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Global Geology

	2023 Vol.26 Issue.3 Published 2023-08-25

	133	Zircon U-Pb geochronology, geochemistry and tectonic implication of volcanic rocks from Manketouebo Formation in Keyihe area of northern Great Xing'an Range
		JIA Jinfeng,WANG Yang,LI Pengchuan
		Zircon U-Pb isotope dating and whole-rock geochemical analyses were undertaken for the rhyolite, rhyolitic lithic crystal tuff and dacitic tuff from the Manketouebo Formation in the Keyihe area, in order to constrain their genesis and tectonic significance. Zircon LA-ICP-MS U-Pb data indicate that the rhyolite and rhyolitic lithic crystal tuff were formed during 137±5 Ma and 143±1 Ma，respectively. These volcanic rocks have high SiO2 (70.03%–76.46%) and K2O+Na2O (8.10%–9.52%) contents, but low CaO (0.03%–0.95%) and MgO (0.07%–0.67%) contents, which belong to the peraluminous and high-K calc-alkaline rocks. They are enriched in light rare earth elements (REEs), and exhibit fractionation of light over heavy REEs, with δEu values of 0.37–0.83. The volcanic rocks are enriched in LILEs (e.g., Rb, U and K) and depleted in HFSEs (e.g., Nb, Ti, P and Ta). The chemical composition suggests that these volcanic rocks formed by partial melting of crust material. Combined with previous regional research results, the authors consider that the volcanic rocks of the Manketouebo Formation in the Keyihe area were formed under an extensional environment related to the closure of the Mongolia–Okhotsk Ocean.
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		2023 Vol. 26 (3): 133-145 [Abstract] ( 107 ) [HTML 1KB] [ PDF 768KB] ( 222 )

	146	Logging curves characteristics and response mechanisms of basaltic facies and sub-facies: A case study from eastern sag of Liaohe depression, Northeast China
		YU Xiaojian,QIU Wen,GUO Qiang,FENG Yuhui, WANG Guodong and LENG Qinglei
		Based on five types of conventional logging curves including GR, RLLD, CNL, DEN and AC, and 39 core samples from 30 representative boreholes, the logging characteristics and lithofacies and sub-facies of the basaltic rocks were studied. Three basaltic facies and four sub-facies are recognized from the well logs, including volcanic conduit facies (post intrusive sub-facies), explosive facies, and effusive lava flow facies (tabular flow, compound flow and hyaloclastite sub-facies). The post intrusive, tabular flow and compound flow subfacies logging curves are mainly controlled by the distribution of vesiculate zones and vesiculate content, which are characterized by four curves with good correlation. Post intrusive sub-facies are characterized by high RLLD, high DEN, with a micro-dentate logging curve pattern, abrupt contact relationships at the top and base. Tabular flow sub-facies are characterized by high RLLD, high DEN, with a bell-shaped log curve pattern, abrupt contact at the base and gradational contact at the top. Compound flow sub-facies are characterized by medium-low RLLD, with a micro-dentate or finger-like logging curve pattern, abrupt contact at the base and gradational contact at the top. Explosive facies and hyaloclastite sub-facies logging curves are mainly controlled by the distribution of the size and sorting of rock particles, which can be recognized by four kinds of logging curves with poor correlation. Explosive facies are characterized by low RLLD, medium-low CNL and low DEN, with a micro-dentate logging curve pattern. Hyaloclastite sub-facies are characterized by low RLLD, high CNL, low DEN and high AC, with a micro-dentate logging curve pattern. The present research is beneficial for the prediction of basaltic reservoirs not only in the Liaohe depression but also in the other volcanic-sedimentary basins.
		Guide:
		2023 Vol. 26 (3): 146-156 [Abstract] ( 61 ) [HTML 1KB] [ PDF 755KB] ( 342 )

	157	Determination of multi-component content and construction of digital cores based on CT grey thresholds of altered igneous rocks
		ZHANG Naiyu,GUAN Yao,GUO Yuhang,WANG Qinghui,ZHANG Lihua and PAN Baozhi
		Altered igneous reservoirs have low porosity and permeability, compact structure and certain heterogeneity. A simple digital core with certain generality and multi-parameter constraints can be constructed to characterize the microscopic pore structure and mineral composition. In this paper, based on core X-ray, CT images and whole-rock mineral analysis, threshold segmentation of mass content and grayscale distribution of various minerals in different lithologies of igneous rocks in the buried hill of Huizhou depression is carried out to construct digital core of altered igneous rocks. The results show that after converting the mineral mass content into volume content, the minerals of altered igneous rocks in Huizhou depression can be classified into components. According to the range of grayscale value, components can be divided into six parts. Due to the difference of the content of components in different lithologies of igneous rocks, differentiated grayscale threshold segmentation is needed to obtain the digital core for a single lithology. The final digital core generation process includes two steps: building a single component digital core, and stacking and combining. This kind of universal digital core model can support the subsequent pore scale numerical simulation and comprehensive rock physics research.
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		2023 Vol. 26 (3): 157-166 [Abstract] ( 69 ) [HTML 1KB] [ PDF 596KB] ( 301 )

	167	Comparative study on isolation forest, extended isolation forest and generalized isolation forest in detection of multivariate geochemical anomalies
		ZHENG Chenyi, ZHAO Qingying,FAN Guoyu, ZHAO Keyu and PIAO Taisheng
		It is not easy to construct a model to describe the geochemical background in geochemical anomaly detection due to the complexity of the geological setting. Isolation forest and its improved algorithms can detect geochemical anomalies without modeling the complex geochemical background. These methods can effectively extract multivariate anomalies from large volume of high-dimensional geochemical data with unknown population distribution. To test the performance of these algorithms in the detection of mineralization-related geochemical anomalies, the isolation forest, extended isolation forest and generalized isolation forest models were established to detect multivariate anomalies from the stream sediment survey data collected in the Wulaga area in Heilongjiang Province. The geochemical anomalies detected by the generalized isolation forest model account for 40% of the study area, and contain 100% of the known gold deposits. The geochemical anomalies detected by the isolation forest model account for 20% of the study area, and contain 71% of the known gold deposits. The geochemical anomalies detected by the extended isolation forest algorithm account for 34% of the study area, and contain 100% of the known gold deposits. Therefore, the isolation forest model, extended isolation fo-rest model and generalized isolation forest model are comparable in geochemical anomaly detection.
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		2023 Vol. 26 (3): 167-176 [Abstract] ( 50 ) [HTML 1KB] [ PDF 504KB] ( 425 )

	177	Analysis on advanced transient EM detectability of coal mine roadway
		LING Hong, LIU Yunhe and MA Xinpeng
		The hidden water-bearing structures near the roadway tunnelling face are very likely to cause water seepage accidents in coal mines. Currently, transient electromagnetic (EM) technology has become an important method to detect water damage in advance of roadway excavation. In this paper, the time-domain finite element algorithm based on unstructured tetrahedron grids is used to accurately simulate the geological body in front of the roadway excavation face and analyze its response. The authors detect the distance between the roadway excavation face and the low-resistivity water-bearing body, the resistivity difference between the low-resistivity body and surrounding rock, and the influence of the size of the low-resistivity body on the transient EM response. Furthermore, the common types of low-resistivity bodies in the roadway drivage process are used for modeling to analyze the attenuation of the detected EM response when there are low-resistivity bodies in front of the roadway. The research in this paper can help effectively detecting the water-bearing low-resistivity body in front of the roadway drivage and lay a foundation for reducing the risk of water seepage accidents.
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		2023 Vol. 26 (3): 177-188 [Abstract] ( 50 ) [HTML 1KB] [ PDF 393KB] ( 279 )

	189	Construction land expansion and influencing factors of typical river valley cities in Northeast China: Taking Jilin City as an example
		LI Ruiqi, LI Hong and YIN Jingbo
		Jilin City is a typical river valley city in Northeast China. In this paper, the authors studied the spatial and temporal expansion characteristics of the built-up areas in Jilin City from 1990 to 2020 using the analysis of expansion speed and strength, fractal dimension, barycenter coordinate transfer index and sector analysis. The ultimate-goal is to analyze the driving and restrictive factors that affect the spatial expansion of river valley cities. The results indicate that (1) the expansion speed of urban land in Jilin City has been relatively slow in the past 30 years, while only slightly faster in 2010–2020; (2) in the spatial dimension, Jilin City mainly expanded to the south, then to the west, and extensive expansion has resulted in complex morphology with little stability and compactness; (3) the expansion is affected by multiple factors, of which the positive factor is industrial development, while the restrictive factors include natural factors, population loss, etc. This study provides a case for the formulation of land use policies and land space planning in river valley cities.
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		2023 Vol. 26 (3): 189-198 [Abstract] ( 62 ) [HTML 1KB] [ PDF 542KB] ( 374 )

　

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