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Zircon U-Pb age, geochemical characteristics, and tectonic implications of the Early Permian ultrabasic dykes in the Harlik Mountain,East Tianshan, Xinjiang
, Available online  , doi: 10.12090/j.issn.1006-6616.2024020
Abstract (18)
Abstract:
[ Objective ]During multiple stages of magmatic activity in the Halrick Mountains of the East Tianshan, extensive granitic and mafic dyke swarms were formed.To limit the closure time of the ancient Asian Ocean in this area and to elucidate the tectonic environment in which ultrabasic rock walls were formed. [ Methods ]This study reports on the petrography, geochemistry, and zircon U-Pb ages of a particular type of ultrabasic dyke swarm (amphibolites) in Qincheng, Hami.[ Results ] The results show that the amphibolites have SiO2 contents ranging from 39.00% to 45.48%, TiO2 contents ranging from 1.60% to 3.01%, and Mg# values ranging from 50 to 60, They are relatively weakly enriched in light rare earth elements ((La/Yb)N = 1.34~2.25) and show no Eu anomalies (δEu = 0.76~1.12). They are enriched in large ion lithophile elements (LILEs: Rb, Ba, K, Sr) and depleted in high field strength elements (HFSEs: Nb, Zr, Hf). The amphibolites belong to the alkaline series rocks. The LA-MC-ICPMS zircon U-Pb ages reveal that these three amphibolites crystallized at 298.4±1.7 Ma, 297.7±1.6 Ma, and 295.5±1.6 Ma, respectively. The whole-rock Sr-Nd compositions indicate initial 87Sr/86Sr ratios ranging from 0.7047 to 0.7051 and εNd(t) values ranging from -2.63 to 1.81. [ Conclusion ]Based on comprehensive analysis of regional geology, chronology, geochemistry, and Sr-Nd isotopes, it is suggested that the primitive magma of the Early Permian amphibolites in Qincheng possibly originated from partial melting of the lithospheric mantle and these rocks were formed in a post-collisional extensional tectonic setting.At the same time, it implies that the ancient Asian Ocean in the Harlik Mountains region closed before the Early Permian.
Exploration and scientific research of Jiaojia-type gold deposit
, Available online  , doi: 10.12090/j.issn.1006-6616.2024061
Abstract (11) PDF (12940KB)(9)
Abstract:
Jiaojia-type gold deposit that discovered by Shandong geologists in the northwest Jiaodong Peninsula in the 1960s is a new type of gold deposit. It has gone through twelve years of exploration and scientific research from discovery to establishment. The new type of gold deposit has been rapidly promoted after its establishment, and has achieved fruitful prospecting results in China. The deep exploration achievements of Jiaojia-type gold deposit constantly spring up in Jiaodong area since the 21st century. The accumulated gold resource reserves submitted have been 3, 617.12 tons by 2020, which has helped Jiaodong area become the third largest gold cluster in the world, and China's gold reserves have risen to the second place in the world. While continuous breakthroughs have been made in the deep exploration of Jiaojia-type gold deposits, great progress has also been made in the scientific research. For example, the metallogenic age of gold deposits has been precisely defined, major breakthroughs have been made in the research of metallogenic dynamics background, the understanding of the source and evolution of ore-forming materials has been more in-depth and refined, and the metallogenic model has been more perfect. The research of metallogenic depth and prediction also shows that the Jiaojia-type gold deposit has great potential for deep prospecting. These research works enriched the metallogenic theory of Jiaojia-type gold deposit, make the metallogenic prediction results more accurate and reliable, and effectively guide the gold exploration in the Jiaodong Peninsula.
A review of the formation law and catastrophic evolution mechanism of giant landslides in complex engineering geological conditions in the western alpine valley area, China
, Available online  , doi: 10.12090/j.issn.1006-6616.2024031
Abstract (40) PDF (2183KB)(13)
Abstract:
[Objective] Most hydroelectric projects in Western China are situated in alpine canyons. The intricate engineering geological conditions in this area contribute to the widespread distribution of landslide disasters on the reservoir banks of hydroelectric projects. [Methods] Based on the engineering geological characteristics of the western alpine canyons, the correlation between topography, geological structure, landslide material, slope structure, hydrogeological conditions, and the formation and progression of landslides is analyzed. It also delineates the types and features of landslide development in the western region and the mechanical mechanisms governing the evolution of typical landslide disasters. [Results] The results indicate that the landslides are characterized with slopes ranging from 30° to 50°, elevations exceeding 1000 m, and volumes surpassing one million cubic meters. Triassic, Ordovician, and Silurian strata are identified as the principal slippery strata in this area. Rainfall and reservoir impoundment significantly influence landslide stability, leading to erosion datum uplift and range expansion. Fluctuations in water levels result in diminished rock and soil properties along the leading edge of advancing landslides. [Conclusion] The most frequent landslides in the western alpine region include accumulation landslides dominated by traction, thrust, and composite mechanisms, as well as rock landslides dominated by bedding, buckling, anti-dip, and seating mechanisms. [Significance] The study elucidates landslide disaster mechanisms under varying evolutionary and failure mechanical processes, providing a significant guidance value for the identification, monitoring, early warning and prevention of landslide disasters in the western region.
Prevention and control of land subsidence and earth fissures in Suzhou–Wuxi–Changzhou region
, Available online  , doi: 10.12090/j.issn.1006-6616.2024051
Abstract (47) PDF (5881KB)(20)
Abstract:
Abstract: [ Objective] The Suzhou–Wuxi–Changzhou region is one of the most severely affected areas by land subsidence, both in China and globally. In the early 1970s, land subsidence occurred and resulted in the formation of ground fissures caused by differential subsidence, thus resulting in significant economic losses. In this century, the rate of ground subsidence has decreased, with some areas experiencing regional ground resilience. The unique developmental history of ground subsidence allows one to comprehensively interpret its evolutionary process and causal mechanisms. This study aims to unravel the life cycle and driving forces of land subsidence in the Suzhou–Wuxi–Changzhou region. [ Methods ] To achieve this, a multifaceted approach was employed, including long-term and large-scale monitoring of three-dimensional seepage, stress, and strain, complemented by physical experimental models and numerical simulations. An analysis was conducted to synthesize the macro-evolutionary patterns and causal mechanisms of land subsidence and the formation of ground fissures. [ Results and Conclusion ] The findings indicate that land subsidence in the Suzhou–Wuxi–Changzhou region exhibits distinct characteristics that evolve through five discernible stages: initiation, rapid development, deceleration, stagnation, and rebound. The development of land subsidence is intricately connected to groundwater extraction, with stratum deformation arising predominantly from the compaction and dewatering of aquifers and aquitards due to pumping. During the subsidence phase, primary aquifer sand and contiguous aquitards are identified as the primary contributors to subsidence. By dissecting the causal mechanisms of land subsidence and ground fissures, this study delineates the spatiotemporal evolution of the structural compression and rebound of strata under varying conditions of deep groundwater exploitation, restriction, and prohibition, along with their respective contributions to subsidence. Ground fissures, which act as a secondary geological hazard at certain stages of subsidence, exhibit a spatial distribution and occurrence time that are closely related to groundwater levels, land subsidence, bedrock undulations, and soil-layer structural disparities. The life cycle of ground fissures can be encapsulated by the mechanical processes of compression, tension, shearing, and rebound, which highlights the triggers and critical thresholds for fissure formation due to differential subsidence. An integrated “sky–air–ground” monitoring system that can perform full-section fiber-optic monitoring in geological boreholes and amalgamates diverse technical methods is established to obtain scientific and granular data support for land-subsidence control and prevention. Furthermore, an innovative finite-element coupling interface element method customized for regional and site-specific scales is developed. This method successfully simulates the mechanical mechanisms of stratum deformation as well as the genesis and propagation of ground fissures under complex three-dimensional geological conditions, thus facilitating the precise identification and management of subsidence- and fissure-prone areas. [ Significance ] This study highlights the government’s land-subsidence control measures at various stages, which are characterized by technological innovations such as groundwater extraction restrictions and bans, thus setting a precedent for land-subsidence management and groundwater-resource stewardship in other provinces and cities across China.
By product rare earth elements deposits in China and their resource potential
, Available online  , doi: 10.12090/j.issn.1006-6616.2024081
Abstract (32) PDF (3861KB)(7)
Abstract:
China is the biggest REE (rare earth elements) producer and host the most of the REE resource. Various types of REE deposits have been reported in China with the most important alkaline -carbonatite realted REE deposits and ion adsorption REE deposits together with sand deposits and REE as by-product in other type of deposits. The most of light rare earth elements resource comes from the carbonatite related deposits, while the heavy rare earth elements mainly come from ion adsorption type REE deposits. Other rare earth deposit types also include REE placer and byproduct REE deposits. At present, the development of rare earth resources in China is mainly for the carbonatite-alkaline rock type light REE deposits and the ion adsorption type heavy REE deposits. The REE in placer deposits of as by product in other deposits have not been effectively utilized. Based on the previous research, the types and resource potential of the byproduct REE in other deposits are summarized. The results show that the deposits with rare earth by product in China include mainly marine sedimentary phosphate deposits, coal, bauxite, magmatic P and Fe-P deposits. The most important and which with huge potential rare earth resources are the marine sedimentary phosphate deposits and bauxite deposits. The associated rare earth in bauxite is mainly light rare earth, and Sc. The heavy REE (including Y) in the sedimentary phosphate deposits, especially the REE in S-P-Al-Sr rich ores from upper layer of phosphorite in Sichuan Deyang area Shifang-style phosphous deposits which contain much higher REE (more than 1% REO) than phosphorite. The heavy REE accounted for about 50% of the total REE in S-P-Al-Sr rich ores together with a variety of other crytical metals. In addition, the REE associated with magmatic (iron) phosphate deposits, coal and gold deposits are also worth paying attention to. Due to the lack of detailed exploration data, the resource of the byproduct in varied deposits in China is unclear, and the comprehensive utilization and the technology of REE recovery and extraction need to be improved. Enhancing the REE resource evaluation and comprehensive utilization technologes for the deposits with REE byproducts and making full use of the associated rare earth resources in the working mines can effectively relieve the supply pressure of heavy rare earth resources in China, which is the future development direction.
Arcuate structural belt with tectonic characteristics and numerical simulation analysis – A case study of the middle and southern segments of the Red River fault
, Available online  , doi: 10.12090/j.issn.1006-6616.2024042
Abstract (45) PDF (6530KB)(24)
Abstract:
 [Objective] The Southeast Yunnan Arcuate Structural Belt, with the middle and southern segments of the Red River fault as its main body, serves as the southwestern boundary of the Sichuan-Yunnan block and the forefront of its south-southeastward movement. However, there remains controversy regarding whether its current motion is primarily characterized by thrust-strike-slip due to compression or normal-strike-slip due to tension. This debate is strongly correlated with the complex stress-strain patterns surrounding the southeastern margin of the Tibetan Plateau. Clarification of the kinematic characteristics and genesis of the Southeast Yunnan Arcuate Structural Belt will help to understand the regional tectonic evolution. [Methods] This study utilized the remote sensing image interpretation and field geological surveys to identify late Quaternary tectonic activity evidence in the middle and southern segments of the Red River fault. A three-dimensional geological model tailored to the actual characteristics of the region was established, considering the influence of lower crustal flow, and finite-difference numerical simulations were conducted with different velocity boundary conditions set at 26.5°N. [Results] The study reveals: 1) Numerous geomorphic features and fault profiles in the middle and southern segments of the Red River fault indicate that most of the faults along the line are predominantly high-angle, with a northwest orientation and complex fault rock development. The presence of structural wedges and infilling of overlying materials has been observed in multiple typical outcrops. Additionally, there are significant undulations in the lower part of the overlying strata on both sides of the fault; 2) The numerical simulation results show that the influence of the far-field stress on both sides of 26.5°N on the horizontal and vertical deformation of the southeastern margin of the Tibetan Plateau is quite different, and the deformation is further expanded by the presence of lower crustal flow; 3) Results of numerical simulations of velocity fields, maximum shear strain rates, and maximum principal stresses demonstrate differences in surface movement trajectories, velocity distribution, stress conditions, and deformation accumulation among different models in the arcuate structural belt area, with the presence of lower crustal flow promoting deformation accumulation and making the magnitude of the velocity field closer to that of the current GPS horizontal velocity field. [Conclusion] 1) The numerous geological profiles along the middle and southern segments of the Red River fault reveal a predominantly normal-strike-slip movement, indicating that the region is currently dominated by the effects of transtension; 2) Current tectonic deformation and landscape evolution in the southeastern margin of the Tibetan Plateau are mainly controlled by two different force sources: one is the southeastward movement of materials, and the other is the arc-parallel extension and slab rollback occurring beneath the Sunda-Java subduction zone. The presence of lower crustal flow influencing the scale of tectonic deformation in this region. In the Southeast Yunnan Arcuate Structural Belt, arc-parallel extension and slab retreat play a more significant controlling role; 3) The initial curved shape of the Southeast Yunnan Arcuate Structural Belt is mainly attributed to the influence of material migration towards the southeast and the Xiaojiang sinistral strike-slip fault, resulting in continuous deformation under the constraints of pre-existing structural fabrics and the controls of arc-parallel extension and slab retreat. [Significance] The research results contribute to understanding the current activity and causes of the Southeast Yunnan Arcuate Structural Belt, and provide a quantitative analysis reference and theoretical basis for the study of tectonic evolution in the southeastern margin of the Tibetan Plateau.
Electrical characteristics and mineral search prediction of Baishawo rare metal deposit in northeast Hunan Province
, Available online  , doi: 10.12090/j.issn.1006-6616.2024060
Abstract (49) PDF (2071KB)(10)
Abstract:
Granite pegmatitic rare metal deposit is one of the most important rare metal deposit types, and it is also an important carrier of rare metal minerals. Baishawo pegmatitic deposit has been newly discovered in the east of Lianyunshan Mountain. The preliminary assessment of Baishawo mining area has great potential of rare metal resources. However, the scientific basic research on this mining area is insufficient, the mineral exploitation degree is very low, and the research degree around deep hidden granite pegmatitic vein is not high. Controlled source audio magnetotellurian method is used to detect the deep hidden rock (ore) body in the study area. Three parallel survey lines are arranged in the southeast direction of Baishawo rock mass. The conjugate gradient method is used to conduct two-dimensional inversion of the measured data. Combined with the information of drill holes and the information of elemental anomalies, the inversion results were analyzed to identify the distribution and burial depth of the concealed pegmatite veins, define the potential concealed veins in the study area, and study the geophysical characteristics of pegmatite vein mineralization, which provided the basis for the formation mechanism of fracture zone-constrained pegmatite veins.The research results provide a scientific basis for the follow-up exploration of Baishawoo mining area, and provide reliable geo
Remobilization and transferring of rare earth elements in the formation of regolith-hosted REE deposits
, Available online  , doi: 10.12090/j.issn.1006-6616.2024070
Abstract (71) PDF (2940KB)(8)
Abstract:
[Objective] Rare earth elements (REE) are indispensable for high-tech industries such as clean technologies, national defense and military industry, rendering them strategically critical minerals. In China, regolith-hosted REE deposits constitute one of the most important REE resources, supplying over 90% of the global heavy rare earth elements (HREE). Understanding the formation of such REE deposits can provide theoretical basis for the search and better utilization of these REE resources. [Methods] This paper summarizes the latest research results in recent years from the two key processes of remobilization and transferring of REE, and puts forward prospects for future research, so as to deepen the knowledge and understanding of the formation of regolith-hosted REE deposits. [Results] These deposits are primarily developed in weathering crusts of REE-rich granitic rocks, with REE distribution patterns in these crusts largely reflecting those of the underlying bedrock. The development of granitoid weathering crusts is mainly induced by chemical and biological weathering. Clay minerals and Fe-Mn (hydr)oxides, resulting from the weathering of major rock-forming minerals such as feldspar, mica, and amphibole, serve as the primary hosts for REE ions in weathered crusts. These REE ions originate from the weathering and decomposition of REE-bearing accessory minerals in bedrock, which exhibit varying degrees of susceptibility to weathering. Furthermore, metabolites such as organic acids produced by microbes can benefit the breakdown of refractory minerals like monazite and xenotime, facilitating the remobilization of REE. At the same time, microbial action can lead to significant fractionation of REE, and Gram-positive bacteria are significantly more selective to HREE than light REE (LREE). During weathering and leaching processes, REE primarily form REE-complexes within weathering crusts and then transferring by meteoric or ground water. This process is primarily controlled by factors like pH, the formation of secondary minerals, and the weathering environment. Notably, in addition to inorganic ligands such as F- and (CO3)2-, organic matter can also directly interact with REE, acting as organic ligands that aid in REE transferring. [Conclusion] Consequently, the remobilization and transferring mechanism of REE in regolith-hosted REE deposits is predominantly controlled by both chemical and biological weathering processes, which result from the interactions of inorganic and organic agents. Nonetheless, the quantitative impact of these processes on the formation of such deposits remains to be further evaluated.
Exploration prospects of the whole oil and gas system in the Permian hydrocarbon depression in the Eastern Junggar Basin
, Available online  , doi: 10.12090/j.issn.1006-6616.2024029
Abstract (77) PDF (2996KB)(8)
Abstract:
Abstract: [Objective] Multiple types of oil reservoirs, including conventional oil, tight oil, and shale oil, have been discovered in the Jimusaer Depression from the slope area to the depression area, demonstrating the characteristics of conventional unconventional ordered coexistence and complete oil and gas system accumulation. [Methods] In order to explore the rules of oil and gas accumulation in other hydrocarbon rich depressions in the Eastern Junggar, through the study of source rocks, sedimentary reservoirs, and reservoir formation, [Results] it is believed that: high-quality saline lacustrine facies source rocks are developed in the Middle Permian of the Eastern Junggar. The source rocks in the Jinan, Jimusaer, and Shishugou depressions are of large scale and best quality, and have reached the stage of mature evolution; The inherited ancient uplifts around the Permian hydrocarbon rich depression provide long-term material sources, with the development of fan deltas, braided river deltas, and saline lake sediments, forming sand conglomerates, cloudy sandstones, cloudy mudstones, etc. in an orderly manner, with the characteristics of grain sequence reservoir formation; From the edge of the basin to the depression area, conventional oil and gas reservoirs, tight oil and gas, and shale oil and gas accumulations are developed, with a complete type of reservoir formation and a complete oil and gas system development pattern. [Conclusions] The depressions in the Eastern Junggar Basin show whole oil and gas system pattern. [Significance] Under the guidance of the entire oil and gas system reservoir formation model, the southern slope of the Shishugou sag and the Lucaogou Formation of the Jinan sag are selected as important exploration zones for future exploration in the Eastern Junggar.
Petrogenesis of the Late Indosinian adakitic granites in East Kunlun and their constraints on the collision process
, Available online  , doi: 10.12090/j.issn.1006-6616.2024030
Abstract (104) PDF (4316KB)(33)
Abstract:
The collision process of East Kunlun orogenic belt is still a subject of debate. The discovery of Triassic adakitic granites in the Xiaonanchuan area of East Kunlun provides an opportunity to address this issue. The Moshigou and Bentoushan granitic intrusions are exposed in the Xiaonanchuan area. These granites primarily consist of quartz, plagioclase, potassium feldspar, and biotite. They formed during 209-208 Ma and 201-200 Ma, respectively. They have high SiO2 and Al2O3 and are rich in sodium. They also have high Sr content (398×10-6~613×10-6) and Sr/Y ratios (50~97) and are depleted in heavy rare earth elements without Eu anomalies, exhibiting typical geochemical charaterisitics of adakitic rocks. The Moshigou granite have negative whole-rock εNd(t) (-3.60~-3.34) and variable zircon εHf(t) (-1.3~+5.9), indicating their derivation from the partial melting of the thickened lower crust. The Bentoushan granite have negative whole-rock εNd(t) (-1.65~-1.55) and positive zircon εHf(t) (+3.4~+7.3), suggesting their origin from meta-basic rocks-dominated thickened lower crust with an eclogite residue. Comprehensive analysis shows that the initial collision of East Kunlun orogenic belt occurred during early Late Triassic. Subsequently, slab break-off occurred, leading to decompressional melting of the mantle and inducing partial melting of crust and formation of adakitic granites. This geological event also triggered the formation of skarn Fe deposits, polymetallic ores, and gold deposits. After late Late Triassic, the East Kunlun orogen transitioned into post-collision stage characterized by lithospheric extension and mantle upwelling, giving rise to mantle-derived magmatic rocks, A-type granites, and adakitic granites. Ultimately, the orogenesis of East Kunlun concluded after 198 Ma.
Geochemical characteristics of apatite in metabasic rocks under different metamorphic conditions: a case study from the Paleoproterozoic Trans-North China Orogen
, Available online  , doi: 10.12090/j.issn.1006-6616.2024046
Abstract (85) PDF (2311KB)(19)
Abstract:
[Objective] Apatite is a common accessory mineral, widely distributed in various types of rocks. Its U-Pb age, trace element (especially REE, Th, U, and Sr) and Sr-Nd isotopic composition can provide important isotopic geochemical information on chronology and magmatism. However, the study of its geochemical behavior at different metamorphic levels during orogenesis remains unclear. As a typical continent-to-continent collisional orogenic belt in the Paleoproterozoic, the Trans-North China Orogen (TNCO) has recorded an integrated metamorphic sequence ranging from greenschist, amphibolite to granulite facies, so it is an ideal area to study the geochemical properties of apatite during the various grades of metamorphism involving the orogenic process. [Methods] In this study, we systematically collected metabasic samples that experienced different metamorphic grades, including greenschist, amphibolite and mafic granulite in the Wutai-Hengshan area of the TNCO. We carried out detailed petrographic observations and conducted geochemical analysis on those apatite grains from metabasic rocks with different metamorphic grades. [Results] Our results show that the apatite grains from the greenschist samples contain both types of magmatic and metamorphic origin. The apatite grains from amphibolite samples are mainly metamorphic origin. By contrast, those grains from the granulite samples are intimately related to the crustal anatexis, exhibiting geochemical characteristics of magmatic origin apatite. [Conclusion] This study shows that the trace element variation of apatite can clearly reflect the influence of metamorphic grades, crustal anatexis and the coexisting rock-forming minerals with the variation of temperature and pressure conditions during metamorphism. [Significance] The new results of this study provide new constraints on our understanding of the element migration and geochemical balance within the apatite during the orogeny.
Zircon U-Pb Dating of the Dizhuanggou Formation, Changjiaoba Group in the South Qinling Belt and its Tectonic Significance
, Available online  , doi: 10.12090/j.issn.1006-6616.2024027
Abstract (48) PDF (1764KB)(11)
Abstract:
Objective: The Changjiaoba Group, located in the Foping area of the South Qinling Belt, is one the few strata of the belt that remain less well-studied. The lack of accurate definition of composition and formation age has restricted the research on the South Qinling Belt of its tectonic affinity and evolution in-depth. Method: This paper investigates the petrological and zircon U-Pb chronology of metamorphic sedimentary rocks from the Dizhuanggou Formation in the Changjiaoba Group. Results: The results show that the dominant peak detrital zircon ages of the two samples taken are approximately 810-835 Ma, with the youngest age range of approximately 600-700 Ma, indicating that the maximum depositional age is Neoproterozoic. This age spectrum differs significantly from that of the most exposed Devonian Heilongtan Formation of the Changjiaoba Group, but highly similar to that of another sample from the Foping Group, which has a minimum age peak of 718 Ma and a major peak of 810 Ma. In addition, metamorphic zircons from the Dizhuanggou Formation and the Foping Group yield ages of 207 Ma and 193 Ma, respectively. Conclusion: The distinct depositional ages in Changjiaoba Group show a complexity of its composition. Combined with the petrological and field geological features, it is believed that the Dizhuanggou Formation together with some Neoproterozoic strata of the Foping Group, formed the transitional basement of the western South Qinling Belt, which is comparable to the transitional basement of the Wudang and Yaolinghe groups east of the Ningshan Fault in the South Qinling Belt. Significance: The identification of Neoproterozoic materials in the Changjiaoba Group provides a new basis for the division of metamorphic units in the Foping area, sorting out three units with different degrees of layering and metamorphism, which in turn facilitates the understanding of the Mesozoic orogenic process in the South Qinling Belt.
Formation and evolution of the Yuncheng Salt Lake and source of the saline ions
, Available online  , doi: 10.12090/j.issn.1006-6616.2024003
Abstract (349) PDF (4974KB)(17)
Abstract:
The Yuncheng Salt Lake, nestled in the Fen-Wei graben system's heart, stands as not only China's but also the world's earliest known salt lake. Despite its historic significance, fundamental geological background of the lake remains underexplored, with a lack of consensus among researchers. This study delves into three pivotal aspects: the process of geomorphic change in Cenozoic era and the formation of Fen-Wei graben system, the Yellow River's historic course through the Sanmenxia Gorge and the resultant disappearance of the ancient Sanmen Lake, and the Fenhe River's diversion from the Yuncheng Basin and the birth of the Yuncheng Salt Lake. Our findings suggest that evolution of the lake began in the Paleogene to mid-Neogene period, influenced by the coastal Pacific domain and the Tibetan Plateau. Around 700, 000 years ago, a significant geological shift occurred: the Yellow River breached the Sanmenxia Gorge, flowing eastward to the sea. This event marked the end of the ancient Sanmen Lake and the formation of Yuncheng Salt Lake. Approximately 70, 000 years ago, during the middle Late Pleistocene, the Fenhe River rerouted, leaving the Yuncheng Basin. This change transformed the lake from an open to a closed system, solidifying its current form. The ongoing tectonic activity along the northern fringes of the Zhongtiao Mountains further sculpted the landscape, creating sedimentary depressions that amassed saline minerals, eventually giving rise to a natural salt lake through prolonged cycles of precipitation and evaporation. Salt of the lake primarily originates from deep subterranean salt formations. The primary fault controlling the lake acts as the main conduit for these salts, while the marine high magnesium dolomite from the Longjiayuan Formation in the northern edge of Zhongtiao Mountain supplies magnesium ions. These research will offer a crucial geological foundation for the ecological preservation and sustainable development of Yuncheng.
, Available online  , doi: 10.12090/j.issn.1006-6616.2023196
Abstract (154) PDF (1395KB)(9)
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Rock core disking is one of the typical phenomena in high in-situ stress environment. The geometric characteristics and section shape of rock discing are related to the state of in-situ stress, and the site where this phenomenon occurs may not be suitable for in-situ stress measurement. Based on this phenomenon, the relationship between in-situ measurement data and in-situ stress of disked rock cores is established, and in-situ stress estimation is carried out to complement the in-situ stress measurement data. Based on the relevant hypotheses and theories at home and abroad, the physical and geometric characteristics of the disked rock cores are measured, and the stress state of the original rock is combined with the stress magnitude estimation formula based on the core discing. The in-situ stress of the 30~120m position of disked rock cores in Dandong, Liaoning Province was estimated. 73 representative disked rock cores were selected to estimate the in-situ stress magnitude of the section, and the measured data of hydraulic fracturing were supplemented. The supplemented in-situ stress data were more close to the reality. Compared with other estimation formulas based on core discing, the factors taken into account are more comprehensive, the measurement accuracy requirements are lower, and the calculation results are less biased and fluctuate. The results of calculation and comparison show that this method is suitable to be used as a supplementary source of in-situ stress data.
Analysis of soaking deformation characteristics of large-thickness discontinuous collapsible loess
, Available online  , doi: 10.12090/j.issn.1006-6616.2023174
Abstract (182) PDF (1515KB)(4)
Abstract:
[Objective] The widely distributed discontinuous loess stratum in the Guan zhong Plain area of China necessitates, due to its unique stratigraphic structure, the indoor calculated value of the self-weight wetting amount in evaluating the wetting property of the foundation has a large difference with the measured value in the field. [Methods] Therefore, taking the loess stratum on the north bank of Wei he River as the research object, indoor wetting test and on-site large-scale test pit immersion test were carried out to compare the influencing factors of the difference between on-site and indoor wetting amount. [Results] The following results were obtained from the study: (1) The ratio of self-weight wet depressions between the field test and the indoor test at the site was less than 0.1, and the reasons for this discrepancy include the discontinuity and inhomogeneity of loess layers, the sampling disturbance factor of the indoor test, and the difference in immersion conditions of the field test. (2) The layer bow effect formed by the discontinuity of loess is the main reason for the difference between the indoor test and the field test. It weakened part of the upward transmitted deformation, hindered the downward transmitted gravity stress, and caused the discontinuity of the percolation process. (3) Combining the results of the stratification calculations of the four test sites, it can be seen that most of the self-gravitational wetting in the field test occurred in the Q3 soil layer. For the Q2 loess, there is a large difference between the field measured values and the indoor test values. Therefore, the Q2 loess layer is considered to have little or no wetting. [Conclusion] The shape of the saturated zone range obtained by numerical simulation is basically consistent with the field test results, and the numerical simulation method is more advantageous when observing the experimental results. When calculating the amount of wet subsidence by self-weight, the calculation method of stratification according to the age of strata can be adopted. In Q3 stratum, the method of correction coefficient in the specification is selected, and the Q2 loess stratum is determined by on-site test pit immersion test. [Significance] The research methodology of this paper can provide theoretical guidance for future engineering construction in the Guan zhong Plain.
Research on the Spatial Structure Characteristics and Formation Mechanism of the Deda Ancient Landslide Based on Microtremor Survey Method in Sichuan Province, China
, Available online  , doi: 10.12090/j.issn.1006-6616.2023183
Abstract (230) PDF (4139KB)(13)
Abstract:
The topography and geological structure of the eastern Tibetan Plateau are extremely complex. The high development density and intricate spatial structures of large ancient landslides in alpine canyon areas, such as those in the Jinsha River Basin. The hazards resulting from the creep deformation and resurgence of these ancient landslides are particularly severe. The Deda ancient landslide, situated in Deda Township, Batang County, Sichuan Province, is a significant ancient landslide influenced by the Chalong-ranbu fault activity. The spatial structural characteristics of this ancient landslide are complex, with localized resurgence deformation observed at the landslide front. This study employs various methods, including remote sensing interpretation, on-site investigations, Microtremor Survey Method (MSM), and engineering geological drilling, to further elucidate the spatial structural characteristics of the Deda ancient landslide. The research reveals that the Deda ancient landslide can be divided into three parts in plan view: Deda I landslide (I), Deda II landslide (II), and the rear wall of the Deda ancient landslide (Ⅲ). Through MSM combined with drilling verification, the study proposes a scheme for classifying the shear wave velocities of shallow and deep sliding zones, with a relative error in sliding zone depth identification generally ranging from 2.6% to 4.8%. The research uncovers that Deda I landslide features two sliding zones, with a burial depth of 18.7-20.1 m for the shallow sliding zone (S1) and 36.2-49.9 m for the deep sliding zone (S2). And the volume of Deda I landslide is approximately 8.7-12.0×106 m3. Deda II landslide has one sliding zone, with a burial depth ranging from 25.2 to 38.6 m and a landslide volume of approximately 6.3-9.6×106 m3. A comprehensive analysis suggests that the formation of the Deda ancient landslide is the result of various factors, including fault structures, rainfall infiltration, and river erosion. The complex landslide structure and its genesis are identified as the primary controlling factors for the landslide being in a state of creep deformation. The research methods and insights presented in this study can serve as a reference for the spatial identification and risk prevention of large ancient landslides in the eastern Tibetan Plateau.

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