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Global Geology

	2024 Vol.27 Issue.4 Published 2024-11-25

	177	Geochronology and geochemistry of Daerlong granitic complex in Linkou area, eastern Heilongjiang: petrogenesis and tectonic implications
		QIN Tao,FANG Jie,ZHANG Yanlong,DING Xin,YU Guanying and YANG Hao
		The Daerlong granitic complex in Linkou area is located at the convergence position of the Jiamusi and Songliao blocks. A systematic study of field geology, petrography, zircon U-Pb dating and wholerock major and trace elements has been conducted for the Daerlong granitic complex, aiming to determine its formation age, petrogenesis and tectonic setting, and further constrain the nature and evolution of the Mudanjiang Ocean. Field and petrographic observations show that the Daerlong granitic complex mainly consists of three rock types from old to young, i.e., biotite granodiorite, syenogranite and monzogranite. Geochemical data suggest that all the types of granitoids are high in silicon, rich in potassium, moderate in aluminum (A/CNK=0.94–1.10), poor in iron and magnesium, rich in LILEs and depleted in HFSEs, belonging to the weakly peraluminous high-K calc-alkaline series. Combined with mineral assemblages and geochemical discrimination diagrams, it can be determined that the studied granitoids are of igneous crustderived I-type origin, which underwent strong fractional crystallization and crystal accumulation during magmatic evolution. Zircon LA-ICP-MS U-Pb dating results show that the different types of granitoids were emplaced in a wide age range from 301 to 240 Ma, indicating a long-lived Late Carboniferous to Middle Triassic granitic magmatism occurred in the western Jiamusi Block. The Daerlong granitoids have similar geochemical characteristics of subduction-related igneous rocks. Considering the spatial and temporal distribution of Late Paleozoic to Early Mesozoic igneous rocks within eastern Heilongjiang Province, it is concluded that the Daerlong granitic complex was formed in an active continental margin setting rather than a continental rift environment. The results suggest that the Mudanjiang Ocean might not be a limited ocean evolved from the rifting of the uniffed Jiamusi-Songnen microcontinent.
		Guide:
		2024 Vol. 27 (4): 177-195 [Abstract] ( 17 ) [HTML 1KB] [ PDF 1070KB] ( 92 )

	196	Research on rock hand specimen naming method based on deep learning and Inception-v3 model
		LI SiJia,SHEN YanJie and QIAN Ye
		The naming of rock hand specimens is usually conducted by geological workers based on observed mineral composition, texture characteristics, etc., combined with their own knowledge reserves. The accuracy of identiffcation results is limited by the experience, research interests, and identiffcation level of the identiffer, as well as the complexity of the rock composition. To improve the efffciency of rock hand specimen identification, this paper proposes a method for rock image recognition and classification based on deep learning and the Inception-v3 model. It encompasses the preprocessing of collected photographs of typical intrusive rock hand specimens, along with augmenting the sample size through data augmentation methods, culminating in a comprehensive dataset comprising 12501 samples. Experimental results show that the model has good learning ability when there is sufffcient data. Through iterative training of the Inception-v3 model on the rock dataset, the accuracy of rock image recognition reaches 92.83%, with a loss of only 0.2156. Currently, several common types of intrusive rocks can be identified: gabbro, granite, diorite, peridotite, granodiorite, diabase, and granite porphyry. Software is developed for open use by geological workers to improve work efffciency.
		Guide:
		2024 Vol. 27 (4): 196-206 [Abstract] ( 20 ) [HTML 1KB] [ PDF 547KB] ( 80 )

	207	Geoid interpolation in Gongzhuling City and the 1cm quasi geoid reffnement
		WANG Yongchun,ZHONG Linshan,ZHAO Han and WU Qiong
		The reffnement of the 1cm geoid holds signiffcant importance in engineering applications, where the accuracy of the geoid is frequently constrained by its resolution. However, there has been limited exploration into the speciffc relationship between geoid resolution and accuracy. This article aims to address this gap by thoroughly examining said relationship. This study employs the CapRCR modification to calculate the geoid of Gongzhuling City. The ffndings indicate that the accuracy can be enhanced by 2% to 9% through encryption of the geoid resolution from 2.5′×2.5′ to 1.5′×1.5′. Furthermore, this improvement can be augmented by 15% to 21% through encryption of the gravity anomaly to the same resolution. The accuracy of the geoid exhibits a linear relationship with the resolution of gravity anomalies. The theoretical accuracy of the geoid, excluding integration errors, is determined to be 1.21 cm. In engineering applications, opting for a resolution of 30''×30'' can result in the geoid containing only an integration error of 2 mm. However, to attain an accuracy of 1 cm, it becomes imperative to further mitigate data errors. Consequently, the ffnal reffned quasi-geoid accuracy is established at 0.56 mm.
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		2024 Vol. 27 (4): 207-215 [Abstract] ( 27 ) [HTML 1KB] [ PDF 322KB] ( 104 )

	216	3D time-domain forward modeling of airborne transient electromagnetism considering superparamagnetic effect
		LI Zizhuo, LIU Yunhe* and REN Xiuyan
		The superparamagnetic effect arises from the superparamagnetism exhibited by a multitude of nano-sized magnetic mineral particles under an external electric ffeld. This phenomenon manifests in transient electromagnetic data primarily as a deceleration in the attenuation rate of late-stage signals, a characteristic difffcult to discern directly from airborne transient electromagnetic signals, consequently leading to signiffcant misinterpretations of subterranean electrical structures. This study embarks on 3D forward modeling of airborne electromagnetic responses in the frequency domain, accounting for the superparamagnetic effect, utilizing an unstructured finite element method. Superparamagnetic responses in the time domain were obtained through frequency-time conversion. This investigation explores the influence of various parameters—such as magnetic susceptibility, time constants, and ffight altitude—on the superparamagnetic effect by examining the response characteristics of typical targets. Findings indicate that in its late stages, the superparamagnetic effect can induce a relative anomaly of up to 300%. There is a positive correlation between magnetic susceptibility and the strength of the superparamagnetic effect. The inffuence of the time constant's upper and lower limits on the superparamagnetic effect is minimal; however, the range between these limits significantly affects the effect, showing a negative correlation with its intensity. Higher flight altitudes weaken the superparamagnetic signal. The impact is most pronounced when superparamagnetic minerals are shallowly buried, effectively shielding the underlying geology with the characteristics of a good conductivity anomaly, but this effect diminishes with greater depth. The insights from this study provide a theoretical framework for a deeper understanding of the superparamagnetic effect in transient electromagnetic signals and for more accurate interpretations of subterranean geological and electrical structures.
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		2024 Vol. 27 (4): 216-232 [Abstract] ( 26 ) [HTML 1KB] [ PDF 753KB] ( 78 )

　

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