Lithosphere最新文献

{"title":"Geomechanical Simulation of 3D Directional Borehole Circumference in Deep Composite Salt Formation","authors":"Shiyuan Li, Chenglong Li, Zhaowei Chen, Wenbao Zhai, Yajun Lei, Jiawei Cao","doi":"10.2113/2024/lithosphere_2023_212","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_212","url":null,"abstract":"Composite salt formation is a high-quality caprock for oil and gas resources. The accident encountered in composite salt formation drilling is a big problem to be solved in the drilling process. According to statistics, nearly 50% of drilling accidents occur in composite salt formations. The composite salt formation is mainly composed of salt, gypsum, and interbed mud, and the lithology is complex and changeable. Therefore, it is very important to study the deformation mechanism and leading influencing factors of composite salt formation in view of the problem of frequent accidents in the drilling process. In this article, the creep parameters based on the constitutive equation of creep of salt rock are obtained by combining theoretical with experimental research. A three-dimensional directional wellbore mechanical model is established to analyze the influence of inclination on borehole shrinkage.The salt gypsum layer refers to the formation with salt or gypsum as the main component. In the oil drilling industry, we usually regard the formation as mainly composed of sodium chloride or other water-soluble inorganic salts such as potassium chloride, magnesium chloride, calcium chloride, gypsum, or Glauber’s nitrate as the salt gypsum formation, that is, the salt gypsum layer. According to statistics, salt rocks in sedimentary basins are the best caprock, under which are buried a considerable amount of oil and gas resources in the world, especially rich unconventional oil and gas resources [1-3]. Therefore, the salt gypsum layer is not only the focus of the world oil industry but also the focus of our oil and gas resource development.Along with the process of oil and gas exploitation, the shallow, easily recoverable resources are gradually exhausted, and the exploitation center is gradually transferred to the deep oil and gas resources. The salt rock with very low permeability and porosity is the best caprock, and the drilling of salt rock is unavoidable in the drilling process. The gypsum rocks, which are mainly composed of salt or gypsum, exist above oil and gas reservoirs. The gypsum rocks found in our drilling are mainly distributed in Tarim, Jianghan, Sichuan, Shengli, Zhongyuan, North China, Xinjiang, Qinghai Changqing, and so forth. Various accidents occurred in the drilling of the gypsum rocks in the above oil fields, such as sticking and squeezing casing.Hambley et al. [4] improved the creep constitutive model of salt rock by fully combining the experimental and field data. Fossum et al. [5] determined the stress-related probability distribution function through the pure salt creep test and creep model. Weidinger et al. [6] established a composite plastic deformation model to explicitly consider the heterogeneity of the observed dislocation structure and calculated the transient creep and steady-state creep of salt rock with this model combined with the mechanical laws of dislocation motion. Urai et al. [7] discussed the process of dissolut","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140888535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mеsozoic Tectonothermal Evolution of the Zagan Metamorphic Core Complex in Western Transbaikalia: 40Ar/39Ar and FTA Dating","authors":"Mikhail M. Buslov, Anna V. Kulikova, Evgenii V. Sklyarov, Alexei V. Travin","doi":"10.2113/2024/lithosphere_2023_306","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_306","url":null,"abstract":"A model of tectonothermal evolution of the Zagan metamorphic core complex (MCC) based on the new data from 40Ar/39Ar dating of amphibole, mica, and apatite fission-track dating is discussed. A relationship with the long-range impact of processes from the collision of the North China (Amurian–North China) block with the Siberian continent in the Mesozoic era is proposed. The Zagan MСС was formed in the Cretaceous period on the southern flank of a high mountain uplift of Western Transbaikalia, composed of late Paleozoic granitoids of the Angara–Vitim batholith. According to 40Ar/39Ar dating of amphiboles and micas from the mylonite zone, the active development time of the Zagan MCC corresponds to the early Cretaceous epoch (131, 114 Ma). The tectonic exposure of the core from about 15 km to the depths of about 10 km occurred at a rate of tectonic erosion of 0.4–0.3 mm/year as a result of post-collisional extension of the Mongol–Okhotsk orogen. Apatite fission-track dating shows that further exhumation and cooling of the rocks to about 3 km occurred in the lower-upper Cretaceous epoch (112, 87 Ma). The erosional denudation rate was about 0.3 mm/year.MCC- metamorphic core complexes, AFT- apatite fission-trackMesozoic metamorphic core complexes (MCCs) [1-3] are common in East Asia. They mark global intracontinental extensions along the folded borders of the Siberian craton in Western Transbaikalia and the North China craton [4-13]. The Zagan MCC is one of the more than ten identified ones on the southern border of the Siberian Craton [6-13], where Paleozoic magmatic complexes of the world’s largest Baikal–Vitim and Khentei batholithes and well-known Cenozoic Baikal rift zone occur. Currently, the tectonothermal history of the rocks of the region using apatite fission track dating has been published in a small number of papers [14, 15], partly in [16-19]. In the papers [14, 15], the analysis of geological and geophysical data and the results of track dating revealed the evolution of the relief and tectonic stages of the region formation along the NE-SW profiles from the Baikal-Patom Upland to the Barguzin Ridge, located, respectively, in the northwest and northeast of Lake Baikal. It was assumed, that the Baikal-Patom Upland was reactivated in the middle Jurassic–early Cretaceous epoch after the Mongol-Okhotsk orogeny, occurred in the vast convergence zone of the North Chinese (Amurian–North China block) and Siberian cratons. Apatite fission track dating of the Barguzin Ridge (block) indicates [15] that it intensively rose (rapid cooling phase) in the period of 65–50 Ma (Pliocene-early Eocene epoch) and in the last five Ma (Pliocene-Quaternary period).Tectonothermal evolution of the late Paleozoic granitoids of the Angara–Vitim batholith has been reconstructed using complex thermochronology, including U/Pb, 40Ar/39Ar, and partly fission track dating methods [16-18]. Closure temperatures of the isotope systems of zircon and amphibole show that the rapid","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141190281","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Development of a Large Shaking Table Test for Sand Liquefaction Analysis","authors":"Chuanqin Yao, Huaqiao Zhong, Zhehao Zhu","doi":"10.2113/2024/lithosphere_2024_137","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2024_137","url":null,"abstract":"This article highlights the development of a large shaking table test for sand liquefaction analysis. Two soil containers of different sizes were fabricated. The first one was small (0.87 m × 0.87 m × 1.20 m) in which the reconstitution and saturation methods could be easily tested. The dry tamping (DT) method was used to fabricate a model specimen. The subsequent field measurements suggested that the DT method provided a good distribution of sand grains in different cross sections. Before supplying the model specimen with water, carbon dioxide was flushed to replace air bubbles. This helped in obtaining a good degree of saturation, later verified by a digital moisture meter. For a given inlet water flux, the recorded pore water pressure displayed a quasi-linear trend, suggesting a good internal void system. This reconfirms the effectiveness of the DT method to yield homogeneous model specimens. The second soil container was huge (4 m × 4 m × 2 m) and used to explore liquefaction behavior in real engineering dimensions. Flexible foams were mounted on the side walls to mitigate the boundary effect. Although the boundary effect still manifested itself near the edges of the container during base shaking, half of the model specimen underwent a correct simple shear condition. For further analysis, vane shear tests were carried out before and after the liquefaction test. It was found that the intermediate layer, in general, suffered from the most severe liquefaction failure.Research activities into sand liquefaction have been conducted since the 1964 Niigata earthquake in Japan [1, 2]. In the laboratory, monotonic and cyclic triaxial tests are widely adopted to investigate liquefaction responses. As for laboratory element tests, the state parameter (considering both relative density and consolidation stress [3, 4]) and degree of saturation are two decisive indicators [5, 6] for examining the liquefaction potential. Besides, the soil fabric [7, 8] formed in different specimen reconstitution methods [9-11] has recently been proven to be another influential factor in controlling liquefaction triggering.Although triaxial tests certainly provide valuable insights into the mechanism of sand liquefaction, the understanding based on these tests is still limited by the size effect and thus only represents the liquefaction behavior of a unit soil element. This is far from representing a natural soil extent subjected to seismic loading in a semi-infinite space. Therefore, shaking table tests play an increasingly important role in the context of geotechnical earthquake engineering and contribute to improving the understanding of the liquefaction phenomenon. Many successful configurations have been presented in the literature [12-17]. Teparaksa and Koseki [18] performed a series of liquefaction tests on a shaking table to assess the effect of liquefaction history on liquefaction resistance of level ground. Ko and Chen [19] investigated the evolution of mechanical p","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141503461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantitative Elimination of Seismic Pseudofaults and Fine Analysis of True Faults Underlying Igneous Rocks of No-Well Areas: A Case Study of Shuntuoguole Uplift in Tarim Basin","authors":"Ziran Jiang, Jian Jiao, Qiaomu Qi, Xingyu Deng","doi":"10.2113/2024/lithosphere_2023_129","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_129","url":null,"abstract":"After multistage tectonic movement and evolution, large superimposed oil and gas basins generally developed many igneous rocks in the early rifting stages. The lithology and lithofacies of igneous rocks are complex, which is easy to lead to the distortion of the underlying migration velocity field and thus the response of seismic pseudofaults. Also, because of the obvious shielding and absorption effect of igneous rocks on seismic waves, the waveform quality of underlying strata is poor and the seismic response characteristics of faults are fuzzy. Currently, relevant studies have shown that the influence of igneous rock can be eliminated by the prestack depth migration with an accurate igneous rock velocity model. However, improving the accuracy of the velocity model needs to be corrected by well-logging data, resulting in poor applicability of the existing velocity modeling technology underlying igneous rocks without well, which is an obvious technical bottleneck. In this paper, the secondary strike-slip fault in Shuntuoguole low uplift of Tarim Basin, which has great oil and gas exploration potential but a very low degree of drilling, is selected as the research object. Aiming at difficult fault detection underlying igneous rocks caused by lack of drilling, the accuracy of fault seismic identification is improved by “interpretative fault preprocessing” and “fault sensitive attribute optimization.” In addition, through the “extreme hypothesis method” to maximize the complex migration velocity and simulate the underlying target layer distortion maximization, we realize the quantitative elimination of seismic pseudofaults. The practical application shows that this technology can determine the true and fake underlying faults quantitatively without establishing an accurate igneous rock velocity model. It is crucial not only for exploring oil and gas in the Tarim Basin’s secondary strike-slip faults but also for offering a method and technical guide for identifying faults in other basins affected by igneous rocks.Large superimposed oil and gas basins have undergone multiple periods of tectonic movement and evolution and generally experienced multiple periods of strong magmatic activity in the early stages of rifts or rifts, preserving numerous igneous rocks. As a high-velocity rock mass, igneous rock has two major impacts on the precise structural imaging of its underlying strata [1]. First, igneous rocks strongly shield and absorb seismic waves, leading to the blurring of seismic response characteristics of small structures and faults in the underlying strata. Second, the uneven distribution of thickness, the lateral and vertical variability of lithology, and the significant velocity differences between different lithologies of igneous rock bodies make it difficult to accurately describe the areal distribution, thickness, and velocity of high-velocity igneous rocks before migration imaging. This reduces the accuracy of the migration velocity field a","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141503520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Method for Pressure Relief in Deep Coal Mine Roadways Using Borehole Groups and Its Application to Guqiao Coal Mine","authors":"Yinyu Li, Li Qing, Yongshui Kang, Rui Zhang, Xiang Li, Bin Liu, Zhi Geng","doi":"10.2113/2024/lithosphere_2023_354","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_354","url":null,"abstract":"With the increase in the mining depth of coal mines in China, the problem of large deformation of roadways owing to high-ground pressure has become prominent even under enhanced support systems. To reduce the high pressure on the surrounding rock, this study investigates a pressure-relief method for deep roadways using drilling borehole groups. Based on a deep roadway in the Huainan mining area of China, the influences of drilling parameters, such as borehole diameter, length, and arrangement were investigated. The results indicate that the fan-shaped arrangement of the borehole group can compensate for the dilatancy deformation of the surrounding rock. The peak stress of the surrounding rock is reduced and transferred to the inner part of the surrounding rock. Furthermore, a field experiment was conducted on an experimental roadway. The deformation of the roadway was monitored and compared with that of an adjacent roadway that did not apply the pressure-relief method. The monitoring results indicated that the deformation of the experimental roadway was significantly reduced.In China, coal is a major energy resource, which plays a dominant role in energy systems. China’s coal reserves are approximately 597 trillion tons, out of which approximately 53% are buried in the deep stratum (exceeding the depth of 1000 m) [1-3]. With the increase in the coal mining depth in recent years, an increasing number of roadways suffer from high geo-stress, which induces large deformation and failure and poses serious threats to mining safety [4-6]. Therefore, preventing large deformations of deep roadways with high geo-stress has become an important issue in coal mining. To prevent large deformation problems in deep roadways, engineers usually enhance the support system. For example, the use of high-strength and super-long bolts [6, 7], a method of bolting and shotcreting, U-steel support, grouting and floor bolting casting [3-5], and the reduction of the interval spacing of the supporting structures [4, 5]. Although some development has been achieved, large roadway deformations still frequently occur under high-ground pressure. The resistance offered by the supporting structure is extremely limited. Repeated repair is difficult and results in significant economic losses. Another approach to prevent large deformations of roadways is to release the high-ground pressure around the roadway using special measures. For example, floor grooving releases the high stress that accumulates on the floor, which is conducive to treating floor heaves [7, 8]. The rock mass within the range of pressure relief is destroyed by using high-pressure water injection softening and blasting pressure-relief methods, which reduces the elastic modulus and strength of the rock mass [5-7]. Drilling boreholes [6-9] in coal seams is beneficial for preventing coal and gas outburst accidents. Consequently, the accumulated energy on the surrounding rock surface decreases, leading to the release of","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140829516","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of Rock Fabric on Physical Properties of Shale Oil Reservoir Under Effective Pressure Conditions","authors":"Yu Ma, Suping Yao, Ning Zhu, Huimin Liu, Junliang Li, Weiqing Wang","doi":"10.2113/2024/lithosphere_2023_338","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_338","url":null,"abstract":"The physical properties of shale oil reservoirs under overburden pressure are of great significance for reservoir prediction and evaluation during exploration and development. Based on core, thin section, and SEM observations, as well as test data such as XRD, TOC, and porosity and permeability under pressure conditions, this study systematically analyzes the variation of physical properties of different lithofacies shales in the Jiyang depression and the influence of rock fabric on the physical variation under pressure. The porosity and permeability of shale samples significantly decrease under pressure. According to the phased reduction in porosity and permeability, the pressurization process is divided into three pressure stages: low pressure (<8 MPa), medium pressure (8–15 MPa), and high pressure (>15 MPa). The reduction of porosity is fastest in the low-pressure stage and slowest in the medium-pressure stage. The reduction of permeability is fastest in the low-pressure stage and the slowest in the high-pressure stage. The rock fabric has a significant impact on porosity and permeability under pressure conditions. The permeability of laminated shale and bedded shale is higher than that of massive shale under pressure, and the permeability loss rate is lower than that of massive shales. Especially under lower pressure, the difference can be 10–20 times. In addition, the reduction rate of porosity and permeability under pressure is negatively correlated with felsic minerals content, which is positively correlated with carbonate minerals content and clay minerals content. The contribution of clay minerals to the porosity reduction rate is dominant, followed by carbonate minerals. The contribution of carbonate minerals to the permeability reduction rate is dominant, followed by clay minerals. The TOC content has no significant impact on the porosity and permeability of shales under pressure in the study due to the low maturity.With the change in global energy structure, shale oil and gas has become the core growth point of China’s oil and gas resources [1-4]. In the past decade, a series of important progresses have been made in the exploration and development of shale oil and gas in China, including breakthroughs in the exploration of shale oil in Junggar Basin, Ordos Basin, Jianghan Basin, Songliao Basin, and Bohai Bay Basin [5-8]. However, due to the heterogeneity of shales and the complexity of geological conditions in China, the prediction and evaluation of shale oil reservoirs still face many challenges [3, 9, 10].Many studies have shown that rock fabric, such as laminated structure and mineral composition, has a significant influence on the pore development and physical properties of shale oil reservoirs [10-14]. However, most of these studies were conducted under unpressurized conditions, and there are some errors with the formation conditions, which affect the prediction and evaluation of shale oil desserts. To recover the real physical ","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140932826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimal Inversion Method Based on Joint Waveform Inversion and Least Squares Reverse Time Migration","authors":"Kai Zhang, Yipeng Xu, Zhenchun Li, Zilin He, Yiming Pan","doi":"10.2113/2024/lithosphere_2023_361","DOIUrl":"https://doi.org/10.2113/2024/lithosphere_2023_361","url":null,"abstract":"Joint Waveform inversion (JWI) uses the results of reflection waveform inversion (RWI) as the initial model for full waveform inversion (FWI). Compared with the FWI, the JWI method can obtain more information about the structure of the subsurface medium. The reason is that the reflected waveform inversion can invert the long wavelength component in the middle and deep areas. In JWI, reflected waveform inversion is used to obtain the reflected wave information in the simulation record by demigration, which is computationally more expensive than FWI; the least squares reverse time migration (LSRTM) also obtains the reflected wave information in the simulated record by demigration. In order to effectively use the reflected wave information brought by the high computational amount of reverse migration in JWI, this paper proposes a simultaneous inversion method of JWI and LSRTM (JWI-LSRTM). This method can simultaneously perform an iterative update of the subsurface medium velocity of JWI and the migration imaging of LSRTM, which improves the calculation data utilization rate of each forward and inversion process. In the model test, the effectiveness of the method is proved.Reflected waveform inversion (RWI) is a technique that obtains reflected wave information from simulated records through reverse migration. It can invert long wavelength components in the middle and deep layers [1-3], but its computational cost is higher than full waveform inversion (FWI). FWI is a high-precision inversion method [4-6] with the potential to provide accurate models of subsurface media parameters. Joint waveform inversion (JWI) [7] leverages the results of reflection waveform inversion (RWI) as an initial model for FWI. Compared to FWI, JWI can retrieve more information about the subsurface media structure [8]. This is because RWI can obtain long wavelength components in the middle and deep layers [9, 10]. Ren (2019) proposed an adaptive JWI method that automatically switches between RWI and FWI by adjusting the weight factor with the number of iterations and allowable errors, without manually pausing the switch [11]. This approach addresses the limitations of traditional waveform inversion methods and improves the efficiency and accuracy of subsurface media modeling.The LSRTM [12, 13] is based on the Born approximation, and the reflection coefficient is solved by many iterations with the known background velocity. LSRTM is also used to obtain the reflected wave information from simulated records.In the above three methods, the simulated data and observed data are inverted using the generalized least squares method to obtain the corresponding gradient. However, the computational cost of forward modeling the wave equation and reverse migration is substantial, accounting for at least 90% of the total computation time in these three methods. As a result, the inversion cycle is often prolonged [14, 15]. Now there are a variety of programming techniques (MPI, Openmp, Open","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141253434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Formation of the Great Bend and Enhanced Quaternary Incision of the Upper Yangtze River: New Insights from Low-Temperature Thermochronology and Tributary Morphology","authors":"Yong Zheng, J. Pan, Haibing Li, Yang Wang, Zheng Gong, M. Bai","doi":"10.2113/2023/lithosphere_2023_244","DOIUrl":"https://doi.org/10.2113/2023/lithosphere_2023_244","url":null,"abstract":"\u0000 The occurrence of a sharp turn along the upper course of the Yangtze River is referred to as the “Great Bend” and represents a large-scale drainage reorganization in response to the surface rise of the Tibetan Plateau. However, the timing and mechanism of the formation of the Great Bend remain disputed. In this paper, we report new (U–Th)/He and apatite fission track thermochronological data from the deep river valley in the Great Bend area of the southeastern margin of the Tibetan Plateau. Compared with the adjacent Jianchuan Basin, two phases of younger rapid cooling for the Great Bend area are identified based on thermal-history modeling, namely, Miocene (ca. 17 to 11–8 Ma) and Quaternary, with the former phase being contemporaneous with the formation of the anticline in the Tiger Leaping Gorge. Progressive increases in the normalized channel steepness (ksn) and the degree of river-valley incision with increasing distance downstream for tributaries of the Yangtze River in the Tiger Leaping Gorge indicate that river rerouting and formation of the Great Bend occurred during the Miocene. Samples located at the bottom of the Tiger Leaping Gorge also reveal a phase of rapid cooling since ca. 1.9 Ma, with an exhumation rate of 1.5 ± 0.2 mm/year. We hypothesize that enhanced Quaternary exhumation in the southeastern margin of the Tibetan Plateau occurred mainly within the narrow region between the Sichuan Basin and the Eastern Himalayan Syntaxis, corresponding to an episode of widespread extensional deformation superimposed above middle- to upper-crustal flexure in this region.","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140382972","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cenozoic Exhumation Across the High Plains of Southeastern Colorado from (U-Th)/He Thermochronology","authors":"Sabrina J. Kainz, L. Abbott, R. Flowers, Aidan Olsson, Skye Fernandez, J. Metcalf","doi":"10.2113/2023/lithosphere_2023_310","DOIUrl":"https://doi.org/10.2113/2023/lithosphere_2023_310","url":null,"abstract":"\u0000 Colorado’s High Plains stand at anomalously high elevations (~1300–2100 m) for their continental interior setting, but when and why this region became elevated is poorly understood. The Cenozoic history of the High Plains is also likely linked with that of the Rocky Mountains, where the timing and cause(s) of uplift are similarly debated. We present apatite (U-Th)/He (AHe) data for 10 samples from Tertiary intrusives along a ~200 km west-to-east transect across the High Plains of southeastern Colorado to constrain the timing of exhumation and to gain insight into when and why regional elevation gain occurred. Mean sample AHe dates for the ~24–22 Ma East Spanish Peak pluton and associated radial dikes from the westernmost High Plains are 18.8 ± 1.4 to 14.1 ± 1.7 Ma, recording substantial postemplacement erosion. AHe results for the mafic to ultramafic Apishapa Dikes (oldest ~37 Ma, youngest ~14 Ma) located ~20–40 km farther north and east on the High Plains range from 12.0 ± 1.4 to 6.2 ± 1.9 Ma, documenting continued exhumation on the western High Plains during the ~12–5 Ma deposition of the Ogallala Formation farther east and suggesting that the western limit of Ogallala deposition was east of the Apishapa Dikes. In far southeastern Colorado, the Two Buttes lamprophyre was emplaced at 36.8 ± 0.4 Ma and yields a Late Oligocene AHe date of 27.1 ± 4 Ma. Here, the Ogallala Formation unconformably overlies Two Buttes, indicating that the regional ~12 Ma age for the base of the Ogallala is a minimum age for the exposure of the pluton at the surface. The AHe data presented here document that kilometer-scale erosion affected all of the southeastern Colorado High Plains in Oligo-Miocene time. While exhumation can have multiple possible causes, we favor contemporaneous surface uplift capable of elevating the region to modern heights.","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140088214","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Advancing (U-Th)/He Zircon Dating: Novel Approaches in Sample Preparation and Uncertainty Reduction","authors":"Y. Hao, Ying Wang, Zhuqi Zhang, Jingxing Yu, Yizhou Wang, J. Pang, Wanfeng Zhang, Dewen Zheng","doi":"10.2113/2023/lithosphere_2023_258","DOIUrl":"https://doi.org/10.2113/2023/lithosphere_2023_258","url":null,"abstract":"\u0000 The laser microprobe (U-Th)/He dating method is a new and efficient technique that utilizes an interoperable and integrated suite of instruments, including the excimer laser system, quadrupole helium mass spectrometer, and quadrupole inductively coupled plasma mass spectrometer. To demonstrate the applicability of this new method, we applied both the conventional and laser microprobe techniques to the Sri Lanka zircon (LGC-1). We obtained twenty-two (U-Th)/He ages on nine shards using the laser microprobe method, showing an average (U-Th)/He age of 471.1 ± 16.6 Ma (1σ). This result is generally consistent with the mean conventional age (484.1 ± 9.6 Ma) for twenty-two zircon fragments. Both are nearly equal to the age value (~476 Ma) predicted by the He diffusion model and the thermal history model of Sri Lanka highland. The variations in the laser microprobe-derived ages are most likely caused by the uncertainties in volume measurements, which is also common in other studies. We used the Mahalanobis distance technique to reduce the volume measurement bias by identifying and eliminating abnormal data.","PeriodicalId":18147,"journal":{"name":"Lithosphere","volume":null,"pages":null},"PeriodicalIF":2.4,"publicationDate":"2024-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140449260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}