25 August 2025, Volume 28 Issue 3

    

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  Constraints on tectonic evolution and mantle source region properties of the Mid-Pacific Mountains: geochemical insights and geological significance

  CHEN Kai, LI Xiaohu, SUN Jiuda1, WANG Zhuoyi, FAN Minghui and LI Xue

  Global Geology. 2025, 28(3): 139-158.

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  This study selects geochemical data of basalts from different seamounts in the Mid-Pacific Mountains province and conducts analyses of major and trace elements as well as Sr-Nd-Pb isotopes to explore the tectonic evolution, petrogenesis, and mantle-source magama characteristics of the Mid-Pacific Mountains. The basalts from the Mid-Pacific Mountains are predominantly alkali basalts, rich in alkalies, and changing in potassium. They exhibit geochemical features of ocean island basalts (OIB), with distinct fractionation between light and heavy rare-earth elements and a pronounced Ce negative anomaly (δCe = 0.16–1.10, average 0.84), along with enrichment in large ion lithophile elements (LILEs). The Mid-Pacific Mountains are intraplate ocean island basalts formed by mantle plume (hotspot) activity, originating mainly from an enriched mantle magma source region, and most of them have undergone low degree of partial melting and a certain degree of crystalline differentiation, with negligible contamination from oceanic crust materials. The Mid-Pacific Mountains exhibit ratios of 87Sr/86Sr(i) (0.702 733–0.704 313, average 0.703 452) and 143Nd/144Nd(i) (0.512 698–0.512 996, average 0.512846) which are close to the HIMU mantle end member, and ratios of 206Pb/204Pb (18.953–19.803), 207Pb/204Pb (15.54–15.62) and 208Pb/204Pb (38.813–39.514) which are close to the EMII mantle end-member. Combined with the isotopic geochemical characteristics in the West Pacific Seamounts province, the basalts from the Mid-Pacific Mountains were considered to represent a certain proportion of mixing mantle end-members between the HIMU and EMII, possibly formed by the mixing of the HIMU superplume in the South Pacific hotspot region with the EMII secondary mantle plume in the transition zone during their ascent.
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  Distribution of fan bodies and effective gas reservoirs in sandstone layer of first member of Yingcheng Formation in Longfengshan Area of Changling Fault Depression

  YAN Xu

  Global Geology. 2025, 28(3): 159-172.

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  The Longfengshan structural belt lies in the southern Changling Depression. The Yingcheng Formation is the primary gas-bearing unit. The Yingcheng Formation has low permeability and contains deep, tight gas that is challenging to extract. Industrial gas flow has been achieved from the B218 and B220 well blocks in the sandstone layer of the first member of Yingcheng Formation (Ying I), indicating the potential of this sandstone group for gas production. Although oil and gas are widely distributed in the Ying I sandstone layer, production capacity varies significantly across the formation. into six sublayers. Drilling, logging, and laboratory testing data were integrated to subdivide the Ying I sandstone layer into six sublayers. Core and well logging analyses indicate a braided river delta depositional environment. Data and seismic inversion identify the Ying I-5 sublayer as the primary exploration target. The effective reservoir in the eastern fan body, where porosity ranges from 5% to 13% and maximum effective thickness reaches 34 m. This study basis for optimizing well placement and estimating gas reserve parameters in the Ying I sandstone layer of the Longfengshan area. The findings can guide the development of other tight gas reservoirs.
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  Analysis of volcanic rock pore structure by high-pressure mercury injection combined with fractal theory

  NIU Penghui and HAN Lei

  Global Geology. 2025, 28(3): 173-185.

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   The pore structure of rocks significantly influences the porosity and permeability of reservoirs and the migration ability of oil and gas, and being the key task on the development of volcanic gas reservoirs. Nine volcanic rock samples from the Yingcheng Formation and Huoshiling Formation in the Longfengshan area of the Changling Fault Depression in the Songliao Basin were selected for this study. The pore structures of the volcanic rocks in the study area were investigated using high-pressure mercury injection, X-ray diffraction combined with fractal theory. The relationships between the fractal dimension and physical properties characteristics, pore structure parameters, and mineral content were analyzed to provide guidance for the development of volcanic rock gas reservoirs. The results show that the reservoir can be divided into 3 types (I, II, and III) based on the shape of the capillary pressure curve, and the physical properties deteriorate successively. Different types of reservoirs exhibit different fractal characteristics. For types I, II and III, the average total fractal dimensions were 2.3418, 2.6850, and 2.9203, respectively. The larger the fractal dimension, the stronger the heterogeneity of reservoir. A small number of macro-pores primarily contributed to permeability. The fractal dimension was negatively correlated with porosity and permeability. The fractal dimension of the rock was strongly correlated with quartz and feldspar contents, and the mineral composition and content are closely related to the pore evolution of the reservoir, which are the internal factors affecting the fractal dimension of volcanic rock.
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  Tempo-spatial distribution and formation mechanism of Recurring Slope Lineae on Mars

  HE Jinxin, YANG Yongbin, YANG Chen, ZHANG Hanya and ZHOU Junhong

  Global Geology. 2025, 28(3): 186-198.

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   Recurring Slope Lineae (RSL) are seasonally observed dark streaks on the Martian surface that exhibit distinct spatial and temporal distribution characteristics. Exploring their formation mechanisms can deepen our understanding of surface activity on Mars and provide scientific basis for future Mars exploration. This study aims to gain a comprehensive understanding of the spatial and temporal distribution characteristics and formation mechanisms of RSL by reviewing relevant literature and synthesizing various viewpoints and experimental results. RSL typically appear during warm seasons, disappear during cold seasons, and repeat over multiple Martian years. The formation mechanisms can be broadly categorized into three types: dry mode, wet mode, and mixed mode. However, a definitive explanation for the formation of RSL is still lacking, and both the dry and wet models have their respective limitations. It is likely that the formation of RSL is the result of the combined action of multiple mechanisms. The next step should be to search for terrestrial analogs of RSL and conduct research at high spatial and temporal resolutions to understand the forming processes of RSL.
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  Monitoring of surface deformation based on SBAS-InSAR in Siping City

  SHI Weiwei, WU Qiong, LI Hongqing, CHI Jiageng and LAN Meixuan

  Global Geology. 2025, 28(3): 199-205.

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  Groundwater overexploitation is the main cause of city surface deformation. In Siping City, groundwater level had decreased since 1980 due to large-scale exploitation of groundwater. Subsequently, the level began to rise under governance while shown a declining trend in the whole Siping area. This paper obtained surface deformation of Siping City from 2017 to 2024 using 36 Sentinel-1B satellite images and 88 Sentinel-1A satellite images based on SBAS-InSAR and analysed the effect of groundwater on deformation. The results indicated that uplift occurs in the centre of the urban area with a maximum average velocity of about 5 mm/y and there were two main subsidence zones during these two time periods with average subsidence velocities of about 3 mm/y and 1.7 mm/y. Groundwater levels showed a high correlation with surface deformation, with rising the levels leading to surface uplift and falling the levels leading to surface subsidence.
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  Sedimentary facies and depositional model of lower member of Dalazi Formation(Lower Cretaceous), Songjiang Basin

  GAO Ningning, ZHENG Xiaoping and SHAN Xuanlong

  Global Geology. 2025, 28(3): 206-216.

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  The lower member of Dalazi Formation is an important oil reservoir in the Songjiang Basin. Based on the research on its field-measured geological profiles, lithological combination characteristics and grain size distribution characteristics, combined with the analysis of the spatial distribution characteristics, sedimentary structural characteristics and hydrodynamic conditions of the sediments in this member, nine sedimentary microfacies of the fan delta plain subfacies, fan delta front subfacies and littoral-shallow lacustrine subfacies have been identified.The study reveals that lower member of Dalazi Formation in the research area follows a fan delta–shallow lacustrine depositional model in the steep slope zone of a rift lake basin. The sediments primarily originate from the Pre-Mesozoic strata in the steep southeastern and eastern margins. The basin center migrated from the early Xiaoshahe area to the Yangmucun–Shenglicun area, and the sedimentary system gradually transitioned from fan delta to littoral-shallow lacustrine facies.