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Global Geology
2024 Vol.27 Issue.1
Published 2024-02-25
1
Genesis and tectonic setting of Early Jurassic granitic rocks in Huashan Town, Xingcheng, western Liaoning
ZHAO Junfeng,LI Weimin,LIU Tongjun and GAO Jinhui
There are a large number of Mesozoic intrusive and volcanic rocks in western Liaoning of China, which is an ideal place to study the Mesozoic Paleo-Paci?c subduction processes, and lithospheric destruction of North China Craton. Detailed petrographic, zircon U-Pb dating and geochemical studies of the Early Jurassic granites in Huashan pluton, Xingcheng, western Liaoning, indicate that the Early Jurassic granites were formed at 184–174 Ma, mainly composed of syenite and monzogranite. The geochemical characteristics show high contents of SiO2, Al2O3 and Na2O+K2O, low contents of Fe2O3 and MgO, enrichment in LREEs and LILEs, and depletion in HREEs and HFSEs, and have a high content of Sr and low contents of Y and Yb, with weak negative Eu anomalies and slightly negative anomalies of Ce, indicating that they are a set of intermediate-acidic adakitic granites in high-K calc-alkaline series. All the facts signi?cantly suggest that the Early Jurassic adakitic granites were formed at the active continental margin in the context of Paleo-Paci?c plate subduction.
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2024 Vol. 27 (1): 1-19 [
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20
Spatial-temporal distribution and geochemistry of highly evolved Mesozoic granites in Great Xing’an Range, NE China: Discriminant criteria and geological signi?cance
WU Haoran,YANG Hao,GE Wenchun,JI Zheng,DONG Yu,JING Yan and JING Jiahao
Highly evolved granite is an important sign of the mature continent crust and closely associated with deposits of rare metals. In this work, the authors undertake systematically zircon U-Pb ages and whole rock elemental data for highly evolved granitic intrusions from the Great Xing’an Range (GXR), NE China, to elucidate their discriminant criteria, spatial-temporal distribution, di?erentiation and geodynamic mechanism. Geochemical data of these highly evolved granites suggest that high w(SiO2) (>70%) and di?erentiation index (DI>88) could be quanti?ed indicators, while strong Eu depletion, high TE1,3, low ΣREE and low Zr/ Hf, Nb/Ta, K/Rb could only be qualitative indicators. Zircon U-Pb ages suggest that the highly evolved granites in the GXR were mainly formed in Late Mesozoic, which can be divided into two major stages: Late Jurassic–early Early Cretaceous (162–136 Ma, peak at 138 Ma), and late Early Cretaceous (136–106 Ma, peak at 126 Ma). The highly evolved granites are mainly distributed in the central-southern GXR, and display a weakly trend of getting younger from northwest to southeast, meanwhile indicating the metallogenic potential of rare metals within the central GXR. The spatial-temporal distribution, combined with regional geological data, indicates the highly evolved Mesozoic granites in the GXR were emplaced in an extensional environment, of which the Late Jurassic–early Early Cretaceous extension was related to the closure of the Mongol– Okhotsk Ocean and roll-back of the Paleo-Paci?c Plate, while the late Early Cretaceous extension was mainly related to the roll-back of the Paleo-Paci?c Plate.
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2024 Vol. 27 (1): 20-34 [
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35
Numerical simulation of formation mechanism of unloading joints in granitic pluton
JIA Zhenyang,LI Gang and FENG Fan
The Beishan pluton in Gansu of China was selected as the simulated model. The simulation results indicate that the formation of unloading joints in granite is mainly in?uenced by the unloading rate of con?ning pressure. Among the rates tested, the slowest unloading rate 0.025 MPa/s is found to be most conducive to the development of unloading joints. Therefore, a slower unloading rate is favourable for the occurrence of unloading joints. A series of simulations with varying initial depths of uplift ranging from 900 m to 200 m were conducted. The results con?rm that when the specimen rises to a depth of 550–500 m, the unloading joints begin to form. The uplift from a depth of 700–500 m, with variations in both vertical and lateral unloading rates, was simulated. The generation of unloading joints exhibits a negative correlation with vertical unloading and no correlation with lateral unloading, indicating that the unloading joints are mainly controlled by the unloading of vertical pressure. Throughout the simulation process, the vertical joints exhibit irregular and unrealistic regularity, suggesting a more complex formation mechanism than that of the unloading joints.
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2024 Vol. 27 (1): 35-42 [
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Acoustic emission signal identi?cation of di?erent rocks based on SE-1DCNN-BLSTM network model
WANG Weihua and WANG Tingting
In order to study fracture mechanism of rocks in di?erent brittle mineral contents, this study proposes a method to identify the acoustic emission signal released by rock fracture under di?erent brittle mineral content (BMC), and then determine the content of brittle matter in rock. To understand related interference such as the noises in the acoustic emission signals released by the rock mass rupture, a 1DCNN-BLSTM network model with SE module is constructed in this study. The signal data is processed through the 1DCNN and BLSTM networks to fully extract the time-series correlation features of the signals, the non-correlated features of the local space and the weak periodicity law. Furthermore, the processed signals data is input into the fully connected layers. Finally, softmax function is used to accurately identify the acoustic emission signals released by different rocks, and then determine the content of brittle minerals contained in rocks. Through experimental comparison and analysis, 1DCNN-BLSTM model embedded with SE module has good anti-noise performance, and the recognition accuracy can reach more than 90 percent, which is better than the traditional deep network models and provides a new way of thinking for rock acoustic emission research.
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2024 Vol. 27 (1): 43-55 [
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Application of transient Rayleigh wave in detection of tunnel lining void area
ZHENG Chao,WANG Yanlong,ZHANG Baohui and DU Lizhi
Transient Rayleigh wave detection is a high-precision nondestructive detection method. At present, it has been widely used in shallow exploration, but rarely used in tunnel lining quality detection. Through the tunnel lining physical model experiment, the layout defects of the double-layer reinforcement lining area were detected and the Rayleigh wave velocity pro?le and dispersion curve were analyzed after data processing, which ?nally veri?ed the feasibility and accuracy of Rayleigh wave method in detecting the tunnel lining void area. The results show that the method is not a?ected by the reinforcement inside the lining, the shallow detection is less disturbed and the accuracy is higher, and the data will ?uctuate slightly with the deepening of the detection depth. At the same time, this method responds quite accurately to the thickness of the concrete, allowing for the assessment of the tunnel lining’s lack of compactness. This method has high e?ciency, good reliability, and simple data processing, and is suitable for nondestructive detection of internal defects of tunnel lining structure.
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2024 Vol. 27 (1): 56-62 [
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