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Constraints for post-orogenic extension of the northern margin of Qaidam Basin from the Late Silurian-Late Devonian volcano-intrusive rocks
, Available online  , doi: 10.12090/j.issn.1006-6616.2023178
Abstract (6) PDF (2963KB)(1)
Abstract:
During the Early Paleozoic, the northern Qaidam Basin (NQB) tectonic belt underwent a transition from oceanic subduction to continental subduction, resulting in the formation of the renowned ultrahigh-pressure metamorphic belt along the northern margin of the Qaidam Basin. The conclusion of orogenic activities and crustal extension was marked by the deposition of molasses, as evidenced by the Maoniushan Formation. However, the commencement of crustal extension remains a topic of debate. The utilization of volcanic and intrusive rocks as probes of deep-earth rocks can offer crucial limitations for constraining crustal activities. This study presents the implementation of LA-ICP-MS zircon U-Pb geochronology and Lu-Hf isotope analyses on volcanic rocks and intrusive granites, which were initially classified as Devonian, in the Gahainanshan region located in the eastern portion of NQB. The findings indicate that the dacite of the Mauniushan Formation has a zircon U-Pb age of 423 Ma, whereas the intrusive granite has a U-Pb age of 370 Ma. This suggests that the volcanic eruption occurred during the Late Silurian period, while the intrusive granite crystallized during the Late Devonian period. The Zircon Lu-Hf isotope analysis indicates that the Late Devonian dacite has a concentrated εHf(t) range of -12 to -8 and a two-stage Hf model age between 2.15-1.93Ga, indicating its derivation from ancient crustal materials. The later intrusive granite, however, displays an εHf(t) range of 3-11 and a two-stage Hf model age between 0.8-1.1Ga, suggesting that it mainly originated from the partial melting of new crustal materials. After conducting a comprehensive analysis of regional geology and petrology, it can be inferred that the Late Silurian-Early Devonian period was marked by a significant orogeny caused by continental deep subduction, which resulted in the thickening of the NQB crust. This process, in turn, triggered the melting of the thickened Oulongbuluke crust, leading to the formation of volcano-magmatism. In the Late Devonian, the extensive extension caused by the delamination of the thickened crust led to the upwelling of the asthenosphere material, thereby resulting in the partial melting of new crustal material. Thus, it can be concluded that the formation time of the Maonisuhan Formation in the region is highly variable, and therefore cannot be used to represent the end of orogeny and lithosphere extension in a general sense. Only the late Devonian igneous rocks provide evidence that the northern margin of Qaidam underwent significant crustal extension.
Metallogenic regularity of antimony-gold deposits in Longlin-Xilin district in western Guangxi, South China
, Available online  , doi: 10.12090/j.issn.1006-6616.2023120
Abstract (9) PDF (2521KB)(5)
Abstract:
Antimony deposits are characterized by simple minerals assemblage, and often lack minerals suitable for testing and analysis. Therefore, the metallogenic ages, sources of ore-forming materials, and genesis of antimony deposits are controversial. The antimony metallogenic province in South China accounts for over 83% of China's antimony resources. The Dian-Qian-Gui antimony metallogenic belt is located in the western of the South China antimony metallogenic province. In this study, we summarized ore-bearing stratums, rock lithologies, host structures, and the relationship between gold and antimony of 86 deposits in the Longlin-Xilin antimony-gold district, the middle segment of the Dian-Qian-Gui antimony metallogenic belt. Combined with the geological investigation of typical deposits and the distribution of magmatic rocks, the relationships among antimony mineralization with clastic rocks and magmatic rocks were discussed. We concluded that: (1) nonographitic black shales and pyritiferous sandstones and siltstones are favorable  for antimony mineralization. These strata have high antimony background values, which may have provided ore-forming materials. (2) The felsick intrusions may provide heat or Sb and S for the antimony mineralization. (3) Statistical results show that independent antimony and gold deposits dominate in the Longlin-Xilin district, and few deposits are characterized by intergrowth features of antimony with gold. These indicate that antimony deposits in the study area may be the superposition of fluids from different sources, and a small number of deposits maybe resulting by the Sb-Au separation from same ore-forming fluid. In the latter case, the precipitation of stibnite consumed H2S in the ore-forming fluid, resulting in other metals that migrated in the form of complexes (such as Au and Hg) to precipitate at the same time. The competitive relationship between Sb and Au led to that the contents of Sb, Au show a negative correlation in antimony-gold deposits. (4) The district has experienced NS-striking compression in the Indosinian, followed by the NW-SE-striking compression in the middle-late Jurassic. The intersection of NWW-SEE-striking and NE-SW-striking faults is the favorable ore-bearing space. The NWW-SEE-striking faults were strike slip in response to the NW-SE-striking shortening deformation, whereas the NE-SW-striking faults exhibited transpression. As a result, the NE-SW-striking faults are not beneficial than the NWW-SEE-striking faults. Based on these studies, we proposed the ideal direction for prospecting in Longlin-Xilin district: (1) Black shale and pyritiferous siltstones of the Yujiang Formation that in the core of the Xinzhou anticline are the favorable stratums for antimony prospecting. (2) Concealed intrusion in the NWW-SEE-striking Nongsang-Shijaizhai fault (the Longlin County) and the intersection area of the NWW-SEE-striking Douhuang-Xilin fault and the NE-SW-striking fault (the Xilin County) are the favorable spaces for antimony exploration. The abovementioned discussion will enhance our understanding of the genesis and metallogenic regularity of antimony deposits and provide the directions for exploration.
The late quaternary slip rate and paleoearthquakes of the Cuopuhu section of the Litang-Yidun fault, western Sichuan
, Available online  , doi: 10.12090/j.issn.1006-6616.2023060
Abstract (17) PDF (3192KB)(3)
Abstract:
The Litang-Yidun fault is a left-hand strike-slip active fault that extends for about 130 km in the Sichuan-Yunnan rhombic block. Studying the tectonic activity history of the Litang-Yidun fault is helpful to understand the theory of material eastward escape-slip of the Qinghai-Tibet Plateau. In this paper, the Cuopuhu section of the Litang-Yidun fault is selected as the research object, and the paleo-seismic events of the Cuopuhu section are explored using methods such as field survey, trenching and 14C dating. Two exploration trenches were excavated at the foothills of Dongou mountain to identify the cutting relationship between faults, the strata, the sedimentary characteristics, the fault motion and other characteristics, combined with the 14C dating results, a total of 4 paleo-seismic events were identified. Event I occurred before BC3382±60a; Event II occurred between BC3382±60a~BC1094±51a; Event III and Event IV both occurred after AD1330±44a. According to the last glacial moraine ridge, the average slip rate of the Cuopuhu section since the Late Pleistocene is 4.15±0.5mm/a.
Quantitative evaluation of upper limit pressure and storage capacity of gas-top sandstone reservoir-type gas storage
, Available online  , doi: 10.12090/j.issn.1006-6616.2023075
Abstract (55) PDF (650KB)(7)
Abstract:
Increasing the upper operating pressure is the most direct, effective and comprehensively beneficial solution to increase the working gas volume of the reservoir. This paper quantitatively evaluates the operating cap pressure and reservoir capacity of the 1-29 reservoir in Nambourg field, Jidong, on the basis of the in situ measured minimum principal stress in the mine wells, and the results show that: based on the minimum principal stress criterion, the cap pressure corresponding to the occurrence of tensile damage in the cap layer is the lowest, i.e., based on the measured minimum principal stress, the operating cap pressure of the 1-29 reservoir in Nambourg field is determined to be 27.20 MPa. effective reservoir capacity calculation model, taking into account the water content, residual water and edge porosity of the gas layer, the wave coefficient of the oil layer, the efficiency of the gas drive fluid and the utilization rate of the oil-bearing space, etc., the upper limit pressure is raised from the original formation pressure of 22.50 MPa to 27.20 MPa, and the effective reservoir capacity of the reservoir is increased from 15.46×108 m3 to 18.14×108 m3, with an increase of the capacity of the reservoir of about 17.3%, which is expected to significantly improve the economic benefits of the gas storage reservoir, and the results of this paper have certain reference value for the quantitative evaluation of the upper pressure limit and reservoir capacity of other underground gas storage reservoirs.
Development Characteristics and Susceptibility Assessment of co-seismic geological Hazards in Jishishan Ms6.2 Earthquake, Gansu Province
, Available online  , doi: 10.12090/j.issn.1006-6616.2024009
Abstract (60) PDF (4176KB)(24)
Abstract:
On December 18, 2023, an Ms6.2 earthquake occurred in Jishishan County, Gansu Province. The co-seismic geological hazards induced by the earthquake seriously threaten the safety of personnel and property. It is very important and urgent to summarize and analyze the development law of co-seismic geological hazards and the assessment of county susceptibility in time to support post-earthquake recovery and reconstruction. Through emergency investigation and field investigation and result analysis, it is found that the overall development degree of co-seismic geological hazards in the earthquake area is not strong, and the scale is mainly small, which is 3 categories and 8 sub-categories of hidden dangers of landslides, most of which are distributed in the loess hilly area. Based on the Pearson correlation coefficient and random forest Gini coefficient analysis method, 15 influencing factors were selected, and the random forest model was used to assessment the susceptibility of co-seismic geological hazards in Jishishan County (AUC = 0.961). The results show that the area of extremely high susceptibility area accounts for about 8.67%, mainly distributed in Hulinjia Township, Xuyijia Township, Liugou Township and other townships, and the susceptibility classification structure of counties and townships is consistent with the density distribution of hidden danger points, with high accuracy. Based on this, the purpose of predicting the spatial distribution of potential geological hazards other than the hidden danger points is realized to a great extent, which can provide zoning support for the post-disaster recovery and reconstruction planning of Jishishan County.
Landslide Displacement Prediction Based On EEMD-CNN-LSTM Model
, Available online  , doi: 10.12090/j.issn.1006-6616.2023145
Abstract (101) PDF (1892KB)(13)
Abstract:
The prediction of landslide displacement is an important part of landslide monitoring. Although time series methods based on deep learning paradigms have achieved some success in predicting landslide displacement, the non-stationary, periodic, and trending characteristics of landslide displacement data make it prone to overfitting in current time series models. In this paper, we propose a landslide displacement prediction model based on the combination of Isolation Forest (IF) anomaly detection, Ensemble Empirical Mode Decomposition (EEMD), Convolutional Neural Networks(CNN), and Long Short-Term Memory (LSTM) neural network, which addresses the volatility of landslide displacement data and the characteristics of displacement composed of periodic and trending components. The Baijiabao landslide in the Three Gorges Reservoir area, which is affected by rainfall, is selected as the research object. The IF algorithm is used to detect anomalies in the original landslide displacement data. The trend and periodic components of the landslide displacement are extracted based on the EEMD method, and the overall displacement is predicted using the LSTM model. The accuracy of the prediction is evaluated using four indicators: RMSE, MAE, MAPE, and R2. The results show that the proposed EEMD-CNN-LSTM model is superior to traditional LSTM models, random forest methods and EEMD-LSTM methods under both external influences of rainfall and without rainfall, which can greatly reduce overfitting and improve the accuracy of prediction.
LATE QUATERNARY FAULT ACTIVITY AND MECHANISM OF STRONG EARTHQUAKE AROUND THE BOUNDARY ZONE OF THE ORDOS ACTIVE BLOCK, IN CENTRAL CHINA
, Available online  , doi: 10.12090/j.issn.1006-6616.2023154
Abstract (53) PDF (2659KB)(17)
Abstract:
The Ordos block with typical boundary zone activity is located in the center of the Chinese Mainland. Under the joint influence of the remote action of the Tibet Plateau at the southwest and the Pacific Plate at the east, the tectonic activity and deformation of each boundary zone of the Ordos block have obvious specificity and differences. This paper systematically summarizes research achievements on active faults and the seismogenic mechanism of strong earthquakes around the Ordos block over the past few decades. The difference of fault activity in each boundary zones have determined the differences of strong earthquake breeding tectonic environment. At the southwest of the block, the faults are mainly characterized by strike slip, reverse strike slip, and thrust due to the influence of the northward compression and expansion of the Tibet Plateau, resulting in complex structural deformation styles within the boundary zone. In the northern section of the western boundary, the latest expansion boundary of the Tibet plateau is characterized by a dextral movement along the Sanguankou- Niushoushan fault. The Yinchuan Basin in the northern section of the west boundary zone is a typical fault basin, with the basin-controlling faults exhibiting dextral strike slip characteristics, and earthquakes are mostly of a normal strike slip type. On the northern boundary, the normal fault on the north side of the Hetao Basin is its controlling structure, and historical and ancient earthquakes characterized by normal faults are mostly concentrated on boundary faults. The southern boundary is mainly the Weihe basin, which has a relatively complex structure and is composed of two sets of normal faults. Large historical earthquakes mostly occurred on the southern edge, and moderate earthquakes also occurred in the central and northern parts of the Weihe basin. The Shanxi graben system on the eastern boundary is composed of multiple rift type basins, with strong seismic activity in the south and weak activity in the north. The northern basin is influenced by the Zhang-bo tectonic belt, and the basin trend and fault movement properties have undergone significant changes, with most of them having the conditions for ~M7. Overall, it is believed that the typical characteristics of fault activity are in the boundary zones around the Ordos active block. In the future, strong earthquakes will mostly occur in seismic gaps with long periods of large earthquakes, or in the transition and intersection areas of tectonic zones. It is also important to pay attention to the possibility of M 6-7 earthquakes occurring in some newly formed faults and fault segments without rupture.
Fracture network complexity of tight sandstone and its influencing factors
, Available online  , doi: 10.12090/j.issn.1006-6616.2023128
Abstract (49) PDF (1766KB)(5)
Abstract:
The fracture network complexity analysis of tight sandstone plays an important role in hydraulic fracturing optimization, fracture network prediction and fracture modeling. Based on the experimental study on the dynamic evolution process and main controlling factors of complex fracture network in sandstone, the complexity analysis of fracture network is carried out by deeply discussing the fractal and multifractal spectrum characteristics of fracture network. The results show that the initiation and propagation of cracks run through the whole process of stress-strain, and the complexity of fracture network is mainly controlled by its own microscopic fabric characteristics, and has obvious scale and confining pressure effects. The fractal dimension of the three-dimensional fracture network and the average spectral width of the multifractal spectrum can represent the complexity and heterogeneity of the spatial distribution of the fracture network, respectively. The higher the content of quartz, feldspar and other brittle minerals in sandstone, the larger the porosity and the smaller the particle size, the more complex the spatial distribution of fracture network and the weaker the heterogeneity. Clay minerals are not conducive to the formation of complex fractures. The larger the compressive strength and elastic modulus, the more complex the spatial distribution of the fracture network and the weaker the heterogeneity.
Surface deformation and tectonic implication of the late Quaternary Bue Co strike-slip fault system, mid-western Qiangtang block
, Available online  , doi: 10.12090/j.issn.1006-6616.2023086
Abstract (414) PDF (2863KB)(24)
Abstract:
The Bangong Lake-Nujiang Suture Zone (BNSZ) serves as a significant boundary within the Tibetan Plateau, separating the Qiangtang and Lhasa terranes. Studying the late Quaternary geometric structure and deformation characteristics of (conjugate) strike-slip faults in this boundary zone is crucial for gaining a better understanding of the spatial responses and tectonic model resulting from the collision of the Indo-Eurasian plates . The Bur Co fault system, located in the western BNSZ, consists of the NE Bur Co Fault and the NW Lamu Co Fault. By employing remote sensing interpretation and conducting field geological investigations, researchers have clarified the late Quaternary structural and surface deformation characteristics of these two faults. The results demonstrate significant fault activity since the late Quaternary period, with evidence of recent large earthquakes causing surface ruptures along both faults. Consequently, it can be inferred that the recent active intensity of the NW and NE faults in the western part of the BNSZ might be similar. Furthermore, it is likely that the current deformation of the southern boundary of the Qiangtang Block is influenced by both faults, which has extended into the internal of the block. These findings provide further support for the hypothesis that the material within the Tibetan Plateau continues to expand eastward and northward due to the activity of strike-slip faults and normal faults, driven by the weaken mid-lower crustal flow.
The Early Cretaceous extensional deformation in the southeastern Beishan Range, central Asia: Insights from 2D seismic reflection profiles and apatite fission track thermochronology
, Available online  , doi: 10.12090/j.issn.1006-6616.2023151
Abstract (56) PDF (7205KB)(25)
Abstract:
To better understand the timing, processes, and dynamic mechanisms of the enigmatic late Mesozoic tectonic transition from contraction to extensional deformation in the southern Central Asian Orogenic Belt (CAOB), detailed structural analysis and apatite fission track thermochronology were conducted in the southeastern Beishan Range. Field observations show that Lower-Middle Jurassic strata have been strongly deformed by numerous thrusts and folds. 2D seismic reflection profiles reveal two NE- to NEE-striking normal faults. The Suosuojing fault is a SE-dipping low-angle listric normal fault, and the Wudaoming fault is a NW-dipping high-angle normal fault. The normal faults cut the early-formed fold and thrust system, indicative of the contraction-extension transition. The Suosuojing and Wudaoming faults border the Early Cretaceous Zongkouzi Basin to the northwest and to the southeast, respectively. The Zongkouzi Basin has a graben geometric, in which Lower Cretaceous strata display typical growth-strata relationships, suggesting that the normal faults were active during the late Early Cretaceous. Thermal history modelling results by apatite fission track data show that the Suosuojing fault footwall experienced rapid cooling during 132~110 Ma. This phase of rapid cooling was intimately related to footwall exhumation during normal slip of the Suosuojing fault. We argue that the late Mesozoic intracontinental contraction-extension transition in the southeastern Beishan Range may have occurred between ~133 Ma and ~129 Ma in the late Early Cretaceous. Collapse of thickened crust and coupled mantle upwelling triggered the Early Cretaceous extensional deformation in the southern CAOB.
LIU Xinshu1,2,WANG Wei-(RZ)1,2,BAO Hong1,2,GONG Tingnan1,2,3,ZHAN Liqing1,4,LIU Xiaochun1,2,ZHAO Yue1,2
, Available online  , doi: 10.12090/j.issn.1006-6616.2023172
Abstract (73) PDF (2567KB)(17)
Abstract:
The East Antarctic Shield records various geological processes from Archean to Phanerozoic. The Prydz Bay belt was closely related to the evolution of the Rodinia and Gondwana supercontinents, but the geological history of the region remains unclear. The mineral assemblage of the spinel-cordierite granulite from the Mirror Peninsula in the Prydz Bay belt includes spinel, cordierite, biotite, sillimanite, minor garnet, K-feldspar and ilmenite. Combined with paragenetic mineral assemblages and mineral compositions, the phase equilibrium modelling constrains peak pressure-temperature(P-T) conditions to 870~900°C, 6.3~6.9kbar, and retrograde P-T conditions to 810~820°C, 4.9~5.3kbar. Based on reintegrated spinel compositions, the formation temperature of spinel was constrained to 750~810℃, comparable with those retrograde conditions constrained using phase equilibrium modelling. Zircon grains commonly show core-mantle-rim structures in cathodoluminescence (CL) images. The core domains show a wide age range between 613±6.6Ma to 877±8.6Ma with a maximum age of 916±10.9Ma, which are younger than typical age of Greenvillian events. The bright rims of zircon grains yield a weighted mean age of 525.7±8.2Ma with a wide range of Th/U (0.06~1.23), mostly higher than 0.1. Combined with previous results, the medium- to low-pressure granulite facies metamorphism as revealed by the spinel-cordierite granulite could be interpreted to form in an orogenic process from collisional to subsequent post-collisional stage, possibly associated with the assembly of the Gondwana supercontinent.
Seismic Tectonic Environmengt and Synseismic geological Hazard Characteristics of Maerkang M6.0 Earthquake Swarm in the Western China
, Available online  , doi: 10.12090/j.issn.1006-6616.2023038
Abstract (79) PDF (4655KB)(6)
Abstract:
The tectonic background of the Markang earthquake swarms is complex, and the coseismic earthquake disasters are developed. Studying on the tectonic environment of earthquakes is the basis for analyzing and predicting earthquake risks. Studying on the distribution laws and characteristics of geological coseismic geological disasters of the earthquake swarms type is conducive to revealing the differences of geological disasters induced by different types of earthquakes, and could provide guidance for the prevention and prediction of secondary geological disasters induced by earthquake . Based on the seismic sequence data, regional tectonic environment research results, regional crustal deformation research data, and geological disaster data in the short term after the earthquake, this paper discussed the regional and deep tectonic environment of the Markang M6. 0 earthquake swarms and the main factors controlling the coseismic geological disasters. The research shows that: (1) the Markang earthquake swarm of magnitude 6.0 is a deep stick slip earthquake that occurred in the strong seismic gap on the secondary fault in the Bayan Har block with strong activity on the peripheral boundary, and multiple earthquakes with similar magnitudes may be the result of the secondary fault rupture of the Songgang fault and the successive rupture of the partition between them; (2) A total of 83 new geological hazards were induced by the earthquake, resulting in 106 more deformation at the hidden danger points of the reservoir, and many high level landslides and a series of earthquake cracked mountains. After the earthquake, the areas of the extremely high, high and medium risk geological hazards in Caodeng Township accounted for 1.62%, 4.80% and 12.37% respectively; (3) The control factors of coseismic geological disasters from primary to secondary are seismogenic fault and its linkage fault, earthquake magnitude and energy attenuation, terrain slope and height difference, rock mass structure and structural plane density. The intersection area of Songgang fault and Longriba active fault that caused the earthquake has a high risk of strong earthquakes in the future, and the risk of geological disasters around the earthquake generating fault and the fault with its linkage effect is high during earthquakes. The research results can provide reference for understanding the earthquake risk around and inside the Bayan Har block and predicting the secondary disasters in potential earthquakes.
Research on regional dynamic background and prevention of Longyun Coal Industry 10.20 rock burst accident in Shandong Province
, Available online  , doi: 10.12090/j.issn.1006-6616.2023094
Abstract (93) PDF (1446KB)(21)
Abstract:
The stability of surrounding rock of mine roadway, traffic tunnel and other underground chamber is closely related to the regional ground stress environment of rock mass. Based on the 10.20 rock burst accident in Longyun Coal Industry, through in-situ stress measurement and monitoring, we have preliminarily revealed the present earth stress environment in the shallow crust of western Shandong Province. According to the characteristics of the present ground stress field near Longyun Coal mining area, the paper discusses the dynamic background of the rock burst accident, and puts forward corresponding prevention and control suggestions from the perspective of ground stress. The results show that the principal stress is directly proportional to the depth, the maximum horizontal principal stress is 3.48~20.76MPa, and the gradient is 0.0182MPa/m as the depth increases. The minimum horizontal principal stress is 3.44~14.95MPa, and the gradient is 0.0130MPa/m as the depth increases. The maximum horizontal principal stress azimuth is N43°~89°E, and the average azimuth is N75°E. The tectonic action on the surface of the crust is mainly horizontal movement, but with the increase of depth, the tectonic action gradually changes to vertical movement. The dynamic mechanism of rock burst accident in Longyun Coal Industry is mainly due to the large buried depth in the accident area and the vertical stress environment.
Drilling revealsthe Late Quaternary activity of the Liaocheng-Lancao fault: Discussion on the seismogenicmechanism of the 1937 Heze M7.0 earthquake
, Available online  , doi: 10.12090/j.issn.1006-6616.2023088
Abstract (145) PDF (5349KB)(13)
Abstract:
The North China Plain (NCP) is one of the most populated and economically developed areas in China, and is a region with high level of seismic hazards. Study on the Quaternary activity of the faults and the seismogenic mechanism of the large earthquakes in NCP is conducive to exploring the seismogenic pattern of intraplate earthquakes and reducing the damage caused by seismic hazards.The Liaocheng-Lancao fault is an important buried deep major fault in the south-central part of the NCP. In this study, the activity of the Liaocheng-Liaocao fault is finely studied by combining shallow seismic exploration, drilling and Quaternary dating methods.The Bachengsi drilling reveals that the southern segment of the Liaocheng-Lancao fault displaces the bottom boundary of the Holocene and is an early Holocene active fault. It also reveals four paleoseismic events since the Late Pleistocene, with vertical displacement of 1.2±0.2-3.7±0.2 m for a single event. Based on the stratigraphic offsets in the boreholes, the average vertical slip rate of this fault is calculated to be about (0.1±0.05) mm/a for the early Late Pleistocene and (0.35±0.04) mm/a for the late Late Pleistocene-middle Holocene. Based on the distribution of isoseismic lines and surface ruptures of the 1937 Heze M 7.0 and M 6 earthquakes, the Xiaoliu-Xieyuanji fault and the Dongming-Chengwu fault are considered to be the seismogenic faults. The Liaocheng-Lancao fault has a good controlling and restraining effect on the accumulation of stress and the occurrence of earthquakes in the area, and is the seismic controlling fault of this earthquake.
Mesostructure and strength characteristics of granite under freeze-thaw cycles based on CT image processing
, Available online  , doi: 10.12090/j.issn.1006-6616.2022126
Abstract (77) PDF (1291KB)(7)
Abstract:
With the deepening of railway engineering in west Sichuan, a large number of tunnel rock masses in alpine region are affected by freeze-thaw effect. Freeze-thaw cycles lead to the deterioration of surrounding rock properties, which is one of the important factors to reduce rock strength. In this paper, the granite of a railway tunnel along Ganzi-Kangding is taken as the research object. The nanoVoxel-4000 series CT scanner is used to scan the rock samples with high resolution. The threshold segmentation method is used to binarize the scanned images. After stacking the images, a CT scan stereo model is constructed. The box-counting dimension of the sample image after binarization is calculated by fractal theory. Using threshold segmentation method to process the image can better extract the pore distribution characteristics in the image. Combined with the data obtained from the mechanical test, the relationship between the meso-structure evolution and strength change of rock caused by freeze-thaw was explored. The results show that under the action of 20 freeze-thaw cycles, the fractal dimension shows that the internal complexity of rock decreases slightly, but the overall integrity is still good. The internal structure of rock is dominated by unevenly distributed micropores, and the porosity increases gradually. While the complexity of rock structure does not change significantly, the long-term strength and creep characteristics of rock show a decreasing trend. This study provides a reference for the application of fractal theory in rock meso-structure evolution and the study of rock meso-structure and strength evolution.
Evaluation of stress and rock mechanics parameters in the carbonate rock based on cross-dipole acoustic logging——A case study of the Shunbei 4 zone
, Available online  , doi: 10.12090/j.issn.1006-6616.2023110
Abstract (87) PDF (1361KB)(15)
Abstract:
Rock mechanics parameters and single well in-situ stress are the basic parameters for basin tectonic stress field simulation, oil and gas field drilling and completion and reservoir fracturing stimulation design. Based on the experiment of rock mechanics and array acoustic waves, the rock mechanics parameters and in-situ stress of the carbonate reservoirs of the Lower Paleozoic Ordovician Yingshan Formation and Yijianfang Formation in the Shunbei 4 zone were analyzed. The results show that the Young's modulus of the Yijianfang Formation and the Yingshan Formation in the Shunbei 4 zone is 50-89 GPa, the compressive strength is 99-136 MPa, and the Poisson's ratio is 0.25-0.32. Combined with logging interpretation of reservoir classification, the differences in rock mechanics parameters of different reservoir types were compared and analyzed. From type I, type II, type III to non-reservoir, the Young's modulus and compressive strength of carbonate rock increased significantly, while Poisson's ratio is not much different. The maximum horizontal stress of the Yijianfang Formation and the Yingshan Formation in the Shunbei 4 zone is 200-225 MPa, and the minimum horizontal stress is 125-160 MPa; from type I, type II, type III to non-reservoir, the maximum horizontal principal stress of carbonate rocks The maximum horizontal maximum horizontal stress increases significantly, while the minimum horizontal stress has little difference. There are early cracks and caves in carbonate rocks, which significantly weaken the rock's ability to resist external forces and reduce the rock's compressive strength and Young's modulus.
Regional geological characteristics and evolution history of the Gagarin region on the far side of the moon
, Available online  , doi: 10.12090/j.issn.1006-6616.2023035
Abstract (163) PDF (3231KB)(20)
Abstract:
This paper takes the Gagarin region on the far side of the moon as the research object, interprets multi-source remote sensing data, and reveals the geological characteristics of the typical region on the far side of the moon through quantitative statistics of geological elements, distribution characteristics and genetic analysis, and then discusses the regional geological evolution history of the Gagarin region. The relationship between the geological characteristics of this area and the evolution of the moon has been preliminarily established. The results show that: (1) The longest deep fault in the whole moon developed in the region is the result of the combined action of the South Pole Aiken impact event and the lunar thermal expansion and other internal and external stresses. (2) The linear anomalies of the thickness of the lunar crust extending outward from the South Pole-Aiken Basin extend to the major basins on the frontal side of the moon, indicating that the influence range of the South Pole-Aiken basin on the far side of the moon can radiate to the frontal side of the moon at the depth of the moon. (3) The variation of the number and area of impact craters in the Gagarin region on the far side of the moon is related to the evolution of the Earth-Moon system and the Solar System. (4) According to the quantitative statistical results of the impact crater and the dating results of the basalt units, the regional geological evolution history was clarified, and the active periods of geological processes in Gagarin region are divided.