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Global Geology
 
2019 Vol.22 Issue.3
Published 2019-09-25
Articles
Articles
141 Zircon U-Pb geochronology and geochemistry ofgranite in Huoluotai area of northern Great Hinggan Range
CAO Zi'ang, SUN Fengyue, LI Liang, JIA Xiaoyu, LI Jianzhi
Zircon LA-ICP-MS U-Pb geochronology of Huoluotai granite in the studied area shows that the weighted mean age of the rock is 148.12±0.85 Ma, which is of Early Cretaceous. The composition of elementary geochemistry indicates that the granite has high content of SiO2(66.53%-68.92%), K2O+Na2O (8.80%-9.02%) and Al2O3 (15.16%-16.09%), but low MgO (0.72%-0.91%) and Mg# (23.59-29.51). The aluminum saturation index (A/CNK) is 0.87-0.95, with high Sr content of (466.00-688.00)×10-6 and low Y of (4.65-6.22)×10-6. It is indicated that the granite is a set of adakitic rocks with the characteristics of high-K calc-alkaline series. Fraction of light and heavy rare earth elements is obvious, with (La/Yb)N=58.22-117.91, and anomaly of Eu is feeble (δEu=0.83-0.99). The samples are also enriched in light rare earth elements and large ion elements (Rb, K), depleted in heavy earth elements and high field strength elements (Nb,Ti, P, Zr). Combined with the characteristics of regional tectonic evolution, it is suggested that the fine granite originated from the partial melting of the thickened lower crust, which should be related to the collision compression orogeny after the closure of the Mongolia-Okhotsk Ocean.
2019 Vol. 22 (3): 141-151 [Abstract] ( 239 ) [HTML 1KB] [ PDF 1289KB] ( 388 )
152 Slope reliability analysis based on Monte Carlo simulation and sparse grid method
WU Guoxue, PENG Yijin, LIU Xuesong, HU Tao, WU Hao
In order to solve the problem of the reliability of slope engineering due to complex uncertainties, the Monte Carlo simulation method is adopted. Based on the characteristics of sparse grid, an interpolation algorithm, which can be applied to high dimensional problems, is introduced. A surrogate model of high dimensional implicit function is established, which makes Monte Carlo method more adaptable. Finally, a reliability analysis method is proposed to evaluate the reliability of the slope engineering, and is applied in the Sau Mau Ping slope project in Hong Kong. The reliability analysis method has great theoretical and practical significance for engineering quality evaluation and natural disaster assessment.
2019 Vol. 22 (3): 152-158 [Abstract] ( 279 ) [HTML 1KB] [ PDF 434KB] ( 325 )
159 Identification model of geochemical anomaly based on isolation forest algorithm
SHANG Yinmin, LU Laijun, KANG Qiankun
The methods for geochemical anomaly detection are usually based on statistical models, and it needs to assume that the sample population satisfies a specific distribution, which may reduce the performance of geochemical anomaly detection. In this paper, the isolation forest model is used to detect geochemical anomalies and it does not require geochemical data to satisfy a particular distribution. By constructing a tree to traverse the average path length of all data, anomaly scores are used to characterize the anomaly and background fields, and the optimal threshold is selected to identify geochemical anomalies. Taking 1:200 000 geochemical exploration data of Fusong area in Jilin Province, NE China as an example, Fe2O3 and Pb were selected as the indicator elements to identify geochemical anomalies, and the results were compared with traditional statistical methods. The results show that the isolation forest model can effectively identify univariate geochemical anomalies, and the identified anomalies results have significant spatial correlation with known mine locations. Moreover, it can identify both high value anomalies and weak anomalies.
2019 Vol. 22 (3): 159-166 [Abstract] ( 192 ) [HTML 1KB] [ PDF 889KB] ( 371 )
167 Structural mechanism and construction method of mud and water inrush in Xiangyun tunnel of Guangtong-Dali railway
WANG Yawei
Mud and water inrush in tunnel is a common problem in the construction process. Nowadays, the research and classification on this are mostly focused on karst situations. According to the characteristics of the surrounding rock and damage forms of the tunnel in the studied area, the author analyzed the geological and structural characteristics of mud and water inrush in tunnel and obtained their construction type. Meanwhile, the advanced water detection under the complex geological conditions was studied by using induced polarization method, transient electromagnetic method and three-dimensional seismic method, it can be concluded that the water-rich fracture zone exists within the detection range with a risk of large mud and water inrush disaster. The concrete construction treatment measures are put forward:①cement-water glass binary slurry is selected as the material for ground and hole grouting, its advantage is that the gel time can be controlled, and it has certain grout ability in the strata with large permeability coeffcient, which is conducive to excavate construction immediately after grouting. ②applying the mature retrograde grouting construction can reduce grouting time and improve the excavation efficiency.
2019 Vol. 22 (3): 167-178 [Abstract] ( 197 ) [HTML 1KB] [ PDF 1718KB] ( 323 )
179 Regularized focusing inversion for large-scale gravity data based on GPU parallel computing
WANG Haoran, DING Yidan, LI Feida, LI Jing
Processing large-scale 3-D gravity data is an important topic in geophysics field. Many existing inversion methods lack the competence of processing massive data and practical application capacity. This study proposes the application of GPU parallel processing technology to the focusing inversion method, aiming at improving the inversion accuracy while speeding up calculation and reducing the memory consumption, thus obtaining the fast and reliable inversion results for large complex model. In this paper, equivalent storage of geometric trellis is used to calculate the sensitivity matrix, and the inversion is based on GPU parallel computing technology. The parallel computing program that is optimized by reducing data transfer, access restrictions and instruction restrictions as well as latency hiding greatly reduces the memory usage, speeds up the calculation, and makes the fast inversion of large models possible. By comparing and analyzing the computing speed of traditional single thread CPU method and CUDA-based GPU parallel technology, the excellent acceleration performance of GPU parallel computing is verified, which provides ideas for practical application of some theoretical inversion methods restricted by computing speed and computer memory. The model test verifies that the focusing inversion method can overcome the problem of severe skin effect and ambiguity of geological body boundary. Moreover, the increase of the model cells and inversion data can more clearly depict the boundary position of the abnormal body and delineate its specific shape.
2019 Vol. 22 (3): 179-187 [Abstract] ( 235 ) [HTML 1KB] [ PDF 1026KB] ( 415 )
188 Pre-stack seismic waveform inversion based on adaptive genetic algorithm
LIU Sixiu, WANG Deli, HU Bin
Pre-stack waveform inversion, by inverting seismic information, can estimate subsurface elastic properties for reservoir characterization, thus effectively guiding exploration. In recent years, nonlinear inversion methods, such as standard genetic algorithm, have been extensively adopted in seismic inversion due to its simplicity, versatility, and robustness. However, standard genetic algorithms have some shortcomings, such as slow convergence rate and easiness to fall into local optimum. In order to overcome these problems, the authors present a new adaptive genetic algorithm for seismic inversion, in which the selection adopts regional equilibrium and elite retention strategies are adopted, and adaptive operators are used in the crossover and mutation to implement local search. After applying this method to pre-stack seismic data, it is found that higher quality inversion results can be achieved within reasonable running time.
2019 Vol. 22 (3): 188-198 [Abstract] ( 191 ) [HTML 1KB] [ PDF 1161KB] ( 532 )
199 Mode decomposition methods and their application in ground penetrating radar data processing
ZHOU Weifan, ZENG Zhaofa, LI Jing
Ground Penetrating Radar (GPR) method is a widely used method in engineering geophysical exploration at home and abroad. Compared with other geological exploration methods, the GPR method has the advantages of faster detection, higher resolution, convenient operation and relatively low detection cost. With the wide application and continuous development of GPR methods, the processing and interpretation of GPR data is increasingly important. The authors introduce the development process and current situation of the modal decomposition method in processing GPR data, summarize the principles of four modal decomposition methods, and compare their advantages and disadvantages in ground penetrating radar data processing. The results show that when the quality of GPR data is good and the noise is small, Empirical Mode Decomposition (EMD) and Ensemble Empirical Mode Decomposition (EEMD) methods can be used for processing, whereas when the noise interference is large or the underground medium is complex, Complete Ensemble Empirical Mode Decomposition (CEEMD) and Variational Mode Decomposition (VMD) methods can be used for processing. The four modal decomposition methods have their own advantages and disadvantages in GPR data processing. At present, the processing of GPR data by CEEMD and VMD methods is the focus of research and discussion at home and abroad.
2019 Vol. 22 (3): 199-208 [Abstract] ( 245 ) [HTML 1KB] [ PDF 1585KB] ( 340 )
209 Logging interpretation method for reservoirs with complex pore structure in Mesozoic-Cenozoic faulted basin around Daqing exploration area
YUE Shanshan, FAN Xiaomin, HUANG Buzhou
In Mesozoic-Cenozoic faulted basin in the periphery of Daqing exploration area, the clastic reservoirs mainly consist of siltstone and gravel-bearing sandstone. The electrical conductivity of the reservoirs is complicated due to the complex pore structures, which cannot be accurately interpreted with commonly used model. In order to solve the problem, a three-water model has been applied in this study based on in-depth analysis of the conductive mechanism of rocks in the explored area, and favorable application results are achieved.
2019 Vol. 22 (3): 209-216 [Abstract] ( 243 ) [HTML 1KB] [ PDF 961KB] ( 334 )
　

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