Thrust Deformation Research Articles

Oil-and-gas potential of the northeast Predpatom trough

This article discusses the geological structure and prospects of the oil and gas potential in the northeastern part of the Predpatom trough. The materials of the study included geological findings from deep drilling and data from direct geochemical studies conducted in recent years. It describes the specific features of the structural plans of the upper versus the lower part of the geological cross-section. It is assumed that deep drilling in the area of the Ulugur structure has not reached the target productive horizons in the autochthonous part of the section. After acquiring more recent seismic data, there is a proposal to drill a deeper exploratory well in the area. As another priority target for oil and gas exploration, a potential zone of Vendian clastic deposits wedging on the southwestern slope of the Suntar uplift has been identified. A forecast has been made for the distribution of lithological traps stacked with well-sorted granular Vendian reservoirs in the northern parts of the Ergedzheysky and Ulugursky license areas. In the allochthonous part of the section, the potential for oil and gas content in carbonate deposits from the Vendian and Lower Cambrian periods is highlighted in reservoirs formed by secondary processes. It is assumed that thrust deformations could lead to the circulation of aggressive solutions, resulting in the formation of secondary fractured cavernous reservoirs. Subsequently, hydrocarbon accumulations may migrate and accumulate within these reservoirs. Good gas prospects were also noted in the upper part of the section, where gas deposits were confirmed in newly discovered fields. The results of direct geochemical testing of the Ulugur and Ergedzheysky license areas are presented, enabling the preliminary delineation of promising zones and areas in the studied territory. At the same time, narrow elongated geochemical anomalies are associated with the prospects of the allochthonous part of the section, while isometric anomalies are linked to the autochthonous part of the section. The need to consolidate all available geological and geophysical information on the Pre-Atomic deflection within the framework of case studies is noted.

Interaction between shallow and deep structures: Forward-modeling kinematics sequence of a fold-and-thrust belt with double detachment

It is crucial to determine the sequence of deformation and the interaction between shallow and deep structures within the multiple detachment systems to comprehend geological processes fully in fold-and-thrust belts (FTBs). Here, we implement forward modeling to investigate the geometric, kinematic, and syntectonic sedimentary characteristics of shallow and deep structural interactions. We design four combinative patterns of geometric structures, three kinematic sequence scenarios, and two settings with different ratios of the sedimentation rate to the uplift rate to examine the influence of such settings on growth strata geometry. The most effective results of 24 groups of shallow and deep structural interactions were obtained for various combinations of fault-bend fold, detachment fold, and tectonic wedge. This study provides a sequential kinematic image of FTBs, illustrating the interaction of two sets of detachments and demonstrating how different styles of pre- and growth strata can be utilized to identify shallow and deep structure deformation processes. The geometry of pre- and growth strata observed in the models is similar to that observed in natural structures. These forward models facilitate a better understanding of the complex geometry and kinematics of the interaction between shallow and deep fault-related folds.

Middle Miocene renewed subduction of arabian-eurasian plates: Implications for convergent tectonic mechanisms, tectonically-induced fluid overpressures, and sediment recycling dynamics

The complex interplay between thrust wedge deformation, tectonically-induced fluid overpressures, and the complex phases of wedge-top sedimentary depositional systems in active plate convergent margins presents a formidable challenge. The offshore Makran accretionary wedge (MAW) is the world's largest, formed by the convergence of Arabian plate underneath Eurasian plate in the Early Cretaceous, followed by Middle Miocene renewed subduction. In this research, geological and geophysical constraints derived from seismic and borehole stratigraphy, seismic attributes, depth structural maps, isopach maps and 3D structural geological models reveal that Middle Miocene renewed subduction controls thrust wedge deformation. Additionally, it influences deep fluid overpressure and the deformational pattern of wedge-top sedimentary depositional systems. The seismic data analysis suggested that the basement pre-kinematic Himalayan turbidities depositional system (HTDs) have been tectonically incorporated into the accretionary wedge by Middle Miocene renewed subduction, which gave rise to complex folding and N-dipping imbricate thrusting features. These N-dipping imbricate thrust faults initiated sediment underplating and served as major structural pathways for deep fluid overpressure migration, resulting in the formation of fluid escape pipes. The fluid escape pipes exhibit conical and bifurcating geometries with inclination angles of approximately 73°, 90°, and 100°, signifying the upward migration of deep overpressured fluids. Furthermore, the Middle Miocene to Pliocene syn-kinematic piggyback and growth depositional system (PGDs) show progressive thickening (Max ∼3600 m) towards onshore MAW. It lies unconformable above the pre-kinematic HTDs and carries valuable sedimentation records, growth stratal patterns, onlap terminations, and truncations against growing structures, revealed the timing and spatial deformation of thrust faults in 3D space. In contrast, the Pleistocene to Recent post-kinematic progradational depositional system (PDs) exhibits clinoforms marked by top-lapping, on-lapping, and down-lapping reflection, which are primarily controlled by sediment recycling dynamics and sea level change since Pleistocene. It shows progressive thickening (Max ∼1800m) towards the Makran subduction zone and lies unconformably above the syn-kinematic PGDs. Abridging the analyses, the tectonic reconstruction and deformation mechanisms model shows four phases, e.g. (1) initiation of subduction and accretionary wedge formation in Eocene, (2) N-dipping imbricate thrust faults and deep fluid overpressure triggered by Middle Miocene renewed subduction, (3) development of piggyback basins and growth stratal geometries in Middle Miocene to Pliocene, (4) thrust deformation ceases and development of progradational depositional system.

Study on thermal deformation of high-pressure aerostatic thrust bearing in uneven temperature field

Study on thermal deformation of high-pressure aerostatic thrust bearing in uneven temperature field

Lubrication characteristics and thermal deformation of hydrostatic thrust bearing based on conjugate heat transfer

PurposeThe purpose of this paper is to analyze the variation of temperature field, pressure field and deformation of hydrostatic thrust bearing under different working conditions, so as to provide a theoretical basis for improving accuracy and reliability.Design/methodology/approachIn this study, the double rectangular hydrostatic bearing of type Q1-224 was selected as the research object, and the simulation was carried out according to different working conditions, and the obtained data were summarized regularly.FindingsIt is found that the overall temperature of hydrostatic bearing increases with the increase of speed and load, and the increase in load will result in a larger pressure distribution which first increases and then decreases with the speed. The deformation trend of the deformation field is found, and it is found that the force deformation is larger than the thermal deformation at low rotational speed, and the thermal deformation is larger than the force deformation at high rotational speed.Originality/valueIn this study, the fluid-structure coupling method of conjugate heat transfer is applied to study the whole hydrostatic bearing. Most of the previous studies only studied the oil film and considered the influence of the convective heat transfer between the hydrostatic bearing and the air in heat transfer, which is rarely seen in the previous research literature.

Fluid inclusions in vein quartz as a reflection of the deformation stages of the junction area of Baikal-Muisk and Barguzin-Vitim structural-formation zones (Western Transbaikalia)

Research subject. Fluid inclusions in quartz of three vein systems associated with tectonic cracks occurred during the development of thrust and shear deformations of the Western Transbaikalia. Vein systems localized in volcanic, terrigenous and granite rocks. Methods. The composition of fluid inclusions was studied by microthermometry, Raman spectroscopy and gas chromatography-mass spectrometry. Results. The quartz under study was formed by high-density medium-temperature NaCl-KCl and a low- and medium-salinity water-carbon dioxide fluid (2-5 wt % NaCl eq.). A distinctive feature of quartz of different vein systems was found to be the gas phase composition of inclusions associated with the composition of host rocks. The minimum temperatures of vein quartz formation were determined to range from 180 to 450°C under the minimum fluid pressure values of 0.7-2.9 kbar. Conclusions. Complex vein systems of the junction zone of the Baikal-Muiskaya and Barguzino-Vitimskay SFZ, confined to different host rocks and having different structural positions, are characterized by a similar fluid composition and a common thermodynamic history reflecting the change of deformation aggregates. The metamorphogenic-hydrothermal nature of the fluid involved in the formation of quartz vein systems was established. The development of the hydrothermal system was accompanied by its influence on the host rocks, which was manifested in the variations of fluid composition. The evolution of a single hydrothermal system is associated with tectonic deformation processes, which can be described by three dynamic stages corresponding to three quartz generations.

Tectonic Deformation of an Intraplate Orogenic Belt: Mesozoic Sedimentary Basins in the Northeastern Qilian Shan, China

The Qilian Shan, located in the northeastern Tibetan Plateau, is an intraplate orogenic belt that underwent several episodes of fold and thrust deformation, particularly during the Mesozoic and Cenozoic. However, the deformation styles and relationships between the basin and mountains remain controversial. Therefore, in the current study, we conducted detailed field mapping of the sedimentary basins in Sunan and Huangcheng, and observed three episodes of compressive tectonic activity. We also restored a deformed section to determine the shortening rate of the Cretaceous sedimentary Sunan Basin. The first thrust episode, during the Paleogene, involved a southwestward thrust motion, comprising the Yumu Shan and Gaizhangdaban thrust systems. The second Neogene episode involved the northeastern thrust belt in the northern Qilian Shan, which comprises the Northern Qilian thrust system. The third episode produced NW-trending strike-slip activity that became the major tectonic deformation style; thus, the entire block rotated clockwise. Additionally, the restored section revealed that the Cretaceous strata have been shortened by ∼3.56%. Collectively, these results indicate that the Sunan and Huangcheng area on the northeastern Tibetan Plateau is influenced by the far-field effects of the collision between the Indian and Asian continents, as well as the effects of intraplate orogenic processes related to the collision of the Alashan Block and the Qilian Shan. Therefore, the current study has defined the deformation style in the northeastern Qilian Shan region, so we wish to give a clarification of the tectonic evolution and forecast the tectonic propagation in the Qilian Shan region.

Zircon (U-Th)/(He-Pb) double-dating constraints on the interplay between thrust deformation and foreland basin architecture, Sevier foreland basin, Utah

AbstractThe Cretaceous Cordilleran foreland basin strata exposed in the Book Cliffs of eastern Utah and western Colorado have motivated important concepts linking thrust belt deformation and foreland basin evolution largely on the basis of sequence stratigraphy, stratal architecture, and sediment provenance evolution. However, these methods and approaches generally cannot provide critical insights into the temporal or causal linkages between foreland basin architecture and thrust belt deformation. This is in part due to discrepancies in age resolution and lack of evidence with which to directly couple sediment supply and basin-fill evolution to thrust belt unroofing. New detrital zircon (DZ) geothermochronometric data from Upper Cretaceous proximal to distal foreland basin strata in the Book Cliffs provide new quantitative insights into sediment origin and dispersal in relation to thrust belt deformation and exhumation. Detailed DZ U-Pb and (U-Th)/He double dating reveals that the Book Cliffs foredeep detritus was mainly delivered by transverse routing systems from two major sources: (1) Neoproterozoic and Lower Paleozoic strata from the central Utah Sevier thrust belt, and (2) Permian–Jurassic and synorogenic Cretaceous strata recycled from the frontal part of the thrust belt. A dramatic increase in Sierran magmatic arc and Yavapai-Mazatzal DZ U-Pb ages, as well as Paleozoic DZ He ages, in the deeper marine portions of the foreland basin points to axial fluvial and littoral sediment input from the Sierran magmatic arc and Mogollon highland sources. Both transverse and axial transport systems acted contemporaneously during eastward propagation of the Late Cretaceous thrust belt. DZ He depositional lag time estimates reveal three distinct exhumation pulses in the Sevier thrust belt in the Cenomanian and Campanian. The exhumation pulses correlate with shifts in sediment provenance, dispersal style, and progradation rates in the foreland basin. These new data support conceptual models that temporally and causally link accelerated exhumation and unroofing in the thrust belt to increases in sediment supply and rapid clastic progradation in the foreland basin.

Ca. 835–823 Ma doming extensional tectonics in the west Jiangnan accretionary orogenic belt, South China: Implication for a slab roll-back event

The Neoproterozoic Jiangnan accretionary orogenic belt recorded the accretion and collision of the Yangtze and Cathaysia blocks to form a stablized South China Block, but related geometry and kinematics is poorly constrained, leading to largely varied tectonic models. Here, we present detailed field investigation and kinematic analysis of the plutonic-metamorphic complexes in the Yuanbaoshan and Sanfang areas of the west Jiangnan orogenic belt, which enables identification of extensional granite-cored domes. In the dome margins, down-dipping lineations display a radial pattern and dome dominated foliations are extensively developed. The shearing structures within the plutonic-metamorphic complexes display extensional shearing surrounding the Yuanbaoshan and Sanfang granitic dome cores. Gneissic granites and massive ones from both the Yuanbaoshan and Sanfang plutons yield comparable crystallization ages of ca. 835–823 Ma that are within age errors of each other, as are the sheared recrystallized asymmetric quartz veins and mylonites dated at 831 Ma. Overall ages of the deformed Sibao Group and the undeformed overlying Danzhou Group, along with those of the granite plutons and mylonites, suggest formation of the granite-cored domes at ca. 835–823 Ma, coeval to the timing of emplacement of the granitic plutons. Locally, top-to-the-E thrusting structures are also observed in the west Yuanbaoshan and Sanfang areas and are inferred as at ca. 860–835 Ma, coinciding well with E- or SE- directed structures developed elsewhere in the Jiangnan orogenic belt, but in contrast with doming extensional shearing structures. Therefore, overall geometry and kinematics in the west Jiangnan belt indicate development of granitic dome related extensional ductile shearing deformation dated at ca. 835–823 Ma and a possible top-to-the-E compressional ductile thrusting deformation within 860–835 Ma. Given the previously inferred regional geology observations, along with age and chemical data across the Jiangnan orogenic belt, the dominant extensional shearing deformation in the region argue for a slab roll-back event within an accretionary belt, typical of domes-and-basins structures formed in accretionary convergent continental margin. The top-to-the-E thrusting is here interpreted as corresponding to compressional regime generated by the west directed subduction of oceanic crust beneath the northern Guangxi continental margin arc in the west Jiangnan orogenic belt.

Deformation, Magmatism, and Sulfide Mineralization in the Archean Golden Mile Fault Zone, Kalgoorlie Gold Camp, Western Australia

AbstractThe Golden Mile fault zone is a key controlling structure to the estimated 75 Moz gold endowment of the Kalgoorlie gold camp in the Yilgarn craton of Western Australia. The earliest structures in the fault are F1 folds that developed during D1 recumbent-fold and thrust deformation (<2685 ± 4 Ma). These F1 folds are overprinted by a pervasive NW- to NNW-striking S2 cleavage related to sinistral shearing beginning with 2680 ± 3 Ma D2a sinistral strike-slip and culminating with ca. 2660 Ma D2c sinistral-reverse movement. The majority of deformation in the fault zone correlates to ca. 2675 Ma D2b deformation, which is characterized by sinistral-normal kinematic indicators. Late, ca. 2650–2640 Ma D3 dextral-reverse kinematic indicators overprint the earlier D2 structures. Pyrrhotite-chalcopyrite-pyrite-sphalerite-galena assemblages were emplaced throughout the D2 event within NE-trending D2a tensile fractures, NW- to NNW-striking D2b normal faults and associated breccias, and NW- to NNW-striking D2c low-angle veins, with the latter D2b and D2c structures correlating to the Fimiston and Oroya mineralization types, respectively. All D2a-, D2b-, and D2c-related sulfides in the Golden Mile fault zone show similarly restricted δ34S (~1.0–4.5‰) and elevated Δ33S (~2.0–3.0‰) values that reflect strong local sulfur contribution from shales of the Lower Black Flag Group and host-rock buffering of hydrothermal fluids related to the Fimiston and Oroya mineralization events. This host-rock buffering decreased fluid fO2, favoring the development of pyrrhotite-pyrite stable sulfide assemblages and causing respective decreases and increases in fluid Au-Te and Pb-Bi-Sb concentrations. At the camp scale, the Golden Mile fault zone exerted a primary control on the distribution of porphyry dikes and gold deposits; however, magma and hydrothermal fluid circulation was favored in adjacent, higher-order structural sites due to the fault zone’s incompetent rheology and tendency for ductile deformation and diffuse fluid flow. Other Archean examples such as Au deposits of the Larder Lake-Cadillac deformation zone in the Superior craton illustrate that this type of diffuse fluid flow in large-scale crustal fault zones can result in disseminated economic mineralization. However, this study highlights that host-rock effects on fluid chemistry in large-scale crustal fault zones exercises a strong control on a fluid’s propensity to form ore. The results of this study emphasize that both the rheology and chemistry of rocks within and adjacent to large-scale deformation zones act as important controls on the formation of gold ore in Archean terranes.

Alkaline granitic magmatism of the Western Transbaikalia: Petrogenetic and geodynamic implications from U-Pb isotopic–geochronological data

The Mongolian–Transbaikalian volcanoplutonic belt extends for almost 2000 km through northern Mongolia and Transbaikalia and hosts several hundreds of plutons of alkali feldspar syenites (AFS) and peralkaline granites (PA) that formed at 280–270 and 230–210 Ma. The giant (~220 km2 in area) Sherbakhta pluton in the Vitim plateau (western Transbaikalia) is located and composed of metaluminous (A/CNK ≤1), high ferroan AFS syenites (10.7–12.3 wt% Na2O + K2O; NK/A < 1) and A-type peralkaline granites (8.7–9.5 wt% Na2O + K2O; NK/A 0.95–1.05). The U-Pb (SHRIMP-RG, LA-ICP-MS) age of the pluton is 260 Ma. The isotope and geochemical characteristics of the studied pluton (ɛNd(T) –2.4 to −2.9; TNd(DM-2) 1.25–1.27 Ga; ɛHf(T) 1.1–0.6, THf(DM-2) 1.02–1.05 Ga, δ18О of quartz 7.3–8.22‰) indicate that the parental trachytic–trachyandesitic melt is compositionally similar to high-Sr syenites of the Sherbakhta pluton and derived by the melting of the mafic, moderately potassium-rich lower crustal source. The magmatic evolution of the parental melt toward a residual ferroan peralkaline granitic melt in the intermediate chamber was controlled by fractional crystallization of sodic plagioclase and K-feldspar, followed by amphibole and aegirine under low oxygen fugacity. The A-type granitoids in the Transbaikalia region formed in the intracontinental geodynamic setting, probably as a result of impact of the mantle plume on heated plastic crust of a young orogen, which formed during the Late Hercynian fold thrust deformations.

The investigations of the deformation of the Great Counter Thrust (GCT) in Zedang area, South Tibet: A case study of magnetic fabric and EBSD analysis

仁布-泽当逆冲断层是喜马拉雅大反向逆冲断层（GCT）在藏南地区的重要延伸部分，也是喜马拉雅造山带北部边界新生代最为活动的构造单元之一。新生代以来特提斯喜马拉雅的构造变形组构特征的研究对于深入理解碰撞造山带演化与高原隆升具有重要构造意义。本文综合GCT泽当-琼结段断层的宏观与微观变形特征，对断裂带石英脉、围岩中石英和云母矿物的电子背散射（EBSD）组构及断层两侧岩石磁组构（AMS）特征进行对比分析。结果表明对AMS主要贡献来自顺磁性云母、绿泥石等，磁化率各向异性椭球体以压扁状为主，磁面理与构造面理（劈理、断层面）基本重合，显示较强的构造变形磁组构特征；磁线理优选方向近南北向，且与观测北向逆冲断层方向一致，揭示剪切作用在变形过程中的持续作用。研究发现泽当地区GCT附近石英微观结构从围岩至断层区，石英至少呈现3种不同类型的微观变形机制：围岩区溶解蠕变、断裂带石英以膨凸重结晶和亚颗粒旋转重结晶作用为主。断裂带石英的c轴EBSD组构指示变形为低温（300~400℃）环境，其中黑云母的结晶学优选（CPO）与磁组构主轴优选方向存在高度的一致性，进一步证实了顺磁性矿物黑云母对AMS的主要贡献。综合研究表明泽当地区GCT的韧性变形是断层处在中上地壳韧性带的活动阶段变形的结果，也代表了特提斯喜马拉雅在碰撞、高原隆升期的变形主要特征。;Renbu-Zedang thrust fault is one of the most important parts of the Great Counter Thrust (GCT) in South Tibet, as well as one of the most active faults of the Himalaya Orogeny in Cenozoic. The investigation of the deformed fabric has great importance for deep understanding of the orogen evolution and plateau uplift. In this paper, we combined the mesoscopic and micro-structures of the fault rocks, especially, the comparison analysis of the Electron Backscattered Diffraction (EBSD) fabrics of quartz, mica and the anisotropy of magnetic susceptibility (AMS) of samples around the fault zone. The AMS results suggest an oblate magnetic ellipsoid predominant at most sample sites, and magnetic foliations nearly coincide with the tectonic foliations (cleavage or fault plane), both of which suggest strong tectonic fabric dominant of the area. S-N directed magnetic lineation in line with the fault moving direction indicated the continuing thrusting happened in the fault zone. Quartz microstructure suggests that this fault zone at least underwent three different levels of deformation mechanism, namely, the dissolution creep static recrystallization (quartz grains shows polygon seams), the bulging (BLG) recrystallization and the subgrain rotation (SGR) recrystallization, respectively. Low deformation temperature (300~400℃) is suggested from the c-axes of quartz EBSD fabric. The Crystallographic Preferred Orientation (CPO) of biotite shows strong correspondence with the magnetic fabrics which further confirmed the dominance of paramagnetic to the AMS. The ductile deformation of GCT in the Zedang area is the result of the fault in ductile zone of the middle and upper crust uplift movement stage, also represent the plateau uplift and deformation of the Tethyan Himalayan since Cenozoic.

Thermohydrodynamic performance of water-lubricated thrust bearing of mine high speed rescue pump

In order to meet the requirement of axial force balance of mine rescue pump with high speed and big power, the capacity and reliability of water-lubricated thrust bearing of the pump unit should be improved. This paper presented a study on the capacity of water film and bearing bush deformation of water-lubricated thrust bearing based on the change of temperature in the motor chamber, which is under the actual operation condition of mine high speed rescue pump. In this study, the Reynolds equation was solved by MATLAB to get the thickness of water film, and the deformation of bearing bush was obtained through the joint solution of heat-fluid-solid coupling equation by ANSYS. The results show that the temperatures have little effect on the pressure distribution of water film and the deformation distribution of bearing bush. However, the maximum pressure of water film increases with the temperature. The research of the paper could provide theoretical support and technical guidance for the design of water-lubricated thrust bearings under big power and high speed conditions in the future.

Fold–Thrust Deformations of New Siberia Island (Novosibirsky Islands, Russia): Age, Morphology, and Genesis of Structures

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

Late Cretaceous-Paleocene stratigraphic and structural evolution of the central Mexican fold and thrust belt, from detrital zircon (U-Th)/(He-Pb) ages

Combined U-Pb and (U-Th)/He ages on a small sample set of Cretaceous foreland-basin sandstone from a transect of the fold-thrust belt in east-central Mexico reveal correspondence between episodes of thrust-belt exhumation with previously postulated deformational events and with at least one wedge of synorogenic sediment in the adjacent Tampico-Misantla basin. Detrital zircon U-Pb ages, sandstone petrography and multidimensional scaling analysis of the Cenomanian-Turonian Mineral de Pozos sandstone, the Coniacian Soyatal and Campanian San Felipe formations, and the Paleocene Chicontepec Formation indicate sediment sources in the Mexican Cordilleran magmatic arc of western Mexico, the accreted Guerrero arc terrane, and Mesozoic sedimentary rocks of central and western Mexico. (U-Th)/He cooling ages define into three age clusters: (1) ~136-120 Ma, (2) ~99-80 Ma, and (3) ~66-56 Ma. Cooling ages are younger toward the transect's western part, which represents the interior part of the fold-thrust belt. Dominant Early Cretaceous cooling ages in the San Felipe Formation indicate lack of, or partial, resetting of the He system. Late Cretaceous cooling ages are dominant in the Soyatal Formation and are partially equivalent to their maximum depositional age (88 ± 1 Ma), suggesting derivation of grains from adjacent rapidly exhumed thrust sheets. Alternatively, these grains were partial reset. Youngest cooling ages dominate the Mineral de Pozos sandstone samples, indicating Paleocene exhumation and erosion of interior thrust sheets. The Paleocene exhumation event is equivalent to stratal ages of the lower part of the Chicontepec Formation, and sandstone composition of that unit indicates dominant sediment sources in carbonate rocks of the frontal part of the fold-thrust belt. Combined cooling ages and sandstone petrography thus indicate coeval exhumation of the entire width of the orogen in the Paleogene, rather than out-of-sequence thrust-sheet uplift and exhumation of only the interior part of the thrust wedge. Orogen-wide exhumation is corroborated by a previously published early Paleocene illite 40Ar/39Ar age of 64 ± 2 Ma for thrust deformation at the eastern flank of the Valles-San Luis Potosí carbonate platform, which formed the latest Cretaceous-Paleocene boundary between the fold-thrust belt and foreland basin in which the Chicontepec Formation was deposited.

Late Carboniferous (Kasimovian) closure of the South Tianshan Ocean: No Triassic subduction

The proposed Triassic age of oceanic subduction and high-pressure/low-temperature (HP-LT) metamorphism in the South Tianshan orogen (STS) of the southwestern Central Asian Orogenic Belt needs to be re-examined on the basis of field relationship and precise age dating. Our biostratigraphic study in the Atbashi Range of southern Kyrgyzstan indicates that sedimentary strata unconformably overlie the HP-LT metamorphic rocks within the Turkestan suture zone and have a late Kasimovian (ca. 305 Ma) age. This constrains the minimum age of eclogite metamorphism in the HP-LT metamorphic complex. A Late Pennsylvanian to early Permian (Asselian) hinterland basin overlaps the margins of the Middle and South Tianshan and the ophiolitic suture between them, thus leaving no space for an oceanic basin in the northern STS in the late Permian or Triassic. In the south, overlap assemblages stitching the STS with the Tarim Craton consist of late Asselian to early Sakmarian limestones and early Permian rhyolites. Early Permian (ca. 295–265 Ma) post-collisional A-type granites and sub-alkaline plutons are widespread in the STS and are not affected by thrust deformation. These facts indicate that thrust packages of the STS were stacked together and welded to the margin of the Tarim Craton by the early Permian. The widespread occurrence of early Permian sub-alkaline granites is also not compatible with an oceanic accretionary wedge setting in the STS during the Permian or Triassic.Permian and Triassic zircon ages for subduction-related HP-LT metamorphic rocks and ophiolitic gabbro from the Atbashi and Djandjir ranges reported in two recent papers contradict geological relationships. A review of reported analytical data shows that anomalously young ages in all studied samples are based on geologically meaningless single zircon analyses and/or discordant data, which cannot be used for age calculation. The suggestion that an oceanic basin in the STS remained open and subduction continued until the Middle Triassic is erroneous because of insufficient consideration of basic regional geological relationships and incorrect interpretations of analytical results.

Horizontally deplacement geomasses in the continental rift geostruсtures (on the example of the Dnipro-Donets paleorift). Part 2. Structural parageneses of the reid deformation of the sedimentary cover

Formulation of the problem. The inversion stages of the structural-material evolution of the continental crust are characterized by regional scale of the deformation of volume tectonic flow of platform sedimentary rocks, which caused significant horizontally-healthy movements of tectonically activated geo-mass in the intra-plate graben-rift. The dynamic deformation of geomases manifests itself at the final stages of the geological development of such structures; therefore, it determines the main features of the systemic organization of the modern architecture of the basement and sedimentary cover complexes. Review of previous publications and studies. Secondary deformation linear slope, according to Patalakha E. (1979); Alekseev V. (1990) is considered as a set of local strike-slip zones, formed on spherically-located viscous faults, forming joint tectonic flows. The structural skeleton of tectonic flows, as the basis of the tectonic dislocation process, make offsets with the horizontally and rotational component movements. Horizontal landslides are typical disjunctive elements of the continental structures formed in the geodynamic conditions of the transtension (grabens, rifts), transpression (folded mobile belts, intra-plate activation zones), as well as the basic structural elements of the strike-slip tectonics of the sedimentary basin. The purpose of the article. The second part of the trilogy continues regional geotectonic studies of post-rift complications of the sedimentary cover structure of Dnipro-Donets Paleorift (DDP), covering the three main stages of the platform tectonic activation. Late Hercynian epoch was characterized by the formation of large linear anticlinal zones and salt-shafts against the background of the general syneclizal deflection of sedimentary basin, located within the paleorift. Cimmerian epoch of tectonic activity led to significant thrust deformations of the primary structural forms of the cover in the geodynamic setting of collision compression with intensification of the horizons of the sedimentary cover. The structural manifestation of strike-slip tectonics at Alpine epoch in sedimentary complexes are mainly horizontal displacements of geomases of blocks, lineaments, local tectonic elements and structures along dynamically interconnected coulisse of strike-slip domains. Methods. Structural kinematic analysis of transformations of the fracture systems of the Upper-Visean sedimentary complex under the influence of natural mechanism of reid tectonic flow of rocks. Results. The secondary structures of strike-slip deformation, structural kinematic parageneses, dislocations zones and subregional structural waves were identified in the structure of the platform cover, which are natural geological objects formed at the inversion stages of geological development of DDP. Scientific novelty and practical significance. The result of structural manifestation of volume tectonic flow in the platform complex was horizontal displacements of the original tectonic elements, blocks, segments, structures along dynamically-linked strike-slip domains. This is caused by the formation of secondary deformation structures of various scales, morphology and genesis, which comprise longitudinal structural waves of strips of post-rift deformations in the structure of the sedimentary cover of DDP.

Late Cenozoic Foreland‐to‐Hinterland Low‐Temperature Exhumation History of the Kashmir Himalaya

AbstractNew apatite and zircon (U‐Th)/He cooling ages quantify late Cenozoic exhumation patterns associated with fault activity across the Kashmir Himalaya. Apatite (U‐Th)/He (AHe) cooling ages of detrital grains from the Sub‐Himalayan foreland sediments indicate significant resetting. AHe data and thermal modeling reveal cooling and exhumation initiated by 4 Ma at the deformation front and by 2–4 Ma throughout other Sub‐Himalayan structures. Exhumation rates for Sub‐Himalayan structures are ≥1 mm/year. In the hinterland, thrust sheet samples from the Main Boundary thrust and Main Central thrust yield AHe cooling ages between 5.1 and 21.1 Ma. Published apatite fission track cooling ages (&lt;3 Ma) and high exhumation rates (3.6–3.2 mm/year) across the Kishtwar window further to the north are consistent with AHe data from the Sub‐Himalayan structures. The pattern of cooling ages and rates indicates that exhumation occurs in association with changes in the Himalayan basal décollement ramp geometry. Hinterland zircon (U‐Th)/He (ZHe) data show a pronounced abundance and probability spike in cooling ages between 14 and 21 Ma, a period when Main Central thrust motion is well documented throughout the Himalaya. ZHe single‐grain ages from Sub‐Himalayan samples contain a nearly identical cluster from 16 to 23 Ma. Cooling patterns across the Kashmir Himalayas do not correlate spatially with modern monsoon precipitation, suggesting that climate‐related precipitation and exhumation are decoupled. Coeval translation over the basal décollement and distributed imbricate thrust deformation of the foreland in the upper plate characterizes fault‐related exhumation of the Sub‐Himalayan orogenic belt after 4 Ma.

Плюмы - новое слово в геологии Урала

Subject. The ideas of plume tectonics became active and developing only several years later than the theory of plate tectonics. But in the Urals, the question of plume tectonics, contrary to plate tectonics, was not raised, with rare exceptions, until the latest decade. It is explained by great difficulties in revelation of plumes in any ancient foldbelt, because seismic tomography is not applicable, and magmatic complexes are partly covered by younger sediments, partly eroded, and, additionally, undergone distortion, connected with continental break-ups and drift, subduction and fold-and thrust deformations. Materials and methods. However in recent years, among the magmatic complexes of the Urals (mostly in its western areas), Pay-Khoy and Novaya Zemlya, thanks to precise definition of magmatic formations ages, study of their geodynamically conditioned petrochemistry and their correlation with other regions, the author identified ten levels of probable manifestations of plume/superplume events. Results. It is assumed that in the modern Urals the relics of the following plumes: Navysh (Lower Riphean), Mashak (Middle Riphean), Arsha and Kiryabinka (Terminal Riphean), Mankhambo (Cambrian), Kidryas (Lower-Middle Ordovician, Ushat (Late Ordovician-Lower Silurian), Kola-Dniepr (Devonian), Stepninsk (Permian), Ural-Siberian (Lower-Middle Triassic) had remained.

Structural characteristics and evolution of the South Yellow Sea Basin since Indosinian

Based on the seismic data gathered in past years and the correlation between the sea and land areas of the Lower Yangtze Platform, the structural characteristics of the South Yellow Sea Basin since the Indosinian tectonic movement is studied in this paper. Three stages of structural deformation can be distinguished in the South Yellow Sea Basin since the Indosinian. The first stage, Late Indosinian to Early Yanshanian, was dominated by foreland deformation including both the uplifting and subsidence stages under an intensively compressional environment. The second stage, which is called the Huangqiao Event in the middle Yanshanian, was a change for stress fields from compression to extension. While in the third stage (the Sanduo Event) in the Late Himalayan, the basin developed a depression in the Neogene-Quaternary after rifting in the Late Cretaceous-Paleogene. The long-time evolution controlled 3 basin formation stages from a foreland basin, then a fault basin to a final depression basin. In conclusion, since the Indosinian, the South Yellow Sea Basin has experienced compressional fold and thrust, collisional orogen, compressional and tensional pulsation, strike-slip, extensional fault block and inversion structures, compression and convergence. The NE, NEE, nearly EW and NW trending structures developed in the basin. From west to east, the structural trend changed from NEE to near EW to NW. While from north to south, they changed from NEE to near EW with a strong-weak-strong zoning sequence. Vertically, the marine and terrestrial facies basins show a “seesaw” pattern with fold and thrust in the early stages, which is strong in the north and weak in the south and an extensional fault in later stages, which is strong in the north and weak in the south. In the marine facies basin, thrust deformation is more prevailing in the upper structural layer than that in the lower layer. The tectonic mechanism in the South Yellow Sea Basin is mainly affected by the collision between the Yangtze and North China Block, while the stress environment of large-scale strike-slip faults was owing to subduction of the Paleo-Pacific plate. The southern part of the Laoshan uplift is a weak deformation zone as well as a stress release zone, and the Meso-Paleozoic had been weakly reformed in later stages. The southern part of the Laoshan uplift is believed, therefore, to be a promising area for oil and gas exploration.