地质力学学报

The marine environment and organic matter enrichment model of the intracontinental Upper Yangtze Craton during the Middle Triassic

TANG Song, WANG Xianfeng, CHEN Anqing, ZHOU Linlang, QI Yan, PENG Qiu, QIAN Yangjiaojiao, YUE Dali

Objective The exploration of marlstone reservoirs represents a current frontier for expanding oil and gas resources. The recent discovery of unconventional marine oil and gas in the Lei 3-2 sub-member of the Middle Triassic Leikoupo Formation in Well CT-1 reveals a new prospective area. However, the organic matter enrichment mechanisms and exploration potential of this sub-salt lagoon marlstone remain unclear, hindering further exploration. Methods This study, focusing on Well CT-1 in the central Sichuan Basin, investigates the organic matter enrichment mechanism through rock mineralogy and paleo-oceanographic geochemical proxies. This study also characterizes the reservoir properties and distribution via reservoir characterization and sedimentary facies analysis to evaluate its potential. Results The marlstone was deposited in an anoxic, deep-water lagoon of a carbonate platform with high paleo-productivity. The enrichment of organic matter, with an average total organic carbon (TOC) content of 1.16% (reaching up to 1.78%), was co-controlled by these reducing conditions and high productivity. Analyses (CT and SEM) of the high-quality "sweet spot" intervals show that the storage space is predominantly composed of nano- to micro-scale pores and microfractures, with porosity exceeding 3%. The reservoir developed in a deep-water, marlstone- and gypsum-rich lagoon within an epicontinental sea carbonate platform. Conclusion The widespread distribution of deep-water lagoons during the deposition of the Lei 3-2 sub-member is associated with a maximum flooding event. Concurrently, the prevailing monsoon climate significantly enhanced weathering and nutrient input, while the overlying regressive evaporites provided a seal for long-term and efficient organic matter preservation. [Significance] Comprehensive analysis suggests that the extensively distributed, organic-rich deep-water lagoon marlstone formed during this transgression in the intracontinental sag of the Upper Yangtze Craton is not only a viable unconventional exploration target but also likely acts as a hydrocarbon source for conventional reservoirs within the Leikoupo Formation.

Mechanisms of stress evolution and infill-well fracture disturbance in shale gas reservoirs with natural weak planes

RUAN Qi, ZHANG Liehui, ZHAO Yulong, ZHANG Deliang, ZHENG Shizhuo

Objective Mid-to-deep shale gas reservoirs exhibit a composite fracture–matrix structure, in which internal weak planes play an essential role in stress evolution and fracture propagation. Few studies have treated natural fractures as both hydraulic and mechanical weak planes simultaneously, nor has there been systematic and quantitative analysis of the impact of these fractures on four-dimensional stress evolution and fracture propagation in infill-wells during production. Methods To address these knowledge gaps, this study conducts laboratory tests to obtain the normal stiffness and hydraulic properties of weak planes, and develops a four-dimensional stress evolution model for mid-to-deep shale gas reservoirs that captures the coupled hydraulic–mechanical weakening behavior of natural fractures. The model is then used to analyze how weak planes perturb the in-situ stress field and the morphology of hydraulic fractures in infill-wells at different stages of production. Results Low-stiffness weak planes are prone to deformation, with reduced internal stress and stress concentration at fracture tips. Moreover, the disturbance of the maximum horizontal principal stress increases progressively with the growing angle between the weak plane and the principal stress direction, while the minimum horizontal principal stress exhibits a non-monotonic response: first decreasing, then increasing. During production, the deviation of stress orientation is more pronounced when mechanical weak planes are considered. Correspondingly, infill well fractures extend farther along the original maximum horizontal stress direction when not in contact with fracture zones, while the lateral expansion is enhanced and the propagation along the original maximum horizontal stress is shortened. These differences remain relatively unchanged over time, reflecting the fact that weak planes primarily influence stress disturbance in the early stages, becoming stable later on. Conclusions This study reveals how weak planes disturb the four-dimensional stress evolution. It provides theoretical guidance and practical reference for stress management and fracture optimization in hydraulic fracturing and infill development of mid-to-deep shale gas reservoirs.

Impact of middle to late Triassic climate change on organic matter enrichment in hydrocarbon source rocks of the Chang 7 Member, Yanchang Formation, southeastern Ordos Basin

LU Man, DUAN Guoqiang, ZHANG Tongxi, HUANG Tianhua, WANG Zhaoyang, LI Dewei

Objective The middle to late Triassic was a period of critical climatic transition in Earth's history. Multiple global humid climate events during this time profoundly impacted both marine and terrestrial depositional environments, facilitating the development of marine and continental source rocks. Methods This study focuses on the hydrocarbon source rocks of the seventh member of the Yanchang Formation (Chang 7 Member) in the southeastern Ordos Basin. Based on integrated elemental geochemical and molecular organic geochemical analyses, this study explores the relationship between middle to late Triassic humid climatic events and organic matter enrichment in lacustrine settings. Results The lower to middle interval of Submember 3 of Chang 7 Member (695–660 m in depth) is characterized by high total organic carbon content and good hydrocarbon generation potential. Chemical weathering indices indicate that this interval was deposited underwarmer and more humid climatic conditions, while the overlying upper portion of Submember 3 and Submembers 2 and 1 were deposited under cooler and drier conditions. By combining global characteristics of middle to late Triassic humid events with palynostratigraphy, zircon U–Pb geochronology, and carbon isotope stratigraphy, this study links the lower to middle interval of the Submember 3 and the middle to late Triassic Ladinian–Carnian humid climate event. Conclusions The findings suggest that, under the influence of humid climate events, enhanced terrestrial nutrient influxes stimulated primary productivity in the lake. Concurrently, intensified water column stratification and bottom-water anoxia created favorable conditions for organic matter preservation, leading to the deposition of high-quality source rocks. Following the event, the climate shifted towards colder and drier conditions. This reduced terrestrial input, decreased primary lake productivity, lowered oxygen depletion in the water, and led to less favorable conditions for organic matter preservation and enrichment. [ Significance] This study not only provides new evidence for paleoclimatic and paleoenvironmental reconstruction during the middle to late Triassic but also offers an important reference for understanding organic matter enrichment mechanisms during major climatic transitions in Earth’s history.

Intelligent prediction method and application of single-well in-situ stress in shale reservoirs driven by multi-source data

SHEN Baojian, LI Dan, HE Jianhua, XU Bilan, WU Yanfeng, WANG Ruyue, JIANG Rui, LI Ruixue, HUO Zhizhou, LIU Kun

Objective Deep shale reservoirs are characterized by high temperature, high pressure, elevated in situ stress, and strong plasticity. Conventional in-situ stress testing methods and log interpretation models, often calibrated under simplified laboratory conditions, suffer from limited predictive accuracy, high operational cost, and poor generalizability—challenges that constrain their utility in guiding shale gas exploration and development. Methods Focusing on a structurally complex shale gas block in southern Sichuan as a representative case, we integrated dynamic and static multi-source data across drilling, logging, testing, and production stages. Along with experimental measurements of the physical and mechanical properties of rock under different conditions, we developed a hybrid stress prediction model by combining machine learning techniques with geomechanical principles. This multi-method, log-based intelligent prediction framework enables the generation of high-resolution in-situ stress profiles for efficient shale gas development. Results In the first member of the Longmaxi Formation (Long-1 Member), organic content, confining pressure, and lamination structures significantly influence mechanical anisotropy, particularly in Beds 1–4, which exhibit stronger anisotropy than the upper beds. Based on these findings, we developed a mechanically calibrated anisotropic stress interpretation model for deep shales. Using laboratory- and field-calibrated synthetic stress datasets, we established a standardized stress database for the southern Sichuan shale reservoir. Key sensitive logging parameters, including shear wave slowness, resistivity, acoustic logs, and Young's modulus were identified via Pearson correlation analysis. An optimized XGBoost model achieved interpretation accuracies above 90% for all three principal stress components, with an RMSE of 6.63, an MAE of 3.89, and a coefficient of determination (R²) of 0.91, indicating strong robustness and generalizability. The results revealed four distinct stress barrier layers from the Wufeng Formation to the Longmaxi Formation, and the top of Bed 1 and Bed 6 acted as dominant stress-sealing interfaces. Localized compressive stresses induced by fold-related deformation further enhanced vertical stress compartmentalization and increased the minimum horizontal principal stress, thereby exerting significant influence on hydraulic fracturing performance. Conclusions The study revealed the geological factors controlling the mechanical anisotropy of the shale in the Long-1 Member, and established an isotropic in-situ stress interpretation model suitable for deep shale reservoirs accordingly. An integrated intelligent model, L-XGBoost, was adopted to achieve a prediction accuracy exceeding 90% for three-dimensional in-situ stresses. The research also clarified the development characteristics of four sets of stress barrier layers within the Long-1 Member shale and their impact on fracturing effectiveness. Significance These insights provide a scientific basis for fine-scale stratigraphic subdivision and three-dimensional well pattern design for shale gas development in the tectonically complex southeastern Sichuan Basin.

Research progress and development trends of low-friction drilling fluid for shale gas

SUN Jinsheng, CAI Wenhui, WANG Jintang, LYU Kaihe, ZHAO Ke, ZHANG Junhao

Objective Shale gas is an important unconventional natural gas resource in China, boasting significant potential reserves. Deep shale gas reservoirs generally have specific geological characteristics, such as low porosity and permeability, strong abrasiveness, and high temperature and pressure. Technical problems often arise during drilling, such as wellbore instability, friction in the long horizontal section, and large torque. Low-friction drilling fluid technology is key to safe and efficient drilling in deep shale gas reservoirs. Methods Based on an investigation of the current state of shale gas exploration and development in the world, this paper analyzes the evaluation index of drilling fluid lubricity and its drag reduction mechanisms, including, among others, lubrication film formation, rolling friction, and wettability regulation. Results This paper systematically reviews the lubrication performance and research progress of various low-friction drilling fluid systems, such as water-based and oil-based drilling fluid systems. Conclusions It is proposed that, in the future, it will be necessary to continue to strengthen the research and development of new, high-performance drilling fluid lubricants; to promote the intelligent and green transformation of drilling fluid systems; and to facilitate the multi-objective coordination between lubrication and wellbore stability technologies to meet the challenges posed by complex formations. [Significance] This research provides strong technical support for the safe and efficient development of global shale gas, for enhancing the productivity of deep oil and gas reserves.

Cover Page

2026, 32(1).

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Contents

2026, 32(1): 1-4.

Abstract (4) HTML (3) PDF (407KB)(5)

2026, 32(1): 1-2. doi: 10.12090/jissn.1006-6616.20253201

Abstract (9) HTML (5) PDF (312KB)(6)

Research progress and development trends of low-friction drilling fluid for shale gas

SUN Jinsheng, CAI Wenhui, WANG Jintang, LYU Kaihe, ZHAO Ke, ZHANG Junhao

2026, 32(1): 3-14. doi: 10.12090/j.issn.1006-6616.2025151

Abstract (102) HTML (21) PDF (826KB)(87)

The marine environment and organic matter enrichment model of the intracontinental Upper Yangtze Craton during the Middle Triassic

TANG Song, WANG Xianfeng, CHEN Anqing, ZHOU Linlang, QI Yan, PENG Qiu, QIAN Yangjiaojiao, YUE Dali

2026, 32(1): 15-30. doi: 10.12090/j.issn.1006-6616.2025055

Abstract (88) HTML (19) PDF (6043KB)(91)

Assessment of shale gas enrichment factors and delineation of favorable exploration zones in the first submember of the first member of the Longmaxi Formation, Tiangongtang area, southwestern Sichuan

LIU Shengjun, YUE Wenhan, LIU Yongyang, NI Jia, FANG Rui, DING Jieming, XU Fei, FAN Cunhui, XIA Tong, XU Lu

2026, 32(1): 31-48. doi: 10.12090/j.issn.1006-6616.2025103

Abstract (85) HTML (22) PDF (7930KB)(87)

Geochemical characteristics and geological implications of dark shale in the second submember of the first member of the Qiongzhusi Formation, Ziyang–Weiyuan area, China

XIE Shengyang, YANG Xuefeng, LI Bo, ZHAO Shengxian, ZHANG Jian, ZHANG Chenglin, LIU Jiawei, ZHANG Deliang, HUANG Shan, CHEN Xin, LIU Yongyang, ZHU Ning, WANG Gaoxiang, YIN Meixuan

2026, 32(1): 49-66. doi: 10.12090/j.issn.1006-6616.2025125

Abstract (77) HTML (17) PDF (3013KB)(89)

Hydrocarbon generation potential of deeply buried shales within the Jurassic transitional Badaowan Formation, central Junggar Basin

ZENG Zhiping, LI Baoqing, WANG Jinduo, LIU Hui, LI Shaojie, GAN Runkun

2026, 32(1): 67-83. doi: 10.12090/j.issn.1006-6616.2025111

Abstract (83) HTML (17) PDF (2322KB)(80)

Genesis of organic-rich shales in the Fengcheng Formation, southern Mahu Sag: Evidence from organic petrology, biomarkers, and isotopes

CHEN Shanhe, QI Hongyan, WANG Wei, WANG Zhenlin, LI Yanghu, TANG Fukang, GUO Shouxin, FU Zhenghang

2026, 32(1): 84-106. doi: 10.12090/j.issn.1006-6616.2025146

Abstract (97) HTML (18) PDF (2821KB)(78)

Impact of middle to late Triassic climate change on organic matter enrichment in hydrocarbon source rocks of the Chang 7 Member, Yanchang Formation, southeastern Ordos Basin

LU Man, DUAN Guoqiang, ZHANG Tongxi, HUANG Tianhua, WANG Zhaoyang, LI Dewei

2026, 32(1): 107-123. doi: 10.12090/j.issn.1006-6616.2025139

Abstract (75) HTML (21) PDF (1927KB)(79)

Refined characteristics and evaluation of shale reservoirs in the Wulalike Formation, central-western margin of the Ordos Basin

MA Mingyang, XIE Mengyu, ZHANG Dongdong, WANG Qianping, LIU Wenhui, WANG Tong, LI Fengjiao, SUN Wenyi, GUAN Xiaohan

2026, 32(1): 124-141. doi: 10.12090/j.issn.1006-6616.2025117

Abstract (83) HTML (20) PDF (6221KB)(13)

Mechanisms of stress evolution and infill-well fracture disturbance in shale gas reservoirs with natural weak planes

RUAN Qi, ZHANG Liehui, ZHAO Yulong, ZHANG Deliang, ZHENG Shizhuo

2026, 32(1): 142-158. doi: 10.12090/j.issn.1006-6616.2025144

Abstract (84) HTML (16) PDF (3948KB)(84)

Experimental study on the elastic–plastic deformation and failure behavior of deep shale with well-developed inclined bedding

HUO Tingwang, WANG Daobing, SHENG Mao, DONG Yongcun, WANG Qiuyan, HUANG Weihan, YU Bo

2026, 32(1): 159-183. doi: 10.12090/j.issn.1006-6616.2025133

Abstract (93) HTML (15) PDF (3621KB)(98)

Refined characterization of the 3D fracture complexity index based on Well-Seismic Integration

ZHANG Jinfa, FENG Yongcun, HE Bing, MA Sijia, WEI Jingyi, DENG Jin'gen

2026, 32(1): 184-196. doi: 10.12090/j.issn.1006-6616.2025059

Abstract (63) HTML (16) PDF (9867KB)(82)

Study on the influence of in-situ stress changes on shale fracture propagation considering the effect of effective stress coefficients

ZHANG Chenxi, TANG Huiying, TANG Yuxin, CHEN Yue, DENG Wenbin

2026, 32(1): 197-212. doi: 10.12090/j.issn.1006-6616.2025145

Abstract (86) HTML (18) PDF (2631KB)(80)

Evaluation of post-fracturing production efficiency in shale oil horizontal wells based on behind-casing fiber-optic monitoring

WAN Youyu, LIN Hai, ZHOU Wei, LIU Zhen, JIANG Haoyan, XIE Guiqi, LIU Shiduo, LIU Yong, YANG Jianxuan, WU Kunyu

2026, 32(1): 213-226. doi: 10.12090/j.issn.1006-6616.2025090

Abstract (86) HTML (19) PDF (2202KB)(80)

Intelligent prediction method and application of single-well in-situ stress in shale reservoirs driven by multi-source data

SHEN Baojian, LI Dan, HE Jianhua, XU Bilan, WU Yanfeng, WANG Ruyue, JIANG Rui, LI Ruixue, HUO Zhizhou, LIU Kun

2026, 32(1): 227-244. doi: 10.12090/j.issn.1006-6616.2025126

Abstract (92) HTML (17) PDF (3480KB)(107)

An intelligent lithofacies identification method for well logging of deep carbonate rocks incorporating sequence stratigraphic prior information

ZHANG Mingdi, LI Meng, LIU Yuanyang, HUANG Yuan, CUI Shuyue

2026, 32(1): 245-257. doi: 10.12090/j.issn.1006-6616.2025108

Abstract (82) HTML (31) PDF (6100KB)(101)

Governing factors and mechanisms of CO₂ microscale sweep efficiency in shale reservoirs based on causal machine learning

JIANG Jiatong, ZHANG Yihang, SONG Zhaojie, YAN Ruisheng, ZHENG Lijun, ZHANG Kaixing, LI Peiyu, HUANG Shengjie, TANGPARITKUL Suparit

2026, 32(1): 258-271. doi: 10.12090/j.issn.1006-6616.2025116

Abstract (77) HTML (17) PDF (3811KB)(87)

J.S.Lee’s scientific thought and the pioneering of China’s offshore oil industry (1954–1971): A study based on archival research and strategic practice

ZHAO Man

2026, 32(1): 272-284. doi: 10.12090/j.issn.1006-6616.2025180

Abstract (59) HTML (15) PDF (6991KB)(95)

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A 4400-Year-Old Extreme Paleo-Storm Surge Recorded in the Dongzhai Port Chenier, Hainan Island, China

ChaoQun WANG, DongXia SUN, YaoLing ZHANG, XiaoXiao YANG, Lei ZHANG, DaoGong HU

doi: 10.12090/j.issn.1006-6616.2025073

[Abstract](0) [PDF 3542KB](0)

Abstract:
Identifying paleo-storm surge deposits and extreme storm surge events holds significant scientific and practical importance for understanding the recurrence patterns of super typhoon-induced surges and predicting future storm hazards. Current research predominantly focuses on historical and modern storm surges, with less attention given to prehistoric extreme surges. This study investigates a 3.2-m-thick chenier at Wushu Village, Dongzhai Port, Hainan Island. Analyses of sedimentary structures, shell provenance, accelerator mass spectrometry (AMS)¹⁴C dating, and estimates of overtopping deposit elevation demonstrate that this chenier records an extreme storm surge event approximately 4400 years ago. The chenier's overtopping deposits accumulated on a Late Pleistocene alluvial plain landward of the Holocene highstand paleo-shoreline. Nine AMS ¹⁴C dates on shells range from 4402 to 6647 cal yr BP, exhibiting age reversals and co-occurrence of younger and older shells. The deposit is well-sorted and displays sedimentary structures diagnostic of high-energy deposition, including hummocky cross-stratification, current cross-stratification, and erosional scours. Comparative analysis of shell assemblages and ages between the chenier and underlying paleo-lagoon deposits within Dongzhai Port indicates that the chenier shells were reworked from these older lagoon sediments. The reconstructed paleo-elevation of the overtopping deposits indicates a storm surge height of 5.5 m above modern sea level. This exceeds the 4.58 m surge documented during the 2014 Super Typhoon Rammasun along the Dongzhai coast. Considering the potential influence of astronomical tides on total water levels, we infer that the extreme storm surge height 4400 years ago was likely superimposed on a contemporaneous high astronomical tide.

Evaluation of Source Rocks and Oil Source Correlation in Chang 7-Chang 6 Member of Yanchang Formation in Jingbian Area, Ordos Basin

SiWei TANG, Hui XUE, YouJun TANG, ShuMin WANG, GuangMing HU, Geng LI, FangTingYu SHI

doi: 10.12090/j.issn.1006-6616.2025050

[Abstract](5) [PDF 2632KB](7)

Abstract:
Objective The Chang 7 and Chang 6 Members of the Yanchang Formation in the Jingbian Area of the Ordos Basin constitute significant source rock intervals. However, systematic studies on their hydrocarbon generation potential and contributions to petroleum accumulation remain limited, which constrains further exploration efforts in this region. Therefore, this study integrates geochemical analytical methods to systematically characterize the distribution and the geochemical properties of the Chang 7 and Chang 6 source rocks in the Jingbian area, as well as the geochemical signatures of the crude oils from the Yan 9 and Chang 2 reservoirs in the Jingbian Oilfield. Methods By comparing the geochemical parameters between the local Chang 6 and Chang 7 source rocks and the Zhangjiatan Shale in the center of the basin, the potential sources of the oils in the Yan 9 and Chang 2 reservoirs were identified. Results The results demonstrate that the Chang 7 source rocks are high quality, with widespread distribution and considerable thickness. They are characterized by Type I-II₂ kerogen and are in the mature stage. The biomarker characteristics indicate mixed organic matter inputs, deposited in a reducing environment with low salinity. The low Pr/Ph and high C₂₇/C₂₉ regular sterane ratios further suggest that the organic matter is predominantly derived from aquatic algae and other lower organisms, consistent with a reducing, fresh to brackish water depositional environment. In contrast, the Chang 6 source rocks are of medium to high quality, containing Type II₂-III kerogen and are generally in the low-to-mature stage. The moderate Pr/Ph and low C₂₇/C₂₉ regular sterane ratios reflect a predominance of terrigenous higher plant input, deposited under a weakly reducing environment. The oil-source correlation results reveal that the Yan 9 and Chang 2 oils are of the same origin, primarily derived from the Chang 7 source rocks, with a minor contribution from the Chang 6 Member. Conclusion (1) the Chang 7 Member is the primary, high-quality source rock in the Jingbian area, superior to the Chang 6 Member in terms of thickness, lateral distribution, organic richness, and hydrocarbon generation potential. (2) Distinct biomarker signatures differentiate the Chang 7 (aquatic/algal, reducing), Chang 6 (terrigenous, weakly reducing), and distal Zhangjiatan (highly aquatic, strongly reducing) source rocks. (3) The Yan 9 and Chang 2 crude oils share a common origin and are primarily sourced from the local Chang 7 source rocks, with a possible minor contribution from the Chang 6 Member. The oils show no direct genetic link to the Zhangjiatan Shale in the basin center, supporting a predominantly local hydrocarbon sourcing model for the Jingbian area. Significance This study provides crucial geochemical evidence for a local hydrocarbon system within the Jingbian area, resolving previous ambiguities regarding oil sources and assessing the resource potential in the Jingbian Area, Ordos Basin.

Calculation Method of Reservoir Biot Coefficient Based on Griffith Criterion and Equivalent Inclusion Theory

Hui ZHANG, PEI ChenYang, ZhiMin WANG, Lei LIU, LI Jing, YiShuai LIU, ZeKun WU

doi: 10.12090/j.issn.1006-6616.2025086

[Abstract](74) [PDF 869KB](86)

Abstract:
[Objective] The Biot coefficient is defined as the ratio of the change in pore volume to the change in total rock volume, reflecting the efficiency with which pore pressure offsets externally applied total stress under loading conditions. As a key parameter in poroelastic theory, the Biot coefficient couples pore pressure with effective stress in the reservoir and plays a critical role in geostress calculation and wellbore stability analysis. [Methods] In this study, based on the equivalent inclusion theory, parameters such as the polarization factor and fracture aspect ratio are introduced to characterize the influence of fracture geometry on reservoir mechanical properties. In conjunction with the Griffith fracture criterion, a method for determining the expected aspect ratio of fractures is developed, leading to analytical expressions for the Biot coefficient in both fractured reservoirs and dissolution cavities reservoirs. [Results] The results show that the maximum errors in the calculated maximum and minimum horizontal principal stresses using the proposed Biot coefficient method are 5.75% and 6.03%, respectively, compared with field-measured geostress data, meeting engineering accuracy requirements. [Conclusion] These findings provide a theoretical basis for accurate characterization of the geostress field and efficient exploration and development of unconventional reservoirs.

Research on mechanical parameter prediction and modeling methods based on statistical regression and prestack inversion—Taking a particular area in the Bonan Depression as an example

Bin WANG, Han XIAO, XueMin NIU, RuiXuan ZHANG, Xing GE

doi: 10.12090/j.issn.1006-6616.2025084

[Abstract](67) [PDF 1153KB](83)

Abstract:
Abstract: [Objective] In the development of unconventional oil and gas, there exist problems such as complex reservoir structure and unclear rock mechanical properties. During the design of horizontal well trajectories and fracturing schemes, it is necessary to rely on rock mechanical models for segment and cluster division and design, thereby increasing the modification volume, reducing the risk of set changes, and achieving efficient development of unconventional oil and gas. The rock mechanics model can simultaneously reflect the continuous changes of mechanical parameters in the longitudinal and transverse directions with high resolution in the target area of the horizontal well trajectory. Therefore, in response to the model requirements, this paper provides a mechanical parameter prediction and modeling method based on statistical regression and prestack inversion. [Methods] Basing on the core test data and logging data, the quantitative relationship between elastic parameters and rock mechanical parameters is established and analyzed. Then, three-dimensional prestack inversion is performed using both drilling data and seismic data to obtain precise elastic parameters, including longitudinal wave velocity, density, Poisson's ratio, and Young's modulus. [Results] The application of this method in the tight glutenite reservoirs of the Bonan Sag has yielded significant and practical results. First, a robust quantitative relationship between mechanical and elastic parameters was established. The statistical regression relationship between Young's modulus and Uniaxial Compressive Strength (UCS) demonstrated a strong correlation (e.g., R² > 0.75), validating the feasibility of predicting rock mechanical strength from elastic parameters in this glutenite formation. Statistical analysis confirmed that the mechanical parameters of these highly compacted, low-porosity glutenites are primarily controlled by lithology and gravel content, exhibiting a very weak correlation with burial depth. This justifies the use of a unified predictive model across the entire studied depth interval. Second, a high-resolution 3D mechanical parameter model was constructed. A depth-domain structural model was built using logging data and a smoothed time-depth velocity field. Following attribute extraction, a comprehensive 3D mechanical parameter model for the target block was established. This model effectively overcomes the discreteness and non-continuity inherent in core and logging data, accurately characterizing the continuous lateral and vertical variations of mechanical properties. Third, the results are directed toward engineering application. To fully leverage the high vertical and lateral resolution of the mechanical parameter volume, the calculated seismic attributes were integrated into the 3D geological model based on engineering requirements. This outcome provides an accurate model for fracturing design, enabling precise assessment of the rock mechanical distribution along horizontal well sections, rational design of stage and cluster placement, optimization of pumping parameters, and enhancement of fracture conductivity. Consequently, it significantly increases the stimulated reservoir volume, effectively boosting single-well productivity and recovery rates. [Conclusion] The study leads to the following main conclusions: The integrated methodology of pre-stack inversion and statistical regression is a viable and effective solution for predicting 3D mechanical parameters in tight glutenite reservoirs. This method builds a bridge between petrophysical and seismological parameters, effectively resolving the challenge of poorly constrained rock mechanical properties in complex unconventional reservoirs. The constructed 3D mechanical parameter model provides a more reliable geological basis for optimizing well trajectories and fracturing designs. [Significance] The primary significance of this research lies in providing a reliable and scalable method for 3D rock mechanical parameter prediction and modeling, possessing substantial theoretical innovation and practical application value. It offers a dependable data foundation and a theoretical framework for defining mechanical boundaries and optimizing fracturing designs in heterogeneous tight reservoirs. This approach holds significant potential for improving fracturing efficiency and maximizing production in challenging tight glutenite formations.

MA Zhanrong, LI ZhenHong, LIU JianPing, HU AiPing, LinLin KOU

doi: 10.12090/j.issn.1006-6616.2025031

[Abstract](48) [PDF 3282KB](90)

Abstract:
[Objective] The dolomite of Ordos basin west margin complex tectonic belt Ordovician Kelimoli Formation as a high quality reservoir for natural gas exploration, its genesis mechanism and the relationship between sedimentary environment and tectonic superimposed transformation, there are still many disputes, which restricts the guidance of oil and gas exploration.[Methods] Based on comprehensive test and analysis including thin-section identification, cathodoluminescence, carbon-oxygen isotope, X-ray diffraction order, geochemical rare earth and trace elements, and strontium isotope, combined with the regional tectonic evolution process, this study explores the genetic mechanism of dolomite.[Results] Cathodoluminescence overall exhibits a relatively weak dark brown coloration with distinct ring bands, and authigenic quartz and saddle-shaped dolomite as hydrothermal minerals are visible, characterized by features of multi-stage recrystallization and burial origin. Carbon and oxygen isotope characteristics indicate that the dolomite has a burial origin. The overall order of the dolomite shows a relatively low degree, and the higher the temperature, the lower the order, suggesting that the dolomite formed in an environment with relatively high temperature and rapid crystallization rate. The rare earth element partitioning pattern is characterized by positive Ce and positive Eu anomalies, indicating that the formation process of dolomite is the result of internal fluid adjustment and redistribution within the diagenetic system under relatively closed, high-temperature, and high-pressure conditions. The lower the Sr content and the higher the Fe and Mn element contents, overall showing the characteristics of multi-stage superimposed modification under deep burial conditions. The strontium isotope values of medium to coarse-grained dolomite are significantly close to the average value of crustal source strontium isotopes, which may have been affected by crustal source strontium carried by synchronous tectonic activities.[Conclusion] Research indicates that dolomite formation is primarily attributed to deep burial, while also undergoing superimposed tectonic fluid modification. The evolution of Ordovician Krimolli Formation dolomite is closely linked to the deep fault system. During the co-deposition period, this fault system controlled the development of high-energy terraces. In the subsequent tectonic activity phase, the deep fault system became a fluid migration channel, facilitating the superimposed modification of dolomite bodies.[Significance] Research results can provide a fundamental support for the efficient exploration of oil and gas resources.

ZHU Shu, ZHANG Quan, WANG Yanbing, LI Jin, LI Renjie, HUANG Yong, LI Benliang, LIU Fucai, YAN Yuping

doi: 10.12090/j.issn.1006-6616.2025170

[Abstract](103) [PDF 2408KB](111)

Abstract:
The Jiali Fault on the southeastern margin of the Tibetan Plateau is a key boundary structure for the southeastward extrusion of plateau material. Its geometric distribution and activity are crucial for understanding the tectonic evolution of the plateau and assessing regional engineering risks. However, the precise spatial location and Holocene activity of its southeastern segment (Guxiang to Gongrigabu section) have long been controversial due to rugged terrain and thick vegetation cover. Targeting this key contentious segment, this study integrated multiple methods, including high-resolution remote sensing interpretation, field geological and geomorphological surveys, drilling and trenching exposure, and magnetotelluric sounding, to systematically investigate the fault's spatial distribution, structural characteristics, and activity. The results indicate that the southern branch of the Jiali Fault Zone continuously extends along a line from south of Guxiang, through Gionala, Jinzhunongba, to Langqiunongba. Tectonic geomorphic evidence such as fault troughs, sag ponds, pressure ridges, bedrock fault mirrors, and horizontal slickensides were identified via remote sensing and field investigations. Magnetotelluric data revealed clear low-resistivity fracture zones, and drilling core samples exposed significant fault-related rocks. This evidence collectively confirms the existence and distribution of the fault within this segment. Combined with regional paleoseismic studies, it is concluded that this segment has the potential for Holocene activity. The research further systematically analyzed the deep engineering effects potentially triggered by fault activity, including surrounding rock deterioration, cosismic offset, high in-situ stress, seismic motion amplification, water inrush and mud gushing, geothermal anomalies, and secondary disasters at tunnel portals. The research results not only provide key geological constraints for improving the tectonic model of the southeastern Tibetan Plateau but also offer indispensable scientific basis for the planning, seismic design, and risk prevention and control of major projects (such as the Sichuan-Tibet Railway) traversing the fault zone.

The Stress Effect of the 2025 Dingri M6.8 Earthquake on the Surrounding Area

chenchen zhang, YongGe WAN, ZhaoXuan GUAN, jiebin zhao, RunYan WANG, MingYue ZHOU

doi: 10.12090/j.issn.1006-6616.2025072

[Abstract](114) [PDF 5156KB](96)

Abstract:
In order to study the stress effect of the 2025 Dingri, Tibet M6.8 earthquake on the surrounding area, the multi-source focal mechanism solution data were collected in this study, and the central focal mechanism solution parameters were determined as follows: nodal plane I strike 184.37°, dip 47.67°, slip -78.10°; nodal plane II strikes 346.99°, dip 43.66°, slip -102.76°, which is diagnosed as a normal fault earthquake. By analyzing the relative shear stress and normal stress on the fault plane projected by the regional tectonic stress field, it is confirmed that the earthquake is the energy release under the action of regional tectonic stress, and it is preliminarily inferred that the node plane I is the seismic fault plane, and the Dengmecuo fault may be a seismogenic fault. Based on the elastic half-space model and the seismic rupture model, the characteristics of the displacement field and strain field induced by the earthquake are obtained: the horizontal displacement field presents the phenomenon of material gushing out from the east and west sides of the epicenter and a small amount of inflow from the north side. The vertical displacement field is characterized by subsidence in the north of the epicenter and uplift in the northeast. The distribution of volumetric strain and areal strain showed significant regularity. In addition, the estimated Coulomb failure stress increases on the southern segment of the Shenza-Dingjie Fault and the eastern segment of the Lazi-Qiongdoujiang Fault exceeds the triggering threshold of 0.01MPa, which warranting close attention to seismic activity on these faults. The Dengmecuo Fault exhibits the largest stress unloading, further validating its role as the seismogenic fault. The findings in this study provide a critical references for regional seismic hazard assessment.

Wu Chengjie^1,2，Zeng Huaien^1,2,3，Chen Jun⁴，FengYu⁵ , Li xi^2,3，WeiPengcheng^2,3,Yan Baorui^1,2

chengjie wu, HuaiEn CENG, jun chen, Yu FENG, xi li, pengcheng wei, baorui yan

doi: 10.12090/j.issn.1006-6616.2025077

[Abstract](220) [PDF 1363KB](90)

Abstract:
Accurate prediction of landslide displacement is a crucial component of landslide early warning systems. This paper proposes a landslide displacement prediction model based on Gaussian Process Regression (GPR) combined with diverse time-series feature engineering, achieving high-precision displacement prediction and uncertainty quantification. TAKING THE BAZIMEN LANDSLIDE AS AN EXAMPLE, During the feature engineering phase, displacement lag features, rolling mean of rainfall, rolling variance of reservoir water level, and displacement change rate are constructed. Additionally, temporal decomposition features including monthly and quarterly components are extracted. SUBSEQUENTLY, EMPLOY THREE-FOLD TIME SERIES CROSS-VALIDATION, ALONG WITH A GRID SEARCH SCHEME, TO OPTIMIZE HYPERPARAMETERS IN CONJUNCTION WITH THE TIME SERIES CROSS-VALIDATION STRATEGY, THEREBY MITIGATING THE RISK OF OVERFITTING IN THE SMALL-SAMPLE SCENARIO. The results demonstrate that after incorporating multi-source temporal features, the prediction coefficients of determination (R²) for monitoring points ZG110 and ZG111 at the Bazimen Landslide significantly increase to above 0.99. Metrics such as MAE, RMSE, and MAPE are substantially reduced, indicating a significant improvement in prediction accuracy. This study integrates probabilistic modeling with feature interpretability analysis. The proposed method achieves high-precision landslide displacement prediction in small-sample environments while simultaneously quantifying prediction uncertainty. It provides effective decision support for landslide risk early warning and engineering safety assessment.

Study on disaster-prone geological structure and instability mode of typical goaf landslide in Southwest mountainous area

HaoXiang ZHANG, SaiNan ZHU, LeiHua YAO, Feng GAO, LiMei ZHANG, Long YANG, WeiJia TAN, XuSheng DAI, Yu GAO

doi: 10.12090/j.issn.1006-6616.2025047

[Abstract](188) [PDF 2775KB](102)

Abstract:
Abstract: [Objective] Landslides occur frequently in the goaf areas of the mountainous regions in southwest China. The purpose of this study is to explore the commonalities and differences among such landslides, so as to formulate scientific disaster prevention and mitigation countermeasures. [Methods] This article takes the Jiguanling landslide in the limestone area, the Zhaojiagou landslide in the clastic rock area and the Shanyang landslide in the metamorphic rock area as the research objects for a comparative study. It adopts methods such as data collection and analysis, on-site investigation, multi-phase remote sensing interpretation, physical and mechanical tests of rock and soil masses and numerical simulation to analyze the similarities and differences in the disaster-prone geological structure and instability mechanism of the research objects.[Results] The research results show that when the slope has features such as steep terrain, good open-air conditions and binary structure, landslide disasters are prone to occur. The numerical simulation results indicate that under the goaf condition, the displacement of each landslide increases, the maximum shear strain increment is concentrated in the potential sliding surface and the roof area of the goaf, and the overall stability of each landslide decreases. [Conclusion] The limestone mountainous area is characterized by thick layers of hard rock interbedded with thin layers of soft rock, presenting high-intensity rock mass characteristics. The Jiguanling landslide belongs to the toppling - sliding failure mode type. The clastic rock mountainous area is affected by the interbedded structure of thin-layer fragmented soft and hard rocks, and the overall strength of the rock mass is weakened. The Zhaojiagou landslide belongs to the type of creep - tensile fracture failure mode. The metamorphic rock mountainous area presents a structure of hard rock at the top and soft rock at the bottom, with significant differences in strength. The Shanyang landslide belongs to the type of slipping-collapse failure mode. [Significance] This article provides an important scientific basis for the early identification and disaster formation pattern research of landslides in goaf areas.

Tectonic stress field characteristics in Wushi , Xinjiang and the stress impact of the Wushi M7.1 earthquake

ZeYao SONG, YongGe WAN, PeiYuan GU, MingYue ZHOU

doi: 10.12090/j.issn.1006-6616.2025085

[Abstract](247) [PDF 2767KB](113)

Abstract:
[Objective] The Wushi region in Xinjiang is located at the intersection of multiple tectonic units, making it a key area for stress concentration and release. Although previous studies have revealed some characteristics of the tectonic stress field in this region, there is still a lack of in-depth and systematic analysis regarding the potential impact of the 23 January 2024 Wushi M 7.1 earthquake on the regional stress field. Therefore, adopt more systematic focal mechanism data to conduct a detailed analysis of the regional tectonic stress field characteristics and to explore the influence of the Wushi M 7.1 earthquake on the regional stress field. The aim is to provide more comprehensive scientific references for understanding the regional seismogenic environment and predicting future seismic activity.[Methods] Using the damped stress tensor inversion method and incorporating data from multiple institutions, we analyzed the stress field in different subregions of the study area and compared the changes in the tectonic stress field before and after the earthquake.[Results] The results of the stress field inversion show that, except for the area near the Jiashi seismic group, the R value is greater than 0.5, and the azimuth of the maximum principal compressive stress in the Wushi region gradually rotates from approximately NNW in the south to near N—S in the north, the azimuth is from 168.75° to 183.45°, and plunge angle is from 6.85° to 19.58°, it is in a compressive stress state. The Jiashi seismic area cluster shows a strike-slip feature of NNE—SSW compression and NWW—SEE extension.The northern area of the Jiashi seismic shows a thrust stress state, while the southern area presents a strike-slip stress state. By comparing and analyzing the regional stress field changes before and after the Wushi earthquake, it is found that the optimal principal compressive stress direction before the earthquake was N—S direction, and deviated by 12.53° in azimuth after the earthquake, with a spatial rotation angle of 15.06°. This indicates that this earthquake had a relatively small impact on the stress field of this area, which meaning that the stress field did not undergo significant changes after the earthquake, and still remains in the compressive stress system. [Conclusion] The tectonic stress field in the Wushi region is subject to N—S compression from the collision of the Indian plate with the Eurasian plate on the western margin of the Tibetan Plateau to form a strong near-north-south horizontal compression, and the stress from the plate collision is transmitted to the northeast to the Tian Shan orogenic belt, which leads to the shortening of the crust and retrograde thrusting between the Tarim Basin and the Tian Shan. The Wushi M 7.1 earthquake had a relatively minor impact on the regional stress field. The stress system of the entire area is still controlled by deep tectonic activities. The overall stress field is consistent, but the seismic cluster in northern Jiashi is located at the junction of the northern margin of the Tarim Plate and the Tianshan Mountains, presenting a thrust stress mechanism. This area is the plate tectonic transition boundary between the Tarim Basin and the Tianshan orogenic belt.[Significance] By analyzing the characteristics of the tectonic stress field in the Wushi region of Xinjiang and the impact of the Wushi M 7.1 earthquake on the regional stress field, the characteristics of the stress field and the effect of earthquakes on the regional stress field. This contributes to a deeper understanding of the tectonic relationship between the Tianshan orogenic belt and the Tarim Basin. In addition, the northern part of the Jiashi seismic exhibits a thrust stress mechanism, which is inferred to represent a tectonic transition boundary between the Tarim Basin and the Tianshan orogenic belt. This finding holds significant implications for regional tectonic segmentation and seismic hazard assessment.

Analysis of structural surface stability in the Panlong lead-zinc mine and engineering implications

HUANG XiaoPan, WANG ChengHu, YANG ChengWei, LIU JiKun, XIAO HaiFan

doi: 10.12090/j.issn.1006-6616.2025083

[Abstract](237) [PDF 2246KB](105)

Abstract:
[Objective] The Panlong lead-zinc deposit, an important polymetallic deposit in the central Guangxi region. The increasing depth brings challenges related to high in-situ stress and structurally complex rock masses. Instabilities along structural planes have become a major geotechnical hazard. However, current understanding of the interplay between fracture geometries and stress fields remains limited. This study aims to evaluate the stability of structural surfaces at depth and their implications for safe mine development. [Methods] High-resolution data on fracture orientation and spacing were obtained through ultrasonic borehole television imaging in boreholes SK1 and SK2. Hydraulic fracturing tests were used to determine the magnitude and orientation of in-situ stresses. Stress tensor transformation and the Coulomb friction criterion were applied to estimate shear and normal stresses on structural planes and assess their slip tendency under current stress conditions. [Results] The rock mass in the Panlong mine contains steeply dipping structural planes predominantly oriented NW–NNW and NE–NEE. Cluster analysis revealed three dominant fracture sets, reflecting tectonic control from nearby faults. Furthermore, in-situ stress measurements between 500～850 m depth show S_H = 28.29～44.69 MPa, S_h = 19.46～27.09 MPa, and S_v = 14.50～22.68 MPa. The lateral stress coefficients k_H and k_h average 2.07 and 1.28, respectively, indicating a horizontal compressive regime with S_H oriented NW–NNW. Analysis of borehole breakouts and drilling-induced fractures supports the NW–NNW orientation of maximum horizontal stress. Subsequently, a total of 2,948 structural planes were analyzed. Slip tendency evaluation based on slip tendency (T_s = 0.2～0.4) shows that fractures with T_s > 0.20 are primarily distributed at depths less than 550 m. Steeper fracture planes (40°～75°) exhibit a high slip potential, indicating a higher likelihood of shear slip. NW–NNW-oriented planes exhibit both high density and high slip potential, especially when fracture aperture exceeds 10 mm. [Conclusion] It is found that the structural planes in the Panlong mine are characterized by steep dips and strong orientation clustering, primarily NW–NNW and NE–NEE, reflecting significant tectonic control. The in-situ stress regime is governed by horizontal compression, which favors the activation of reverse faults. This aligns with observed fracture development and supports the role of tectonic faults in stress field evolution. NW–NNW-oriented fractures, particularly those with low slip tendency and wide apertures, pose the highest risk for shear reactivation under current conditions and require targeted monitoring and support. Furthermore, structural planes in shallow zones (<550 m) present higher slip potential than deeper zones, emphasizing the need for depth-specific design strategies. [Significance] The findings provide a detailed understanding of structural plane behavior under deep mining conditions and provides scientific support for roadway layout optimization, support system design, and hazard mitigation.

Tectonic evolution of the Sumatran Fault: synthesis and perspective

GUO Lin, CHU Yang, LIN Wei, LEI YiYang, LIU TanJie, GUO YiLin, MENG LingTong

doi: 10.12090/j.issn.1006-6616.2025067

[Abstract](354) [PDF 3242KB](119)

Abstract:
Abstract: [Objective]Oblique convergence between the Indo-Australian Plate and the Eurasian Plate produced a ~1,900-km-long dextral strike-slip fault—the Sumatran Fault—within the overriding plate. While previous studies have extensively examined its geometry, kinematics, and seismicity, the tectonic evolution of the fault remains poorly constrained. [Methods] This study integrates multidisciplinary evidence from structural geology, geomorphology, seismicity analysis, geodesy (GPS), low-temperature thermochronology (apatite/zircon (U-Th)/He dating), and volcanic distribution mapping. We systematically synthesize data on fault segmentation, slip rates, cumulative displacement, magmatic-tectonic relationships, and regional geodynamic models to evaluate the fault’s spatiotemporal evolution. [Results] The Sumatran Fault is a highly segmented dextral strike-slip system, currently can be divided into 19 segments by geometric complexities and seismic activities. Slip rates along the fault are relatively uniform from south to north, with an average rate around ~15 mm/yr, and a total cumulative displacement estimated at approximately 20–25 km. Regionally, the distribution of active arc magmatism closely aligns with the trace of the fault, indicating a dynamic interaction between faulting and magmatism: while magma-induced crustal weakening facilitates fault development, extensional zones associated with normal faulting in turn influence the volcanic activity. Despite its tectonic significance, low-temperature thermochronological studies on the Sumatran Fault remain limited. Existing thermochronological data reveal a period of rapid uplift at ~2 Ma, likely driven by dip-slip motion along the fault. [Conclusion] A three-stage model is proposed. From an earlier period up to 2 Ma, oblique convergence accommodated primarily by the forearc faults (e.g., Mentawai Fault) and shear zones. Around 2 Ma, the Sumatran Fault initiated, coevally with the Mentawai Fault, manifesting strain localization in the overriding plate. At present, the Sumatran Fault accommodates the majority of the strain, while strike-slip motion on the Mentawai Fault has significantly diminished. The uplift phase correlates with the initial timing of the Sumatran Fault inferred from present-day slip rates and cumulative offsets, suggesting that the current throughgoing structure of the fault and the modern tectonic framework were established at the same time. [Significance] To better understand the dynamics of large strike-slip faults at obliquely convergent margins, comprehensive geochronological and structural investigations—particularly focused on fault segmentation and deformation timing—are essential. It helps to provide a paradigm for understanding strain partitioning and the genesis of trench-parallel strike-slip faults at oblique convergent margins globally, with implications for seismic hazard assessment and plate boundary reorganization.

Analysis on the three-dimensional in-situ stress state and underground cavern stability of a pumped storage hydropower project area in Xinjiang Uygur Autonomous Region

xiaofei zhang, JiMing WANG, Peng ZHANG, ZhengZheng LI, changhu li, JiangQuan OUYANG

doi: 10.12090/j.issn.1006-6616.2025076

[Abstract](259) [PDF 1517KB](109)

Abstract:
[Objective] In order to investigate the characteristics of the in-situ stress field and the stability of surrounding rock in underground caverns of a large-scale, deeply buried pumped storage power station on the southern margin of the Tianshan Orogenic Belt in Xinjiang, and to ensure the geological safety of the underground powerhouse and water diversion tunnels. [Methods] This study conducted the following work: First, two sets of three-dimensional hydraulic fracturing stress measurements were carried out in the underground powerhouse to obtain fundamental data on the in-situ stress field. Subsequently, a 3D geological model of the project area was established, and the 3D in-situ stress field was inverted using finite element numerical simulation. Finally, based on the distribution characteristics of the 3D stress field, the stability of the underground caverns was evaluated from two aspects: the rationality of the cavern axis layout and the risk of rockburst in the surrounding rock of the underground powerhouse and water diversion tunnels. [Results] The results indicate: (1)The 3D in-situ stress measurements in the underground powerhouse reveal that the maximum principal stress (σ1) ranges from 16.19 to 16.23 MPa, oriented N43.98°E–N54.44°E with a dip angle of -4.81° to 6.93°; the intermediate principal stress (σ2) ranges from 9.82 to 12.23 MPa, oriented approximately SE with a dip angle of -18.89° to -14.52°; and the minimum principal stress (σ3) ranges from 6.90 to 10.41 MPa, exhibiting a near-vertical orientation. (2)The 3D stress field inversion shows that the maximum principal stress (σ1) in the underground powerhouse ranges from 16.54 to 17.21 MPa, with an azimuth of N47.88°E–N56.32°E, while along the axis of the water diversion tunnel, σ1 ranges from 14.86 to 24.32 MPa. [Conclusion] The angles between the axes of the underground powerhouse and water diversion tunnels and the measured maximum horizontal principal stress (S_H) deviate by ≤10°from the optimal angle (62.84°) for an SHV-type stress field, which is favorable for cavern stability. Based on multiple criteria, including the rock strength-stress ratio method and Tao Zhenyu’s criterion, the surrounding rock of the underground powerhouse and water diversion tunnels is generally classified as having a slight rockburst risk. [Significance] The findings provide a scientific basis for the design and construction of the underground powerhouse and water diversion tunnels of this pumped storage power station, while also supplementing the lack of 3D in-situ stress measurement data on the southern margin of the Tianshan Orogenic Belt in Xinjiang.

NUMERICAL SIMULATION OF THE INFLUENCE OF NORMAL STRESS ON STRIKE-SLIP FAULT SUB-INSTABILITY COORDINATION

DAI ShuHong, SUN ZhaoYang

doi: 10.12090/j.issn.1006-6616.2025022

[Abstract](332) [PDF 0KB](0)

Abstract:
[Objective] In order to reveal the synergy law of strike-slip faults under different normal stresses, this study systematically investigates the instability process of strike-slip faults through numerical simulation methods. [Methods] By using the numerical simulation method, based on the FLAC3D software and the frictional-hardening and frictional-softening model, a numerical model of strip-slip fault (elastic modulus 22.3 GPa, Poisson's ratio 0.25) is established. Six normal stress schemes (0.1~3.5 MPa) are set, and the loading rate is 0.5 mm/min for all. By comparing and analyzing the spatiotemporal evolution characteristics of the shear strain field of strike-slip faults under different normal stress conditions, the influence of normal stress on the evolution of the shear strain field and fault displacement is discussed. Based on the changes of the shear strain field and fault displacement, the degree of synergy is quantitatively determined. [Results] Under the same conditions, the normal strain perpendicular to the fault direction shows a decreasing trend with the increase of time steps; while the shear strain parallel to the fault direction has similar evolution patterns at different monitoring points but with different mean values. The mean value of shear strain at monitoring point 1 is negative, that at monitoring point 11 is positive, and the mean values at monitoring points 2 to 10 tend to zero, the monitoring points refer to the locations where data changes are obtained. In the sub-unstable stage, when the fault stress accumulates to the critical point, the shear strain in the weak areas within the system increases significantly first. The range of the concentrated shear strain area gradually expands and connects, eventually forming a continuous shear strain connected area. Normal stress is positively correlated with both coseismic displacement and shear strain, and the change in shear strain energy density is also positively correlated with stress. Normal stress has an important influence on the displacement in the sub-unstable stage. With the increase of normal stress, the synergy coefficient gradually decreases and the degree of synergy increases. In the sub-unstable stage, the synergy coefficient shows a significant downward trend. [Conclusion] Normal stress significantly affects the degree of coordination in the sub-instability stage of strike-slip faults by regulating the spatial distribution and release process of shear strain energy. The increase in normal stress leads to an increase in co-seismic displacement, an accumulation and enhancement of shear strain energy, and effectively improves the degree of fault coordination. The synergy coefficient can be used as a key indicator to quantify the degree of synergy before fault instability and has application value in identifying the sub-instability state of faults. [Significance] This study clarifies the positive correlation between normal stress and the degree of coordination of strike-slip faults, providing an important scientific basis for earthquake prediction and disaster prevention and mitigation.

Geochemical characteristics of late Paleozoic-Early Mesozoic volcanic rocks in Heiyingshan, Beishan orogenic belt: indication of Paleo-Asian ocean from subduction to collision

DING YiWen, SHAO ZhaoGang, CHEN YanFei, CHEN XuanHua, LI Bing, YU Wei, XU DaXing, HAN LeLe

doi: 10.12090/j.issn.1006-6616.2025017

[Abstract](357) [PDF 3841KB](101)

Abstract:
[Objective] Regarding the tectonic evolution of the Paleo-Asian Ocean in the northern part of the Beishan orogenic belt, it is generally believed that the Carboniferous-Permian is in the stage of ocean-continent evolution. However, there is much controversy among scholars about the closure time of the Paleo-Asian Ocean. The Heiyingshan area is located in the northern margin of the Beishan orogenic belt and is a key area for studying the evolution of the Paleo-Asian Ocean in the Beishan orogenic belt. The geochemical characteristics of tuff in this area are analyzed in order to reveal its tectonic evolution background and further constrain the evolution process of the Paleo-Asian Ocean in the northern Beishan orogenic belt. [Methods] The Late Carboniferous and Late Triassic volcanic tuffs exposed in Heiyingshan area were analyzed by means of petrological and geochemical methods. Through the determination of major, trace and rare earth elements, the geochemical characteristics of the volcanic tuffs were obtained. Combined with the published regional volcanic rock age and geochemical data, the petrogenesis and tectonic setting of volcanic tuff are discussed. [Results] The results show that the Late Carboniferous volcanic tuff belongs to the peraluminous calc-alkaline series, which is enriched in large ion lithophile elements (LILE) Rb, Ba, Th and U, and depleted in high field strength elements Nb, Ta, Zr, Hf and Ti. The total rare earth element ΣREE is 74.64×10^-6~142.45×10^-6, and the light and heavy rare earth fractionation is obvious (LREE/HREE=5.14~7.49, (La/Yb)_N=4.58~6.36). The chondrite-normalized rare earth distribution pattern is right-leaning, with weak negative Eu anomaly (δEu=0.35~0.66). It shows the characteristics of I-type granite. The Late Triassic volcanic tuff belongs to the peraluminous high-K calc-alkaline series, rich in silicon and alkali, poor in aluminum and magnesium, with strong negative Eu anomaly (δEu=0.02~0.22). The chondrite-normalized rare earth distribution pattern is slightly right-leaning ‘seagull type’, enriched in large ion lithophile elements such as Rb, Th and U, depleted in incompatible elements such as Ba, Nb, Zr and Ti, depleted in high field strength elements Hf and Zr, and has the characteristics of S-type granite. The Th content of the Late Carboniferous and Late Triassic rock samples in the Heiyingshan area is 7.66~32.2μg/g, with an average of 19.24μg/g, which is much higher than the average mantle abundance and closer to the crust. The Nb/Ta values of the rock samples are 8.01~12.78, with an average value of 10.36, which is much lower than the average value of 60 in the mantle and closer to the average value of 11 in the crust. In addition, the Ba/La ratios of the Late Carboniferous volcanic rocks range from 19.19 to 24.09, with an average of 21.64, slightly higher than the continental crust average of 15.63. [Conclusion] The results show that the Late Carboniferous and Late Triassic volcanic tuffs in the Heiyingshan area were formed in the subduction and collision background of the Paleo-Asian Ocean, respectively, indicating that the tectonic environment changed from the Late Carboniferous to the Late Triassic in the Hongshishan-Heiyingshan area. The volcanic magma in this area is mainly derived from partial melting of the crust, and the Late Carboniferous volcanic rocks may be mixed with a small amount of mantle-derived materials. [Significance] The geochemical characteristics of the Late Carboniferous and Late Triassic volcanic tuffs in the Heiyingshan area provide petrological evidence for the subduction-collision process of the Paleo-Asian Ocean in the Beishan orogenic belt. The results limit the time limit of the tectonic environment transformation in the Hongshishan-Heiyingshan area in the northern Beishan, which is of great significance for understanding the final closure process of the Paleo-Asian Ocean.

Composition, tectonic framework, and evolution of the Luxi Orogenic Belt in the North China Craton

DongMing WANG, JianMin HU, YuanFang ZHAO, JiYuan YAN, WangBin GONG, ZhiGang ZHANG

doi: 10.12090/j.issn.1006-6616.2025033

[Abstract](302) [PDF 5011KB](117)

Abstract:
[Objective] The growth and evolution of the early Earth’s crust is one of the hot topics in Precambrian research. The accretion and evolution of Earth’s early crust represent one of the central scientific questions in Early Precambrian research. As one of the oldest cratons in the world, the North China Craton (NCC) has undergone a complex cratonization process accompanied by crustal growth and reformation. [Methods] Petrological, geochemical, chronological, and deformation studies are summarized to reveal the tectonic evolution of the Luxi granite-greenstone belt in the eastern NCC. [Results] There exists a series of evidence indicating late Neoarchean crustal growth, including the continental arc and arc magmatic rocks represented by the Feicheng‒Tengzhou magmatic arc and the late Neoarchean volcanic rocks, the post-collisional crustal-derived magmatism represented by the Lushan‒Yishui magmatic belt, the sedimentation of back-arc basin defined by the late Neoarchean metamorphic sedimentary rocks, and the strike-slip shear deformation caused by the oblique convergence of plates. The >2.60 Ga tonalite, trondhjemite, granodiorite (TTG suite) and supracrustal rock belt exposed in the central part of the Luxi area represents an ancient microcontinent with apparent affinity to the Jiaoliao Block. [Conclusions] Therefore, the Luxi granite-greenstone belt is an accretionary orogenic belt located on the western margin of the Jiaoliao Block, namely the Luxi Orogenic Belt. The high-angle oblique arc-continent collision and the underplating of large amounts of mantle-derived magmas represent two crustal growth modes in the horizontal and vertical directions, respectively. This orogenic belt has undergone multi-stage evolution, including formation of initial oceanic crust, subduction, and intracontinental extension from the Neoarchean to the end of the Paleoproterozoic. [Significance] In the late Neoarchean, extensive crustal growth occurred around the Jiaoliao Block in the eastern NCC, which was controlled by the early plate tectonic regime characterized by hot subduction.

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Supervisor： China Geological Survey

Sponsor： Institute of Geomechanics, Chinese Academy of Geological Sciences; Geological Society of China (GSC)

Editor-in-Chief： DENG Jun

ISSN 1006-6616

CN 11-3672/P

Post Issue Number 82-124

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