Current Issue

2024, Volume 35,  Issue 1

2024, 35(1)
2024, 35(1)
Geochemistry and Mineral Deposits
Trace Element Mobility in Subducted Marble and Associated Eclogite: Constraints from UHP Rocks in the Shuanghe Area, Central-East China
Xingao Hou, Zhiqiang Yu, Shefa Chen, Lei Liu, Yilin Xiao
2024, 35(1): 1-15. doi: 10.1007/s12583-022-1692-3

In order to decipher element mobility in UHP meta-sedimentary rocks in the continental subduction zone, major and trace element compositions are investigated for a continuous profile from a representative UHP region in the Dabie Mountains. Among the lithologic contact zone, contents of K, Ca, LREE, and LILE exhibit varying degrees of downward trends in both marble and eclogite toward the contact zone, indicating that marble and their associated eclogite can release a large amount of K, Ca, and a small number of LILEs and LREEs. Titanite is the main Ti phase in both marble and eclogite. Titanite rims around rutile can occasionally be seen in eclogite. Contents of Ti and HFSE exhibit a well-coupled relation among marble and eclogite, indicating that substantial Ti and HFSEs were migrated from eclogite to marble, in accord with the capacity of a melt medium. Rutiles and titanites in marble exhibit a relatively limited variation in Nb/Ta ratios (12.9–16.2), similar to those of titanites in eclogite (14.2–16.7), which demonstrates that rutiles and titanites in marble were sourced from eclogite because of short-distance migrations of Ti and HFSEs. According to the P-T path and the temperature and pressure conditions of the peak metamorphism reported by previous studies, the eclogite associated with marble may not form supercritical fluids in the subduction zone because of the addition of carbonate minerals.

Insight into the Origin of Iron Ore Based on Elemental Contents of Magnetite and Whole-Rock Geochemistry: A Case of the Bipindi Banded Iron Formations, Nyong Complex, SW Cameroon
Landry Soh Tamehe, Huan Li, Sylvestre Ganno, Zuxing Chen, Yanick Brice Lemdjou, Safiyanu Muhammad Elatikpo
2024, 35(1): 16-28. doi: 10.1007/s12583-022-1622-4

The Bipindi iron ore district is located in the central section of the Nyong Complex at the northwestern margin of the Congo Craton in Southwest Cameroon. This iron district contains numerous iron mineralization hosted by the Mewongo, Bibole, Kouambo, and Zambi banded iron formations (BIFs). These BIFs contain magnetite as the main iron ore mineral associated with pyrite, and gangue minerals are quartz with minor chlorite and amphibole. The origin of iron ore from these BIFs was investigated using a combination of in-situ magnetite and whole-rock chemistry. The studied BIF ore samples have a narrow range of TFe between 30.90 wt.% and 43.20 wt.%, indicating a low-grade ore. The geochemical signatures of magnetite such as low contents of base metals (e.g., Cu, Co, V, and Zn) and low Co/Zn ratios < 0.85 indicate a hydrothermal origin. Combined with the geochemical features of these BIFs, e.g., high Fe/Ti and Fe/Al ratios (mean > 600 and > 75, respectively), we suggest that magnetite was derived from a mixture of seawater and ~0.1% low-temperature hydrothermal fluids in an oxidizing environment. Collectively, low-temperature hydrothermal and later metamorphic fluids were necessary for the transformation of the protolith Nyong Complex BIFs to iron ore.

A Deep Mantle Source for the Late Neoarchean Metamorphosed Basalts in Eastern Hebei, North China Craton: Insights from Whole-Rock Geochemistry and Sm-Nd Isotopes, and Zircon U-Pb-Hf Isotopes
Zhuang Li, Chunjing Wei, Chuan Yang, Xi Zhang
2024, 35(1): 29-40. doi: 10.1007/s12583-023-1807-5

The basalts within the greenstone belt worldwide serve as an ideal target to decipher the nature of Archean mantle sources and further to extend the understanding of the early stages of Earth's evolution. To provide important insights into the issues, we carried out a detailed investigation of whole-rock geochemistry and Sm-Nd isotopes, and zircon U-Pb-Hf isotopes for the Late Neoarchean metamorphosed basalts in eastern Hebei, North China Craton. U-Pb isotopic dating using the LA-ICP-MS on zircons reveals that the basalts in eastern Hebei erupted at ca. 2.48–2.51 Ga and subsequently experienced multiple regional metamorphic events at 2 477 and 1 798 Ma, respectively. The metamorphosed basalts are featured by low SiO2, MgO, K2O + Na2O, and high FeO contents, endowed with the subalkaline and high-Fe tholeiitic affinities. The radiogenic initial Nd and Hf isotope values and correlations among V, Ni and Cr contents strongly imply that the basalts experienced significant clinopyroxene and olivine fractionation and minor crustal contamination during magma evolution. They are also characterized by the relatively low total REE contents and exhibit significant depletions to moderate enrichments in the LREE contents, indicating the derivation from a deep mantle source in an Archean proto-mantle plume setting.

Zircon Hf Isotope Mapping for Understanding Crustal Architecture and Its Controls on Mineralization during Early Cretaceous in the Southern Great Xing'an Range, NE China
Feng Yuan, Huanan Liu, Shengjin Zhao, Mingjing Fan
2024, 35(1): 41-50. doi: 10.1007/s12583-020-1100-9

Voluminous Early Cretaceous granitoids and associated large-scale ore deposits are distributed within the southern Great Xing'an Range (SGXR), NE China. Based on previously published geochronology and zircon Hf-isotope data, Hf isotope mapping is undertaken to improve our understanding of crustal architecture and its controls on ore deposits. The ore-related Early Cretaceous granitoids were sourced predominantly from juvenile crust, with the involvement of variable proportions of ancient crustal materials. The crustal architecture, as inferred from Hf isotopic contour maps, indicates two distinct Hf isotopic domains in SGXR, including (1) a higher-εHf (+7 to +11) juvenile crust containing minor ancient crustal material, and (2) a lower-εHf (+2 to +6) juvenile crust containing a greater proportion of ancient crustal materials.The Hf isotopic maps identify links between crustal architecture and regional metallogeny. Copper deposits and other deposits with significant Cu production are restricted mainly to the higher-εHf juvenile crustal regions in the northern and eastern SGXR. Deposits dominated by other metals (e.g., Mo, Sn, W, Pb, Zn, and Ag) occur mainly in the lower-εHf juvenile crustal regions in the southern and western SGXR. Interaction between juvenile crust-derived melts and ancient crustal components played an important role on the distribution of various ore metals.

Geochemical Characteristics and Development Significances of Constant and Trace Elements from Coalbed Methane Co-Produced Water: A Case Study of the Shizhuangnan Block, the Southern Qinshui Basin
Yang Li, Shuheng Tang, Jian Chen, Songhang Zhang, Zhaodong Xi
2024, 35(1): 51-61. doi: 10.1007/s12583-022-1628-y

As an unconventional natural gas resource, coalbed methane (CBM) development releases a large amount of CBM wells co-produced water. Geochemical characteristics of the co-produced water provide an essential foundation for the production dynamics of CBM reservoirs if the impacts of fracturing fluids and other aquifers can be ignored. In the Shizhuangnan Block of the southern Qinshui Basin, constant and trace elements in CBM co-produced water from the wellheads were collected and determined, which is applied to assess water source, fracturing fluid effect, and CBM production. Based on principle component analysis and hierarchical clustering analysis, the water samples are divided into four categories. It suggests that different characteristics affected by water-rock interaction, reservoir environment, aquifer recharge, and hydraulic fracturing result in the various ratios of Na+/Cl-, alkalinity (HCO3- + CO32-)/Cl- and other specific rules. Moreover, Cl- is selected as a dividing line for complete fracturing fluid flow back, associated with organic-bound chlorine complexes in the original coal seam water. Compared to constant elements, there is a significant correlation between Li and Sr concentrations and CBM productivity, so templates regarding trace elements can be used to distinguish various sources of the co-produced water.

Characterization of Arroyo Verde Epithermal Deposit: Paragenesis, Mineral Geochemistry, Geochronology and Fluid Inclusions in Lower Chon Aike Volcanism, Argentina
Cecilia Pavón Pivetta, Leonardo Benedini, Paulo Marcos, Ma. Agustina Cócola, Mercedes Virginia Barros, Daniel Gregori, Leonardo Strazzere, Anderson Costa dos Santos, Mauro C. Geraldes
2024, 35(1): 62-84. doi: 10.1007/s12583-023-1823-5

Arroyo Verde epithermal deposit, in the North Patagonia region of Argentina, is located within the Lower Chon Aike volcanism and is developed between 192.6 ± 2.5 Ma (mineralization host rock) and 189.5 ± 2.6 Ma (overlying lava). Marifil volcanic complex is the host rock for these veins, veinlets and breccias. This particular small deposit has developed low to intermediate sulphidation characteristics, with gangue mineral textures associated with several ore minerals. Electron probe microanalysis determines electrum, silver minerals such as acanthite, and tetrahedrite, related Ag-Cu minerals like jalpaite, mckinstryite, stromeyerite, and base metals like chalcopyrite, sphalerite, galena and pyrite. Fluid inclusions in quartz of two out of five events indicate that these Low Jurassic veins were formed due to subtle boiling and dilution mechanisms and by low-salinity (3.4 wt.% to 6.7 wt.% NaCl Eq) magmatic-hydrothermal fluid at 225 to 310 ℃. The fluid inclusion measurements that indicate boiling (Event 3) were plotted, and based on this data, we interpret that the Arroyo Verde deposit has been eroded between 550 and 700 m. This particular character has not been previously recorded for other sectors of the eastern north Patagonian region.

Structural Geology
SS-LASS Zircon Dating Deciphering Multiple Episodes of Anatexis in a Deeply-Subducted Continental Crust: An Example from Sulu Orogen, China
Peng Feng, Lu Wang, Xiawen Li, Wenjie Ding, Zhe Chen
2024, 35(1): 85-98. doi: 10.1007/s12583-022-1797-8

'Single shot' laser-ablation split-stream (SS-LASS) technique analyzing unpolished zircon grains makes their thin rims tenable for determination, which thus offers great potential in deciphering the timing of multiple and short-lived episodes of anatexis and metamorphism in deeply-subducted continental crusts. Dominated granitic gneisses in the deeply subducted continental crust undergoing considerable fluid-melt activities persist multistage growth of zircon. Therefore, a comparative study of SS-LASS and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) zircon dating was conducted on the granitic gneisses from the Sulu belt in this study. Zircons mostly show a core-mantle-rim structure with CL-bright rims thinner than 5 μm. For LA-ICP-MS dating, relict magmatic zircon cores yield protolith ages of ca. 756–747 Ma; whereas the dark mantles record syn-exhumation anatexis at ca. 214 Ma. By contrast, according to the U-Pb dates, trace element features, zircon crystallization temperatures and geological context, SS-LASS zircon petrochronology deciphers three episodes of anatectic events, as follows: (ⅰ) the first episode of anatexis at ca. 218–217 Ma dominated by phengite-breakdown melting, likely facilitating the exhumation of the UHP slice from mantle depth; (ⅱ) the second episode of anatexis at ca. 193–191 Ma indicating part of northern Dabie-Sulu belt was still "hot" because of buried in the thickened orogenic crust at that time; (ⅲ) the third episode of anatexis (ca. 162–161 Ma) consistent with the intrusion ages (ca. 161–141 Ma) of the Jurassic to Cretaceous granitoids in this orogen, suggesting the initial collapse of the orogenic root of the Sulu belt occurred at Late Jurassic due to the Izanagi plate initially subducting beneath the margin of Eastern Asia. This study sheds new light upon the utilization of SS-LASS petrochronology deciphering multiple anatectic events in the deeply-subducted continental crust and supports us in better understanding the tectonic evolution of Dabie-Sulu Orogen.

Cretaceous–Neogene Exhumation of the Daqing Shan, North China Constrained by Apatite Fission Track Thermochronology
Junlin Zhou, Yuhong Li, Wei Han, Yunpeng Zhang, Gaochao Chen, Qiao Zhang, Jianshe Wei, Yazhuo Niu
2024, 35(1): 99-111. doi: 10.1007/s12583-021-1518-8

The Daqing Shan (DQS) located in the Yinshan-Yanshan Orogenic Belt plays an important role in the Mesozoic to Cenozoic evolution of the North China Craton. However, the cooling and exhumation history since the Cretaceous is still controversial. Integrating the apatite fission track (AFT) data in both this study and previous works, a three-stage exhumation history from Cretaceous to Neogene of the DQS is proposed. (1) The first stage is composed of the early exhumation during Early Cretaceous driven by the collision between the North China and Siberia cratons (ca. 148–132 Ma) and the far-field effect of the subduction of the Pacific Plate (ca. 132–114 Ma). (2) Due to the subsidence of the Hetao Basin and the subsequent compensation between the DQS and the Hetao Basin, the DQS experienced the second rapid exhumation from Early Eocene to Early Oligocene (ca. 54–29 Ma). (3) Since the Late Miocene (ca. 13.5 Ma), the third rapid cooling and exhumation of the DQS occurred due to the far-field effect of the uplift of the Tibetan Plateau and the subduction of the Pacific Plate.

Formation of the Tibetan Plateau during the India-Eurasia Convergence: Insight from 3-D Multi-Terrane Thermomechanical Modeling
Jile Chen, Peimin Zhu, Yuefeng Yuan, Guifan Chen
2024, 35(1): 112-130. doi: 10.1007/s12583-023-1931-0

Various models exist to explain the formation of the Tibetan Plateau, including "tectonic escape", "pure shear thickening", "convective removal of the lithospheric mantle", and "lower crustal flow" model. The first two models are primarily constructed on pure mechanical models but are unable to reasonably explain the tension and shear phenomena inside the plateau. The latter two are rheological dynamic models based on deep geophysical observations. However, the spatial range of the lower crustal flow and its role in the plateau formation/uplift remain controversial. Five multi-terrane visco-plastic thermomechanical models were constructed to simulate the uplift and lithospheric structure change of the Tibetan Plateau during the post-collision stage (since 35 Ma) under the convergence of the Indian Plate. Results show that the plateau's formation begins with crustal thickening, blocked by strong terranes at the northern plateau, and expanded laterally to the east. The lithosphere thickens gradually and experiences delamination at its base, elevating temperature within the crust and forming partial melting layers in the central plateau. As convergence persists on the southern side, the northern plateau's lithosphere bends downward and undergoes delamination, further heating the crust and promoting the northward and eastward flow of partial melting layers, leading to secondary uplift around the plateau.

Evaluation of the Relative Tectonic Activity from the Faults in the Gengma-Lancang-Menghai Seismic Belt (Southwestern China)
Dan Wang, Youpu Dong, Zhipeng Xi, Dongyue Zhang, Jiaxin Duan, Huayu Yu, Liang Yu
2024, 35(1): 131-143. doi: 10.1007/s12583-021-1565-1

The Gengma-Lancang-Menghai seismic belt, the southernmost part of the North-South seismic belt, is controlled by four active faults: the Nantinghe fault (NTHF), the Sanjianshan fault (SJSF), the Hanmuba-Lancang fault (HMB-LCF), and the Heihe fault (HHF), from northwest to southeast. However, the tectonic activity of the faults in the Gengma-Lancang-Menghai seismic belt has not been fully studied yet. In the present work, we conducted tectonic geomorphic indices to analyze the relative tectonic activity along the faults in the seismic belt based on the digital elevation model. We interpreted asymmetric factor, index of drainage basin shape, hypsometric integral, normalized stream-length gradient, valley floor-to-width to height ratio, and longitudinal profiles to show that the relative tectonic activity is higher in the north and lower in the south, and is strong in the region from Shanjia to Huimin in the center of the seismic belt.

Hydrogeology and Environmental Geology
Characteristics of Paleontological Communities in Surface Sediments of the Southern South China Sea and Their Paleoclimatic and Paleoenvironmental Significance
Jing Zhao, Li Zhang, Xiaoyan Wang, Jinglian Ge, Min Xu, Wei Chen, Mao Luo, Qianyong Liang, Qiuhua Yu, Shuaibing Luo, Wenkun Qie
2024, 35(1): 144-154. doi: 10.1007/s12583-023-1910-5

Understanding the spatial and temporal distribution of different paleontological communities in the southern South China Sea (SCS) is fundamental to explore its paleoclimatic and paleoenvironmental changes. In this study, foraminifera, pollen and diatoms from 100 surface sediment samples covering 40 000 km2 of sea floor in the southern SCS were comprehensively investigated in terms of their assemblage and distribution. The results showed the existence of abundant foraminifera and pollen in most of the samples, although diatom communities were relatively scarce. Foraminifera were dominated by G. sacculifer, G. menardii, G. ruber, while diatoms were characterized by T. simonsenii, T. nitzschioides and T. longissima, indicating a typical tropical marine environment. The pollen assemblages showed a better reflection of montane rainforest, tropical rainforest and mangrove. The spatial differences among foraminifera assemblages may indicate the effect of water depth and a warmer environment in the southeast part of the study area, while the spatial patterns of diatom and pollen assemblages imply the influence of coastal current. Our study also noted that the compositions of paleontological communities in the SCS can vary significantly in a short distance, and synthesized studies on multiple biological groups are needed to reconstruct the Quaternary climate and the oceanographic environment.

Hydrochemical Characterization, Controlling Factors and Water Quality of Surface Water in Shandong Province, North China
Ran An, Jiutan Liu, Zongjun Gao, Changsuo Li, Yuming Peng
2024, 35(1): 155-166. doi: 10.1007/s12583-021-1441-z

In this study, 90 surface water samples were collected from Shandong Province (SDP) in the dry and wet seasons and analyzed using statistical analysis, hydrochemical methods and water quality index (WQI). The content of main ions showed seasonal variations, with a higher average value in the dry season than in the wet season. Sampling points exhibiting high contents of the main chemical components were mainly distributed in areas southwest of SDP, north of Weifang, and around Jinan. The saturation index of carbonate minerals was greater than zero, while that of evaporite minerals was less than zero. The hydrochemical characteristics of surface water are mainly dominated by rock weathering as well as cation exchange. In addition, surface water in SDP has significantly been affected by anthropogenic factors. Most of the surface water could be classified as weakly alkaline soft-fresh water, with the hydrochemical types of SO4·Cl-Ca·Mg and SO4·Cl-Na. In terms of WQI, 47.88% and 37.88% of the water samples in SDP were classified as poor water in the dry and wet seasons, respectively. On the whole, the water quality is higher in the wet season than in the dry season, and surface water in SDP is generally suitable for agricultural irrigation.

A Novel Gymnosperm Wood from the Lopingian (Late Permian) in Zhangzi, Shanxi, North China and Its Paleoecological and Paleogeographic Implications
Xiao Shi, Jianxin Yu, Yuewu Sun, Zhen Xu, Hui Li
2024, 35(1): 167-176. doi: 10.1007/s12583-021-1510-3

The Permian-Triassic transition saw extreme climatic changes that severely impacted the terrestrial ecosystem. Fossil plants, particularly fossil woods, are sensitive to climatic changes, and they, therefore, are unique materials revealing extreme environmental and climatic changes on land at that time. Abundant conifer woods were discovered in the Lopingian (Late Permian) strata of the Sunjiagou Formation in Shanxi Province, North China. The newly finding permineralized woods record the unique landscape of Lopingian North China. They represent a new conifer genus and species: Shanxiopitys zhangziensis gen. et sp. nov. Analyses of growth pattern and anatomical characteristics of the fossil woods indicate these trees grew under optimal growing conditions, and without seasonal growth cessation. However, climate signals from leaf fossils, vertebrate fossils and sedimentary evidences indicate a strongly seasonal climate in North China during the Lopingian. Thus, it is speculated that these trees likely lived in the gallery forests, which were distributed along the paleo-rivers within a seasonal landscape in the central North China block during the Lopingian.

Influence of Sub-Cloud Secondary Evaporation Effects on the Stable Isotopes in Precipitation of Urumqi Glacier No. 1, Eastern Tianshan
Mengyuan Song, Zhongqin Li, Feiteng Wang, Xin Zhang
2024, 35(1): 177-189. doi: 10.1007/s12583-021-1522-z

In arid regions, the stable hydrogen and oxygen isotopic composition in raindrops is often modified by sub-cloud secondary evaporation when they descend from cloud base to ground through the unsaturated air. As a result of kinetic fractionation, the slope and intercept of the δ2H-δ18O correlation equation decrease. The variation of deuterium excess from cloud base to the ground is often used to quantitatively evaluate the influence of secondary evaporation effect on isotopes in precipitation. Based on the event-based precipitation samples collected at Urumqi Glacier No. 1, eastern Tianshan during four-year observation, the existence and impact of secondary evaporation effects were analyzed by the methods of isotope-evaporation model. Under high air temperature, small raindrop diameter and precipitation amount, and low relative humidity conditions, the remaining rate of raindrops is small and the change of deuterium excess is large relatively, and the slope and intercept of δ2H-δ18O correlation equation are much lower than those of Global Meteoric Water Line, which mean that the influence secondary evaporation on precipitation enhanced. While on the conditions of low air temperature, high relative humidity, heavy rainfall, and large raindrop diameter, the change of deuterium excess is small relatively and the remaining rate of raindrops is large, and the slope and intercept of δ2H-δ18O correlation equation increase, the secondary evaporation is weakened. The isotope-evaporation model described a good linear correlation between changes of deuterium excess and evaporation proportion with the slope of 0.90‰/%, which indicated that an increase of 1% in evaporation may result in a decrease of deuterium excess about 0.90‰.

Characteristics and Genesis of Acid Drainage Contamination from a Rock Tunneling Project Site
Yanyun Li, Zejiao Luo, Shihua Qi
2024, 35(1): 190-200. doi: 10.1007/s12583-021-1551-7

While acid mine drainage (AMD) issues have become a topic of global concern, few studies have focused on acid drainage problems of non-mining activities. We conducted field research and a series of laboratory experiments to investigate the characteristics, release processes and formation of acid drainage contamination. Spoil rock samples and adjacent surface water, groundwater, soil and sediment samples were collected at a railway tunnel construction site in central China, and various parameters, such as the pH, mineral ion concentrations, and heavy metal concentrations, were measured. Based on the measured concentrations, surface water and sediments were seriously contaminated by acids, sulfate salts and heavy metals. Contamination in surface water showed a decreasing tendency as the distance from the spoils increased, while that in sediments showed a greater influence of coprecipitation and adsorption processes of heavy metal ions. The eluviation experiments of three rock samples indicated that R2 (silty fine sandstone) was the most likely major acid drainage contributor. Thiobacillus ferrooxidans was cultured and isolated from contaminated water to study the oxidation conditions during the release processes. The significant release of acid drainage when air and bacteria were both in the culture container suggested that oxygen and bacteria were necessary to produce acid drainage from spoils.

First Record of Cyclocarya from the Early Oligocene Qaidam Basin, North Tibet: Implications for the Paleogeography and Paleoecology
Yafei Hou, Bowen Song, Xiangchuan Li, Fang Han, Xu Zhang, Kexin Zhang
2024, 35(1): 201-211. doi: 10.1007/s12583-021-1580-2

As the largest intermontane basin in the northeastern Tibetan Plateau (TP), the Qaidam Basin provides unique insight into paleoclimatic change and its relationship with global change and uplift on the TP. In this study, based on morphological comparison, fossil fruit of Cyclocarya from the Early Oligocene Shangganchaigou Formation in the Qaidam Basin is assigned as Cyclocarya cf. weylandii. The discovery of Cyclocarya cf. weylandii demonstrates the occurrence of Cyclocarya in the Oligocene sediment in Qaidam Basin. This is the first record of Cyclocarya fossil of Early Oligocene Age in China and indicates that Cyclocarya has existed on the northeastern TP since at least the Early Oligocene. The living analogues of the current fossil now lives in sub-tropical China, where the East Asian Monsoon is prevalent. Integrating the new fossils and previously reported fossil remains of plants and fishes, it can be inferred that the Early Oligocene Qaidam Basin was primarily influenced by westerly circulation and had a relatively warm and humid climate, which was in sharp contrast to the present-day climate in Qaidam Basin.

Engineering Geology and Geo-hazards
Preliminary Results of the Seismicity Monitoring Experiment around the 2019 Mw5.4 Earthquake Epicenter in the Central South China Sea Basin
Wenfei Gong, Aiguo Ruan, Xiongwei Niu, Zhenjie Wang, Pingchuan Tan, Xiaodong Wei, Wei Wang, Zhengyi Tong, Liqun Cheng, Fansheng Kong, Shaoping Lu, Jianke Fan, Weiwei Ding, Jinyao Gao, Chunguo Yang, Jiabiao Li
2024, 35(1): 212-220. doi: 10.1007/s12583-021-1604-y

On September 5, 2019, a moderate earthquake of Mw5.4 unexpectedly occurred in the apparently quiescent central basin of the South China Sea. We immediately carried out a seismicity monitoring experiment around the epicenter by using broadband ocean bottom seismometers (OBS) for the following three scientific targets. The first is knowing the earthquake seismogenic mechanism, fault structure and further development. The second is finding the role of the residual spreading ridge playing in earthquake processes and further revealing the deep structures of the ridge directional turning area. The third is confirming the existence and significance of the so called "Zhongnan fault". This paper reports the preliminary results of the first phase experiment. Five OBSs were deployed for seismicity monitoring with a duration of 288 days, but only three were recovered. Micro-earthquakes were firstly detected by an automatic seismic phase picking algorithm and then were verified by analyzing their seismic phases and time-frequency characteristics in detail. A total of 21, 68 and 89 micro-earthquakes were picked out from the three OBSs respectively within the distance of 30 km. The dominant frequency of these micro-earthquakes is 12–15 Hz, indicating tectonic fracturing. During the first two months after the mainshock the seismicity was relatively stronger, and micro-earthquakes were still occurring occasionally till the end of observation, indicating the epicenter area is active. We used Match & Locate method to locate 57 micro-earthquakes preliminarily. Their spatial distribution shows that the seismicity is developed mainly along the NE direction roughly parallel to the residual ridge with depth variations between 10–20 km.

Dynamic Effect of Landslides Triggered by Earthquake: A Case Study in Moxi Town of Luding County, China
Hongfu Zhou, Fei Ye, Wenxi Fu, Bin Liu, Tian Fang, Rui Li
2024, 35(1): 221-234. doi: 10.1007/s12583-022-1806-y

The dynamic effect is a very important issue widely debated by scholars when studying the genetic and disaster-causing mechanisms of earthquake-triggered landslides. First, the dynamic effect mechanism and phenomena of earthquake-triggered landslides were summarized in this paper. Then, the primary types of dynamic effects were further used to interpret the Mogangling landslide in Moxi Town of Luding County, China. A field investigation, remote sensing, numerical calculation and theoretical analysis were carried out to illustrate the failure mechanism of slope rock masses affected by earthquakes. The interaction between seismic waves and slope rock masses and the induced dynamic effect of slope rock masses were primarily accounted for in the analysis. The slope topography, rock mass weathering and unloading characteristics, river erosion, regional seismogenic structure, and rock mass structure characteristics were also discussed. The results showed that the formation of the Mogangling landslide was mainly related to the high amplification effect of seismic acceleration and back slope effects, interface dynamic stress effects, and double-sided slope effects of seismic waves caused by the catastrophic Ms 7.75 Moxi Earthquake in 1786. The principles for the site and route selection of large-scale infrastructure in the planning stage and the scientific prevention of seismic geological disasters were proposed on the basis of the dynamic effect of earthquake-induced landslides.

Investigation on the Deformation and Failure Patterns of Loess Cut Slope Based on the Unsaturated Triaxial Test in Yan'an, China
Lina Ma, Shengwen Qi, Songfeng Guo, Qiangbing Huang, Xiaokun Hou
2024, 35(1): 235-247. doi: 10.1007/s12583-021-1554-4

The large-scale implementation of the Gully Stabilization and Land Reclamation (GSLR) project induces various failures of loess slopes due to excavation in Yan'an, China. However, the deformation and failure behavior of these excavated loess slopes have not been fully understood. In this study, field investigation was undertaken for analyzing the distributions and failure features of excavation-induced loess slope failures. It is found that plastic failure mainly occurs in Q3 loess layers and brittle failure in Q2. To understand the underlying failure mechanism, a series of triaxial shear tests were conducted on intact Q3 and Q2 loess samples that with different water contents, namely natural water content (natural), dry side of the natural value (drying 5%), and wet side (wetting 5%). The characteristics of stress-strain curves and failure modes of the samples were analyzed. Results show that the stress-strain curves of Q2 samples are dominated by strain-softening characteristics, while Q3 samples mainly exhibit strain-harden features except in the drying state. Correspondingly, shear failures of Q3 specimens are mainly caused by shear crack planes (single, X or V-shaped). For Q2 loess, the dominance of tensile cracks is observed on the surface of damaged specimens. These disclose the different failure modes of excavated slopes located in different strata, that is, the arc sliding failure of Q3 loess slopes and the stepped tensile failure of Q2 loess slopes, and are helpful in the design and management of the ongoing GSLR projects in the Loess Plateau.

Dynamic Stability and Fuzzy Reliability Analysis of Toppling Perilous Rock Under Seismic Excitation
Linfeng Wang, Jixu Zhang, Wanchun Xia, Xiaoming Huang, Guojin Tan
2024, 35(1): 248-262. doi: 10.1007/s12583-022-1740-z

To predict the occurrence of the collapse disaster in toppling perilous rock under the action of bidirectional earthquakes, the dynamic stability and fuzzy reliability calculation method of toppling perilous rock under the action of bidirectional earthquakes is proposed. First, the mass viscoelasticity model is used to simulate two main control surfaces of toppling perilous rock, the seismic dynamic response model and motion equation of toppling perilous rock are established based on the D'Alembert principle, and the Newmark-β method is used to solve the dynamic motion equation. Then, the instability event of toppling perilous rock is considered a fuzzy event, the membership function expression of the stability coefficient of toppling perilous rock is determined based on the fuzzy failure criterion, the calculation equations of the toppling perilous rock dynamic stability coefficient and fuzzy reliability are established, and the fuzzy reliability evaluation method based on the probability distribution of reliability is proposed. Finally, the influence of different superposition modes of seismic excitation on the fuzzy reliability of toppling perilous rock is analyzed. The calculation results of toppling perilous rock in the engineering case show that the fuzzy reliability calculated after considering the fuzzy failure criterion is reduced by 10.73% to 25.66% compared with the classical reliability. Considering the bidirectional seismic excitation, the fuzzy reliability of toppling perilous rock is reduced by 5.46% to 14.89%. Compared with using the acceleration peak time encounter mode to superpose the seismic excitation, the fuzzy reliability of toppling perilous rock is reduced by 3.4% when the maximum action effect time encounter mode is adopted.

Debris Flow Susceptibility Evaluation in Meizoseismal Region: A Case Study in Jiuzhaigou, China
Yongwei Li, Linrong Xu, Yonghui Shang, Shuyang Chen
2024, 35(1): 263-279. doi: 10.1007/s12583-022-1803-1

Jiuzhaigou is situated on a mountain-canyon region and is famous for frequent tectonic activities. An abundance of loose co-seismic landslides and collapses were produced on gullies after the Jiuzhaigou Earthquake on August 8, 2017, which was served as material source for debris flow in later years. Debris flow appears frequently which are seriously endangering the safety of people's lives and properties. Even the earliest debris flow appeared in areas where no case ever reported before. The debris flow susceptibility evaluation (DFSE) is used for predicting the areas prone to debris flow, which is urgently required to avoid hazards and help to guide the strategy of preventive measures. Therefore, this work employs debris flow in Jiuzhaigou to reveal the characteristics of disaster-pregnant environment and to explore the application of machine learning in DFSE. Some new viewpoints are suggested: (ⅰ) Material density factor of debris flow is first adopted in this work, and it is proved to be a critical factor for triggering debris flows by sensitivity analysis method. (ⅱ) Deep neural network and convolutional neural network (CNN) achieve relatively good area under the curve (AUC) values and are 0.021–0.024 higher than traditional machine learning methods. (ⅲ) Watershed units combined with CNN-based model can achieve more accurate, reliable and practical susceptibility map. This work provides an idea for prevention of debris flow in mountainous lands.

Quantitatively Evaluating the Erosion and Preservation of Supergene Oxide Zones: Evidence from the Yulong Porphyry Cu Deposit, Eastern Tibetan Plateau
Xiao-Dong Deng, Jian-Wei Li
2024, 35(1): 280-282. doi: 10.1007/s12583-023-1952-x
Building a More Sustainable Chinese Loess Plateau
Peiyue Li, Xiaomei Kou, Yong Wang, Le Niu
2024, 35(1): 283-287. doi: 10.1007/s12583-024-1970-3

The Chinese Loess Plateau, a region of remarkable ecological and economic value, grapples with significant water management challenges due to its distinctive geology and climate. This perspective offers a short review of the eco-environmental protection measures undertaken in the Loess Plateau, underscoring the transformative impacts of initiatives such as the "Grain for Green" project. However, it also highlights the enduring challenges, including land degradation, water resources issues, socio-economic inequities, and the implications of climate change. Particularly, water management emerges as a pivotal issue with far-reaching repercussions for soil conservation, biodiversity, and human livelihoods. The paper concludes by proposing future actions, emphasizing the necessity for policy modifications, novel initiatives, and research to tackle these challenges and foster sustainable development in the Loess Plateau. The insights gained from this region could offer invaluable lessons for other regions confronted with similar challenges, thereby contributing to global efforts to mitigate desertification and champion sustainable development.

Identification and Characteristics Analysis of Micro-Seismic Signals in the Haima Seep Area
Xiangchun Wang, Bing Nie, Zhiyu Wu, Weiwei Wang, Hua Chen
2024, 35(1): 288-291. doi: 10.1007/s12583-024-1968-x
Holocene Hydroclimatic Variations in the Asian Drylands: Current Understanding and Future Perspectives
Guoqiang Ding, Shengqian Chen, Yuanhao Sun, Shuai Ma, Jianhui Chen
2024, 35(1): 292-295. doi: 10.1007/s12583-023-1958-4
Integrating Shipborne Images with Multichannel Deep Learning for Landslide Detection
Pengfei Feng, Changdong Li, Shuang Zhang, Jie Meng, Jingjing Long
2024, 35(1): 296-300. doi: 10.1007/s12583-023-1957-5
An Advanced Image Processing Technique for Backscatter-Electron Data by Scanning Electron Microscopy for Microscale Rock Exploration
Zhaoliang Hou, Kunfeng Qiu, Tong Zhou, Yiwei Cai
2024, 35(1): 301-305. doi: 10.1007/s12583-024-1969-9

Backscatter electron analysis from scanning electron microscopes (BSE-SEM) produces high-resolution image data of both rock samples and thin-sections, showing detailed structural and geochemical (mineralogical) information. This allows an in-depth exploration of the rock microstructures and the coupled chemical characteristics in the BSE-SEM image to be made using image processing techniques. Although image processing is a powerful tool for revealing the more subtle data "hidden" in a picture, it is not a commonly employed method in geoscientific microstructural analysis. Here, we briefly introduce the general principles of image processing, and further discuss its application in studying rock microstructures using BSE-SEM image data.

A Three-Dimensional DEM Method for Trajectory Simulations of Rockfall under Irregular-Shaped Slope Surface and Rock Blocks
Liang Chen, Weiqian Zeng, Xianbiao Wang, Yang Ye, Yunfeng Ge, Dongming Gu, Shan Dong
2024, 35(1): 306-312. doi: 10.1007/s12583-023-1959-3
Groundwater Quality and Vulnerability Assessment in a Semiarid Karst Region of Northern China
Ran An, Shu Wang, Zongjun Gao, Zhenyan Wang, Wei Li, Qijun Deng, Lü Lin, Yuanqing Liu
2024, 35(1): 313-316. doi: 10.1007/s12583-021-1538-4