 extracted 2D sections and 3D interpretations of key horizons. South-southwest directed extension was widespread in the Turonian forming the Shipwreck Trough, coincident with uplift of the Otway Ranges to the northeast. The Turonian extension, at ~1.5 myrs, resulted in planar faults in the northeastern part of the Trough, but large half-graben above south-southwest dipping listric master faults in the southwest, both fault sets soling into an Early Cretaceous shale detachment. The half-graben propagated north from the Mussel-Tarpwaup Hinge-Zone by footwall collapse and accommodated deposition of reservoir rocks for the known hydrocarbon accumulations. The half-graben die out along strike to the east at tip-points against an accommodation zone that developed into a continental transform (the Shipwreck Fault).Santonian breakup in the Great Australian Bight coincided with considerable south-southwesterly extension in the Otway Basin juxtaposed against the failed Bassian rift across the Shipwreck Fault. Extension of ~1.21 km to the west of the Shipwreck Fault contrasts with ~0.42 km on the eastern side accommodated by ~0.79 km left-lateral displacement along the Shipwreck Fault. The Belfast Mudstone was deposited during this time, forming the regional seal for the known hydrocarbon accumulations.Limited slow extension during the Campanian to Early Eocene resulted in a further 0.33 km sinistral slip along the Shipwreck Fault. Late Early Eocene Breakup in the Otway Basin ended the transitional phase, terminating extensional and Shipwreck Fault offset. The breakup caused local uplift and ~1 km erosion of Wangerrip Group sediments. The post breakup phase is characterised by prograding sequences indicating progressive-regressive cycles.The Thylacine and La Bella gas fields occur in large tilted fault-blocks near the Hinge-Zone. These successful large structures lie along a longstanding High probably sourced from south of the Hinge-Zone. Key elements for a successful hydrocarbon play are deposition of the Turonian Waarre Formation sandstone reservoirs at rift onset and of a thick Belfast Mudstone seal during continuous Coniacian-Santonian extension. Footwall collapse north of the Hinge-Zone, bound by the deepwater Otway Basin and the continental transform, controlled the distribution of traps, regional seal and hydrocarbon maturation.

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Abstract The Nautanen deformation zone in the Gällivare area of northern Sweden is a highly Cu-mineralized, magnetite-rich, large-scale shear zone with a long-lived (~100 m.y.) deformation, hydrothermal alteration, and mineralization history. This composite structure hosts the Aitik porphyry Cu-Au-Ag ± Mo deposit and several Cu-Au ± Fe ± Ag ± Mo occurrences assigned to the iron oxide copper-gold (IOCG) deposit class. The Nautanen deformation zone was a locus for polyphase deformation and intermittent metasomatic-hydrothermal activity that overprinted middle Orosirian (ca. 1.90–1.88 Ga) continental arc-related volcanic-plutonic rocks. The deformation zone is characterized by intense shearing fabrics that form a series of subvertical to moderately W-dipping, NNW-SSE–trending, first-order shear zones with oblique reverse kinematics and related NNE-SSW–oriented second-order shear zones that control hydrothermal alteration patterns and Cu-Au mineralization. Hydrothermal alteration in the study area formed during several phases. Volcanic-volcaniclastic rocks to the east and west of the Nautanen deformation zone display low to moderately intense, pervasive to selectively pervasive (i.e., patchy zones or bands, disseminations) sericite ± feldspar, amphibole + biotite + magnetite ± tourmaline, and K-feldspar + hematite alteration. Both the amphibole + biotite and K-feldspar + hematite associations occur adjacent to NNW- and NE-oriented deformation zones and are locally associated with minor sulfide. Within the deformation zone, a moderate to intense biotite + amphibole + garnet + magnetite + tourmaline + sericite alteration assemblage is typically associated with chalcopyrite + pyrrhotite + pyrite and forms linear and subparallel, mainly NNW-oriented seams, bands, and zones that locally appear to overprint possibly earlier scapolite + sericite ± feldspar alteration. Late-stage epidote ± quartz ± feldspar alteration (retrograde saussuritization) forms selectively pervasive zones and epidote veinlets across the area and is partly related to brittle faulting. A magnetite-amphibole-biotite–rich, penetrative S1 foliation records shortening during early Sveco*karelian-related deformation (D1) and can be related to ca. 1.88 to 1.87 Ga arc accretion processes and basin inversion that overlaps with regional peak metamorphism to near mid-amphibolite facies conditions and a potential initial Cu mineralization event. Folding and repeated shearing along the Nautanen deformation zone can be assigned to a second, late-Sveco*karelian deformation event (D2 stage, ca. 1.82–1.79 Ga) taking place at a higher crustal level. This D2 deformation phase is related to late-stage accretionary processes active during a transition to a stage of postorogenic collapse, and it was accompanied by abundant, syntectonic intrusions. D2-related magmatism produced high-temperature and low-pressure conditions and represents a regional magmatic-hydrothermal event that controlled the recrystallization/remobilization of magnetite, biotite, and amphibole. Associated shear zone reactivation during D2 favors the utilization of the Nautanen deformation zone as a fluid conduit, which preferentially controlled the siting and formation of epigenetic Cu-Au mineralization with distinctive IOCG characteristics within second-order shear zones.

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We present here a tectonic-geodynamic model for the generation and flow of partially molten rocks and for magmatism during the Variscan orogenic evolution from the Silurian to the late Carboniferous based on a synthesis of geological data from the French Massif Central. Eclogite facies metamorphism of mafic and ultramafic rocks records the subduction of the Gondwana hyperextended margin. Part of these eclogites are forming boudins-enclaves in felsic HP granulite facies migmatites partly retrogressed into amphibolite facies attesting for continental subduction followed by thermal relaxation and decompression. We propose that HP partial melting has triggered mechanical decoupling of the partially molten continental rocks from the subducting slab. This would have allowed buoyancy-driven exhumation and entrainment of pieces of oceanic lithosphere and subcontinental mantle. Geochronological data of the eclogite-bearing HP migmatites points to diachronous emplacement of distinct nappes from middle to late Devonian. These nappes were thrusted onto metapelites and orthogneisses affected by MP/MT greenschist to amphibolite facies metamorphism reaching partial melting attributed to the late Devonian to early Carboniferous thickening of the crust. The emplacement of laccoliths rooted into strike-slip transcurrent shear zones capped by low-angle detachments from c. 345 to c. 310 Ma is concomitant with the southward propagation of the Variscan deformation front marked by deposition of clastic sediments in foreland basins. We attribute these features to horizontal growth of the Variscan belt and formation of an orogenic plateau by gravity-driven lateral flow of the partially molten orogenic root. The diversity of the magmatic rocks points to various crustal sources with modest, but systematic mantle-derived input. In the eastern French Massif Central, the southward decrease in age of the mantle- and crustal-derived plutonic rocks from c. 345 Ma to c. 310 Ma suggests southward retreat of a northward subducting slab toward the Paleotethys free boundary. Late Carboniferous destruction of the Variscan belt is dominantly achieved by gravitational collapse accommodated by the activation of low-angle detachments and the exhumation-crystallization of the partially molten orogenic root forming crustal-scale LP migmatite domes from c. 305 Ma to c. 295 Ma, coeval with orogen-parallel flow in the external zone. Laccoliths emplaced along low-angle detachments and intrusive dykes with sharp contacts correspond to the segregation of the last melt fraction leaving behind a thick accumulation of refractory LP felsic and mafic granulites in the lower crust. This model points to the primordial role of partial melting and magmatism in the tectonic-geodynamic evolution of the Variscan orogenic belt. In particular, partial melting and magma transfer (i) triggers mechanical decoupling of subducted units from the downgoing slab and their syn-orogenic exhumation; (ii) the development of an orogenic plateau by lateral flow of the low-viscosity partially molten crust; and, (iii) the formation of metamorphic core complexes and domes that accommodate post-orogenic exhumation during gravitational collapse. All these processes contribute to differentiation and stabilisation of the orogenic crust.

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The dolostones of the Oligocene–Miocene Bluff Formation on the Cayman Islands are characterized by well-developed surficial, interface, and subsurface karst features that are open or filled with speleothems and sediment.Some of the open caves show evidence of a minimum of two stages of development related to dissolution in the phreatic zone and the vadose zone. The development of speleothemic formations (e.g., stalactites, stalagmites, columns) is limited in some caves but extensive in others. Some of the caves have limited amounts of sediment on their floors. In these caves, the speleothems and sediments are still formed of CaCO3 and thus contrast sharply with the dolostone of the Bluff Formation in which they occur. Some of the joints, sinkholes, and caves are filled with breccia, caymanite, terra rossa, terra rossa breccia, pisolitic limestone, and speleothems. Although filled, such karst features are analogous to the open karst features that occur elsewhere on the islands. The filling of joints, sinkholes, or caves is not directly related to the age of the karst development, since caves of the same age may be open or filled. This suggests that local conditions, such as the availability of sediment or the nature of the waters flowing through the caves, played an important role in determining whether a karst feature is filled.Surficial karst features have a low preservation potential, whereas interface and subsurface karst features have a high preservation potential in some circ*mstances. In the case of sinkholes this assumes that later transgressions did not remove the upper part of the rock body that contained the filled sinkholes. For caves this assumes that they were filled with speleothems and sediment prior to their reaching such a size that collapse of the overlying strata occurred because of the lack of support. If collapse occurs, the presence of caves can only be inferred from the resultant collapse breccias. A potentially valuable criterion for the recognition of paleokarst may lie in the fact that the rocks filling open karst features (e.g., joints, sinkholes, caves) may contrast sharply with the host strata in terms of both lithology and age.

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The mechanical behaviours of layered rock mass exhibit significant differences in the directions parallel and vertical to the bedding planes. The deformation and failure of a layered rock mass has remarkable weak-plane dependence, which brings a major challenge to the control of the stability of the surrounding rock mass in underground openings. In this study, a layered rock mass is firstly regarded as a composite material composed of interlayered rocks and bedding planes. Then, based on the Mohr–Coulomb and maximum tensile stress criteria, an index of point safety factor for a layered rock mass is established considering the mechanical properties of interlayered rocks and bedding planes. The safety of the artificial layered rock mass specimens in the triaxial test is evaluated using this index. The results show that the distribution of this index is in good agreement with the macroscopic failed zone of the rock specimen, indicating that this index is feasible for characterizing the macroscopic failure of rock masses. Finally, the index is adopted to evaluate the stability of the midpartition between the #3 and #4 diversion tunnels at the right bank of the Wudongde hydropower station before and after its reinforcement. The results indicate that there is a yielded zone where the point safety factor is less than 1.0 in the unreinforced midpartition of the collapsed tunnel section, and it is nearly connected. If it is not reinforced in time, collapse cut-through of the entire midpartition may occur and then endanger the overall stability of the tunnel. After the emergency reinforcement measure with two-ended anchored piles and concrete backfill, the safety of the midpartition is significantly improved. In this case, the safety factor is much larger than 1.0, indicating that the adoption of this emergency reinforcement measure is effective.

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Paikon and Tzena terranes are situated in the centre part of Axios zone, between Almopia and Paionia ophiolitic belts. Tectonostratigraphic data reveal that both have been affected by the same polyphase deformation and metamorphism, as well that they have the same lithostratigraphic column. The first deformation phase took place during the Middle to Late Jurassic and is associated with ophiolite obduction, nappe- stacking, terrane accretion and crustal thickening (D1). Metamorphism does not exceed greenschist facies (M1). Relict HP-LT metamorphic assemblages predating M1 metamorphism are possibly developed during subduction processes and overloading of the obducted ophiolites on the continental margin, characterized the initial stages of deformation. Compressional tectonics and intense thrusting with the same kinematics continued in Lower Cretaceous time, affected all pre-Upper Cretaceous units and the obducted ophiolites (D2). This phase is associated with low-greenschist metamorphism (M2). The first main extensional event occurs in the Late Cretaceous, related to basin formation and sedimentation (D3). During Paleocene to Eocene, D4 intense imbrication of all tectonic units towards mainly SW takes place again. Nappes collapse and finally crustal exhumation taken place during Oligocene to Miocene, associated with low - angle normal faults, with a main top to the SW sense of movement (D5). In Miocene to recent times, high - angle normal and strike-slip faults are formed in an extensional to transtensional strain regime (D6), associated with Neogene to Quaternary basin formation and terrane dispersion. The basem*nt rocks of both terranes are of Pelagonian origin, exhumed as a multiple tectonic window.

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Abstract. This study describes the methodology carried out and the main results achieved when using photogrammetry and Terrestrial Laser Scanning (TLS) to obtain 3D models of the evolution of archaeological works in Egyptian tombs. More concretely, the study was performed in the exterior zone of the QH34 set of tombs located in the necropolis of Qubbet el-Hawa (Aswan, Egypt). The necropolis is composed of tens of rock-cut tombs located in a medium-size hill situated on a bank of the Nile River. The QH34 zone concentrates a great quantity of tombs from several periods of ancient Egypt. The area of study is situated on a horizontal platform of the terrain of about 300 m2. Thanks to the particular geology of this zone, with a fracture that caused the collapse of part of the rocks, much of these tombs have remained intact because the remains of the collapsed terrain hid their entrances. The archaeological works were carried out during two periods (2018 and 2019 campaigns). The main goal of this study was to model the evolution of these works using several geomatic techniques and obtaining several 3D models of the terrain and burial elements to document the previous, intermediate and final status and to analyse the archaeological works undertaken. In addition, a reduced time was demanded for the acquisition of data. The methodology developed has demonstrated its viability for performing multi-temporal studies in order to document the evolution of the excavation, providing a wide and reliable set of geomatic products.

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Sand production is one of the major issues in the development of reservoirs in poorly cemented rocks. Geomechanical modeling gives us an opportunity to calculate the reservoir stress state, a major parameter that determines the stable pressure required in the bottomhole formation zone to prevent sand production, decrease the likelihood of a well collapse and address other important challenges. Field data regarding the influence of water cut, bottomhole pressure and fluid flow rate on the amount of sand produced was compiled and analyzed. Geomechanical stress-state models and Llade’s criterion were constructed and applied to confirm the high likelihood of sanding in future wells using the Mohr–Coulomb and Mogi–Coulomb prototypes. In many applications, the destruction of the bottomhole zone cannot be solved using well mode operations. In such cases, it is necessary to perform sand retention or prepack tests in order to choose the most appropriate technology. The authors of this paper conducted a series of laboratory prepack tests and it was found that sanding is quite a dynamic process and that the most significant sand production occurs in the early stages of well operation. With time, the amount of produced sand decreases greatly—up to 20 times following the production of 6 pore volumes. Finally, the authors formulated a methodological approach to sand-free oil production.

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We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.