2022 Vol. 13, No. 3

Research Paper
Universal precursor seismicity pattern before locked-segment rupture and evolutionary rule for landmark earthquakes
Hongran Chen, Siqing Qin, Lei Xue, Baicun Yang, Ke Zhang
2022, 13(3): 101314. doi: 10.1016/j.gsf.2021.101314
Abstract(93) HTML PDF(49)
Abstract:
Despite extensive investigations, no precursor patterns for reliably predicting major earthquakes have thus far been identified. Seismogenic locked segments that can accumulate adequate strain energy to cause major earthquakes are highly heterogeneous and low brittle. The progressive cracking of the locked segments with these properties can produce an interesting seismic phenomenon: a landmark earthquake and a sequence of smaller subsequent earthquakes (pre-shocks) always arise prior to another landmark earthquake within a well-defined seismic zone and its current seismic period. Applying a mechanical model, magnitude constraint conditions, and case study data of 62 worldwide seismic zones, we show that two adjacent landmark earthquakes reliably occur at the volume-expansion point and peak-stress point (rupture) of a locked segment; thus, the former is an identified precursor for the latter. Such a precursor seismicity pattern before the locked-segment rupture has definite physical meanings, and it is universal regardless of the focal depth. Because the evolution of landmark earthquakes follows a deterministic rule described by the model, they are predictable. The results of this study lay a firm physical foundation for reliably predicting the occurrence of future landmark earthquakes in a seismic zone and can greatly improve our understanding of earthquake generation mechanism.
Unwrapping reworked crust at the Columbia supercontinent margin within central southern Amazon Craton using multi-source geophysics and geochronology data synergy
João G. Motta, P.G. Betts, V.T. Meira, V.G. Trevisan, C.R. de Souza Filho
2022, 13(3): 101348. doi: 10.1016/j.gsf.2022.101348
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The geometry and evolution of pre-existing basement in accretionary belts bordering supercontinents are often unclear. Integrative interpretation of long-wavelength potential field satellite data can image deep crust structure, improving our understanding of lithospheric processes that formed these margins bottom-up. Here, we present a multidisciplinary interpretation of the lithospheric architecture of the central southern Amazon Craton, a fragment of an accretionary belt at the southwestern Columbia supercontinent margin. Satellite-borne gravity and magnetic data, airborne magnetic data, passive seismic (Vp/Vs ratio, crustal thickness) and seismic tomography data reveals that basement terranes from the interior of the craton extend into the accretionary margin of Columbia. We demonstrate a vertically heterogeneous structure with an underlying strongly reworked pre-Columbia tectonic wedge that sustained prolonged modification during the supercontinent assembly as corroborated by Nd isotope and geochronology data. Nd isotope data suggest that the protracted orogenic wedge was influenced by subduction angle shifts over time, including addition of substantial juvenile material during slab retreat events. This interplay promoted Craton growth at the supercontinent margin while keeping a subtle record of the pre-existing framework. Our findings point to the possible misrepresentation of basement extension and geometry of supercontinent margins elsewhere.
Massive feature extraction for explaining and foretelling hydroclimatic time series forecastability at the global scale
Georgia Papacharalampous, Hristos Tyralis, Ilias G. Pechlivanidis, Salvatore Grimaldi, Elena Volpi
2022, 13(3): 101349. doi: 10.1016/j.gsf.2022.101349
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Statistical analyses and descriptive characterizations are sometimes assumed to be offering information on time series forecastability. Despite the scientific interest suggested by such assumptions, the relationships between descriptive time series features (e.g., temporal dependence, entropy, seasonality, trend and linearity features) and actual time series forecastability (quantified by issuing and assessing forecasts for the past) are scarcely studied and quantified in the literature. In this work, we aim to fill in this gap by investigating such relationships, and the way that they can be exploited for understanding hydroclimatic forecastability and its patterns. To this end, we follow a systematic framework bringing together a variety of –mostly new for hydrology– concepts and methods, including 57 descriptive features and nine seasonal time series forecasting methods (i.e., one simple, five exponential smoothing, two state space and one automated autoregressive fractionally integrated moving average methods). We apply this framework to three global datasets originating from the larger Global Historical Climatology Network (GHCN) and Global Streamflow Indices and Metadata (GSIM) archives. As these datasets comprise over 13,000 monthly temperature, precipitation and river flow time series from several continents and hydroclimatic regimes, they allow us to provide trustable characterizations and interpretations of 12-month ahead hydroclimatic forecastability at the global scale. We first find that the exponential smoothing and state space methods for time series forecasting are rather equally efficient in identifying an upper limit of this forecastability in terms of Nash-Sutcliffe efficiency, while the simple method is shown to be mostly useful in identifying its lower limit. We then demonstrate that the assessed forecastability is strongly related to several descriptive features, including seasonality, entropy, (partial) autocorrelation, stability, (non)linearity, spikiness and heterogeneity features, among others. We further (i) show that, if such descriptive information is available for a monthly hydroclimatic time series, we can even foretell the quality of its future forecasts with a considerable degree of confidence, and (ii) rank the features according to their efficiency in explaining and foretelling forecastability. We believe that the obtained rankings are of key importance for understanding forecastability. Spatial forecastability patterns are also revealed through our experiments, with East Asia (Europe) being characterized by larger (smaller) monthly temperature time series forecastability and the Indian subcontinent (Australia) being characterized by larger (smaller) monthly precipitation time series forecastability, compared to other continental-scale regions, and less notable differences characterizing monthly river flow from continent to continent. A comprehensive interpretation of such patters through massive feature extraction and feature-based time series clustering is shown to be possible. Indeed, continental-scale regions characterized by different degrees of forecastability are also attributed to different clusters or mixtures of clusters (because of their essential differences in terms of descriptive features).
Granular titanite from the Roter Kamm crater in Namibia: Product of regional metamorphism, not meteorite impact
Aaron J. Cavosie, Christopher J. Spencer, Noreen Evans, Kai Rankenburg, Robert J. Thomas, Paul H. Macey
2022, 13(3): 101350. doi: 10.1016/j.gsf.2022.101350
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Accessory minerals with so-called granular texture have risen in importance as geochronological tools for U-Pb dating of meteorite impact events. Grain-scale recrystallization, typically triggered by a combination of high-strain deformation and post-impact heating, can create a polycrystalline microstructure consisting of neoblasts that expel radiogenic Pb, which are thus ideal for isotopic dating. While granular domains in zircon and monazite from shocked rocks have been demonstrated to preserve impact ages, few U-Pb dating studies have been conducted on granular microstructures in titanite (CaTiSiO5). Here we report the occurrence of granular-textured titanite from ∼2020 Ma granite basement rock exposed in the rim of the 4–5 Ma Roter Kamm impact structure in Namibia. Orientation mapping reveals two microstructurally distinct titanite populations: one consisting of strained/deformed grains, and the other consisting of grains that comprise aggregates of strain-free neoblasts. In situ U-Pb geochronology on 37 grains shows that most grains from both titanite populations yield indistinguishable U-Pb dates of ca. 1025 Ma, consistent with the observed microstructures forming during the Mesoproterozoic Namaqua Orogeny. Only four grains preserved older age domains, recording ca. 1875 Ma Paleoproterozoic metamorphism. Two significant observations emerge: (1) none of the analyzed titanite grains yield the 2020 Ma igneous crystallization age previously established from zircon in the same sample, and (2) no age-resetting was detected that could be attributed to the 4 to 5 Ma Roter Kamm impact event. Despite the similarity of the neoblastic microstructure to minerals from other sites with an established impact provenance, the granular texture and near-complete Pb-loss in titanite from Roter Kamm granite instead records a Paleo- to Mesoproterozoic polymetamorphic history, rather than Miocene age shock-related processes. These results highlight the critical importance of grain-scale context for interpretation of U-Pb data in granular titanite, and the potential for misinterpreting inherited (pre-impact) microstructures as impact-related phenomenon in target rocks with a complex geological history.
Isla San Pedro Nolasco as a Late Miocene intrusive record at the eastern margin of the Gulf of California: Insights from geological, geochemical and geochronological studies
L.A. Velderrain-Rojas, J.R. Vidal-Solano, L.M. Alva-Valdivia, R. Vega-Granillo, M. López-Martinez
2022, 13(3): 101351. doi: 10.1016/j.gsf.2022.101351
Abstract:
Isla San Pedro Nolasco (ISPN) is a structural high bounded by inactive dextral oblique-slip faults in the east-central part of the Gulf of California rift zone and is composed of intrusive rocks not exposed on other Gulf of California islands. Here we present the reconnaissance results from geological mapping, as well as first geochemical and geochronological data for the ISPN intrusive complex. The intrusive rocks compose a sheet-like body of intermediate and felsic composition intruded by an intermediate and acidic dike swarm. All intrusive rocks (host and dikes) range in age from ca. 9 Ma to 10 Ma (40Ar/39Ar) and show a hydrous ferromagnesian mineral association (amphibole and biotite) with a calc-alkalic and transitional affinity. This hydrated mineralogical association has not been recognized in the coeval rocks along the onshore western margin of the North American plate (coastal Sonora). However, such hydrous mineralogical association is found in the coeval rift transitional volcanic rocks from the Baja California Microplate at Santa Rosalía and Bahía de Los Ángeles – Bahía de Las Ánimas. The ISPN continental block, at least 40 km long, has been pulled apart by transtensional faulting of the late Miocene Gulf of California shear zone before the westward migration of the North America-Pacific plate boundary at ca. 3–2 Ma. Eventually, ISPN became isolated as an island during the late Miocene flooding of the Gulf of California seaway.
Seismicity modulation by external stress perturbations in plate boundary vs. stable plate interior
Batakrushna Senapati, Bhaskar Kundu, Shuanggen Jin
2022, 13(3): 101352. doi: 10.1016/j.gsf.2022.101352
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Characterization of critically stressed seismogenic fault systems in diverse tectonic settings can be used to explore the stress/frictional condition of faults, along with its sensitivity for seismicity modulation by periodic stress perturbation. However, the process of seismicity modulation in response to external stress perturbation remains debated. In this paper, the characteristic difference in the seismicity modulation due to resonance destabilization phenomenon governed by rate-and-state friction is presented and validated with the globally reported cases of seismicity modulation in diverse tectonic settings. The relatively faster-moving plate boundary regions are equally susceptible for both shorter-period (e.g., semi-diurnal, diurnal, and other small tidal constituents) and long-period (e.g., semi-annual, annual, pole tide and pole wobble) seismicity modulation processes in response to stress perturbations from natural harmonic forcing, including tidal, semi-annual, annual, or multi-annual time scales. In contrast, slowly deforming stable plate interior regions and diffuse deformation zones appear to be more sensitive for long-period seismicity modulation of semi-annual, annual, or even multi-annual time scales but less sensitive for short-period seismicity modulation. This finding is also supported by the theoretical model predictions from the resonance destabilization process and worldwide documented natural observations of seismicity modulation in diverse types of tectonic settings.
Environmental fate and health exposures of the geogenic and anthropogenic contaminants in potable groundwater of Lower Ganga Basin, India
Indrani Mukherjee, Umesh Kumar Singh
2022, 13(3): 101365. doi: 10.1016/j.gsf.2022.101365
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The study evaluated the sources and controlling factors of the groundwater contaminants in an agroeconomic region of Lower Ganga Basin using principal component analysis (PCA), multivariable linear regressions (MLR), correlation analysis, and hierarchical cluster analysis, and evaluated the public health risks using the Latin Hypercube Sampling, goodness-of-fit statistics, Monte Carlo simulation and Sobol sensitivity analysis based on the 1000 samples collected in two sampling cycles (N = 1000). The study reveals that the dissolution of fluoride-bearing minerals and semi-arid climate regulate the fluoride concentrations (0.10–18.25 mg/L) in groundwater. Extensive application of inorganic nitrogenous fertilizers and livestock manure mainly contributed to elevated nitrate levels (up to 435.0 mg/L) in groundwater. The health risks analysis indicates that fluoride exposure is more prevalent in the residents of each age group than the nitrate and both contaminants exhibited higher non-carcinogenic health risks on the infant and child (minor) age groups compared to adolescents and adults. Based on the cokriging interpolation mapping, the minor residents of 17.88%–23.15% of the total area (4545.0 km2) are vulnerable to methemoglobinemia whereas the residents of all age-groups in 38.47%–44.45% of the total area are susceptible to mild to severe dental/skeletal fluorosis owing to consumption of untreated nitrate and fluoride enriched groundwater. The Sobol sensitivity indices revealed contaminant levels, groundwater intake rate and their collective effects are the most influential factors to pose potential health risks on the residents. Artificial recharge and rainwater harvesting practices should be adopted to improve the groundwater quality and the residents are advised to drink purified groundwater.
Rapid screening of Zr-containing particles from Chang’e-5 lunar soil samples for isotope geochronology: Technical roadmap for future study
Jin-Hua Li, Qiu-Li Li, Liang Zhao, Jin-Hai Zhang, Xu Tang, Li-Xin Gu, Qian Guo, Hong-Xia Ma, Qin Zhou, Yan Liu, Pei-Yu Liu, Hao Qiu, Gang Li, Lin Gu, Shun Guo, Chun-Lai Li, Xian-Hua Li, Fu-Yuan Wu, Yong-Xin Pan
2022, 13(3): 101367. doi: 10.1016/j.gsf.2022.101367
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New samples returned by China Chang’e-5 (CE-5) mission offer an opportunity for studying the lunar geologic longevity, space weathering, and regolith evolution. The age determination of the CE-5 samples was among the first scientific questions to be answered. However, the precious samples, most in the micrometer size range, challenge many traditional analyses on large single crystals of zircon developed for massive bulk samples. Here, we developed a non-destructive rapid screening of individual zirconium-containing particle for isotope geochronology based on a Micro X-ray fluorescence analysis (µXRF). The selected particles were verified via scanning electron microscopy (SEM), 3D X-ray microscopy (XRM), and focused ion beam scanning electron microscopy (FIB-SEM) techniques, which showed that zirconium-bearing minerals with several microns were precisely positioned and readily suitable for site-specific isotopic dating by second ion mass spectrometry (SIMS). Such protocol could be also applicable in non-destructively screening other types of particles for different scientific purposes. We therefore proposed a correlative workflow for comprehensively studying the CE-5 lunar samples from single particles on nanometer to atomic scales. Linking various microscopic and spectromicroscopic instruments together, this workflow consists of six steps: (1) single-particle selection with non-destructive µXRF technique, (2) 2D/3D morphological and structural characterization with a correlative submicron 3D XRM and nanoscale resolution FIB-SEM imaging methods, (3) SEM analysis of the surface morphology and chemistry of the selected particle, (4) a series of microscopic and microbeam analyses (e.g., SEM, electron probe microanalysis, and SIMS) on the cross-section of the selected particle to obtain structural, mineralogical, chemical, and isotopic features from the micron to nanometer scale, (5) advanced 2D/3D characterization and site-specific sample preparation of thin foil/tip specimens on a microregion of interest in the selected particle with FIB-SEM technique, and (6) comprehensive analyses on the FIB-milled specimens at nanometer to atomic scale with synchrotron-based scanning transmission X-ray microscopy, analytic transmission electron microscopy, and atom probe tomography. Following this technical roadmap, one can integrate multiple modalities into a uniform frame of multimodal and multiscale correlated datasets to acquire high-throughput information on the limited or precious terrestrial and extraterrestrial samples.
Crust-derived felsic magmatism in the Emeishan large igneous Province: New evidence from zircon U-Pb-Hf-O isotope from the Yangtze Block, China
Hao Zou, Cheng-Hui Hu, M. Santosh, Hai-Feng Chen, Chang-Cheng Huang, Xin-Wei Chen, Hong-Kui Li, Xin Jin, Li-Ming Yu, Min Li
2022, 13(3): 101369. doi: 10.1016/j.gsf.2022.101369
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Numerous intrusive bodies of mafic–ultramafic to felsic compositions are exposed in association with volcanic rocks in the Late Permian Emeishan large igneous province (ELIP), southwestern China. Most of the granitic rocks in the ELIP were derived by differentiation of basaltic magmas with a mantle connection, and crustal magmas have rarely been studied. Here we investigate a suite of mafic dykes and I-type granites that yield zircon U-Pb emplacement ages of 259.9 ± 1.2 Ma and 259.3 ± 1.3 Ma, respectively. The εHf(t) values of zircon from the DZ mafic dyke are –0.3 to 9.4, and their corresponding TDM1 values are in the range of 919–523 Ma. The εHf(t) values of zircon from the DSC I-type granite are between –1 and 3, with TDM1 values showing a range of 938–782 Ma. We also present zircon O isotope data on crust-derived felsic intrusions from the ELIP for the first time. The δ18O values of zircon from the DSC I-type granite ranges from 4.87‰ to 7.5‰. The field, petrologic, geochemical and isotopic data from our study lead to the following salient findings. (i) The geochronological study of mafic and felsic intrusive rocks in the ELIP shows that the ages of mafic and felsic magmatism are similar. (ii) The DZ mafic dyke and high-Ti basalts have the same source, i.e., the Emeishan mantle plume. The mafic dyke formed from magmas sourced at the transitional depth between from garnet-lherzolite and spinel-lherzolite, with low degree partial melting (<10%). (iii) The Hf-O isotope data suggest that the DSC I-type granite was formed by partial melting of Neoproterozoic juvenile crust and was contaminated by minor volumes of chemically weathered ancient crustal material. (iv) The heat source leading to the formation of the crust-derived felsic rocks in of the ELIP is considered to be mafic–ultramafic magmas generated by a mantle plume, which partially melted the overlying crust, generating the felsic magma.
Understanding the spatial representativeness of air quality monitoring network and its application to PM2.5 in the mainland China
Ling Su, Chanchan Gao, Xiaoli Ren, Fengying Zhang, Shanshan Cao, Shiqing Zhang, Tida Chen, Mengqing Liu, Bingchuan Ni, Min Liu
2022, 13(3): 101370. doi: 10.1016/j.gsf.2022.101370
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Air pollution has seriously endangered human health and the natural ecosystem during the last decades. Air quality monitoring stations (AQMS) have played a critical role in providing valuable data sets for recording regional air pollutants. The spatial representativeness of AQMS is a critical parameter when choosing the location of stations and assessing effects on the population to long-term exposure to air pollution. In this paper, we proposed a methodological framework for assessing the spatial representativeness of the regional air quality monitoring network and applied it to ground-based PM2.5 observation in the mainland of China. Weighted multidimensional Euclidean distance between each pixel and the stations was used to determine the representativeness of the existing monitoring network. In addition, the K-means clustering method was adopted to improve the spatial representativeness of the existing AQMS. The results showed that there were obvious differences among the representative area of 1820 stations in the mainland of China. The monitoring stations could well represent the PM2.5 spatial distribution of the entire region, and the effectively represented area (i.e. the area where the Euclidean distance between the pixels and the stations was lower than the average value) accounted for 67.32% of the total area and covered 93.12% of the population. Forty additional stations were identified in the Northwest, North China, and Northeast regions, which could improve the spatial representativeness by 14.31%.
Reconstruction of the mid-Devonian HP-HT metamorphic event in the Bohemian Massif (European Variscan belt)
Stephen Collett, Karel Schulmann, Piérig Deiller, Pavla Štípská, Vít Peřestý, Marc Ulrich, Yingde Jiang, Luc de Hoÿm de Marien, Jitka Míková
2022, 13(3): 101374. doi: 10.1016/j.gsf.2022.101374
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Mid-Devonian high-pressure (HP) and high-temperature (HT) metamorphism represents an enigmatic early phase in the evolution of the Variscan Orogeny. Within the Bohemian Massif this metamorphism is recorded mostly in allochthonous complexes with uncertain relationship to the major tectonic units. In this regard, the Mariánské Lázně Complex (MLC) is unique in its position at the base of its original upper plate (Teplá-Barrandian Zone). The MLC is composed of diverse, but predominantly mafic, magmatic-metamorphic rocks with late Ediacaran to mid-Devonian protolith ages. Mid-Devonian HP eclogite-facies metamorphism was swiftly followed by a HT granulite-facies overprint contemporaneous with the emplacement of magmatic rocks with apparent supra-subduction affinity. New Hf in zircon isotopic measurements combined with a review of whole-rock isotopic and geochemical data reveals that the magmatic protoliths of the MLC, as well as in the upper plate Teplá-Barrandian Zone, developed above a relatively unaltered Neoproterozoic lithospheric mantle. They remained coupled with this lithospheric mantle throughout a geological timeframe that encompasses separate Ediacaran and Cambrian age arc magmatism, protracted early Paleozoic rifting, and the earliest phases of the Variscan Orogeny. These results are presented in the context of reconstructing the original architecture of the Variscan terranes up to and including the mid-Devonian HP-HT event.
In situ Lu–Hf phosphate geochronology: Progress towards a new tool for space exploration
Stijn Glorie, Thomas Burke, Martin Hand, Alexander Simpson, Sarah Gilbert, Benjamin Wade
2022, 13(3): 101375. doi: 10.1016/j.gsf.2022.101375
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Geochronology is fundamental to understanding planetary evolution. However, as space exploration continues to expand, traditional dating methods, involving complex laboratory processes, are generally not realistic for unmanned space applications. Campaign-style planetary exploration missions require dating methods that can (1) rapidly resolve age information on small samples, (2) be applied to minerals common in mafic rocks, and (3) be based on technologies that could be installed on future rover systems. We demonstrate the application of rapid in situ microanalytical Lu–Hf phosphate geochronology using samples of pallasite meteorites, which are representative examples of the deep interiors of differentiated planetoids that are generally difficult to date. Individual pallasites were dated by laser ablation tandem mass-spectrometry (LA-ICP-MS/MS), demonstrating a rapid novel method for exploring planetary evolution. Derived formation ages for individual pallasites agree with traditional methods and have <2% uncertainty, opening an avenue of opportunity for remote micro-analytical space exploration.
Polystyrene nanoplastics aggravated ecotoxicological effects of polychlorinated biphenyls in on zebrafish (Danio rerio) embryos
Yizheng Li, Shulin Liu, Qiuping Wang, Yanling Zhang, Xikun Chen, Lei Yan, Muhammad Junaid, Jun Wang
2022, 13(3): 101376. doi: 10.1016/j.gsf.2022.101376
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In view of the accumulation of nanoplastics (NPs) in the food chain of environment and animals, and the good adsorption properties of nano-plastics to toxic substances, it is necessary to explore the influence of NPs in living organisms. In this study, single and joint toxicological effects of polystyrene nanoplastics (PS-NPs, size 80 nm) and polychlorinated biphenyls (PCBs), were explored in freshwater aquatic animal model zebrafish (Danio rerio). Our study found that exposure to single PS-NPs induced mild acute toxicity, albeit the combined exposure of PS-NPs and polychlorinated biphenyls aggravated the toxicity of PCBs in a dose-dependent manner. Results from gene expression profiling showed that NPs exposure could activate detoxification process, resulting in a slight up-regulation of antioxidant genes (sod1, gstp1), bone development genes (bmp2, bmp4) and cardiac gene (tbx20); while PCBs suppressed the detoxification through down-regulation of these genes, and the addition of NPs will exacerbate the impact of PCBs on gene suppression. Importantly, the results of in vivo purification experiments found that NPs showed prolonged retention in liver, intestine and gills of zebrafish and they might have crossed biological barrier and accumulate in lipid-rich tissues and excretion does not appear as the significant pathway for their elimination. In conclusion, the toxic effects of polychlorinated biphenyls on chorionic protected embryos were not significant as zebrafish chorion plays an important role in resisting the invasion of pollutants; PCBs can seriously damage the bone and heart development of zebrafish, while the presence of NPs significantly enhanced the toxicity of PCBs in zebrafish, which is an alarming concern for growing NPs levels and ecological safety in aquatic environment.
Syn-rift to post-rift tectonic transition and drainage reorganization in continental rifting basins: Detrital zircon analysis from the Songliao Basin, NE China
Ying Song, Jianye Ren, Keyu Liu, Dawei Lyu, Xinjie Feng, Yuan Liu, Andrei Stepashko
2022, 13(3): 101377. doi: 10.1016/j.gsf.2022.101377
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Tectonic transition from a syn-rift stage to subsequent post-rift stage is an important mechanism in the evolution of extensional basins. The sedimentary infill records the crustal response to this process. We have obtained new detrital zircon U-Pb and Lu-Hf signatures from the Lower Cretaceous stratigraphic successions encompassing the commonly accepted syn- to post-rift transition boundary, the T4 unconformity, in the Songliao Basin, NE China. These constrain the Songliao Basin’s evolution from its center to distal margins, providing insights into the sediment provenance and dispersal pattern over the tectonic transition. Analysis of zircons from the syn-rift (the Shahezi and Yingcheng formations) and immediate post-rift (the Lower and Middle Denglouku Formation) stages reveals Phanerozoic age populations with positive Ɛ values, which were derived from the proximal juvenile mantle-derived melt origin bedrocks of the Songliao Block. In contrast, the overlying samples from the Upper Denglouku Formation deposited in the subsequent post-rift stage contain exotic and ancient zircon populations with ages of 2.5 Ga & 1.8 Ga and complex hafnium signatures, characteristic of a mixed origin. These are interpreted to be transported from distant cratonic terranes via larger drainage networks. It is obvious that the sediment dispersal pattern switched from being a local and hydrologically closed “intraregional” pattern to a “transcontinental” pattern during the transition. The time lag between the development of the T4 unconformity and the drainage reorganization also ensures a distinguishable ∼3 Myr (106103 Ma, Late Albian) transition period of regional extent. During this transition stage, syn-rift faulting was replaced by post-rift thermal subsidence, exhibiting a uniform sag configuration. Our new findings are important for understanding other continental rift basins during syn- to post-rift transition, which often demonstrates a complex interaction between the linkage and integration of sub-basins, and the reorganization of fluvial drainages and catchment systems.
Centrifugal model test on a riverine landslide in the Three Gorges Reservoir induced by rainfall and water level fluctuation
Fasheng Miao, Yiping Wu, Ákos Török, Linwei Li, Yang Xue
2022, 13(3): 101378. doi: 10.1016/j.gsf.2022.101378
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Frequent soil landslide events are recorded in the Three Gorges Reservoir area, China, making it necessary to investigate the failure mode of such riverside landslides. Geotechnical centrifugal test is considered to be the most realistic laboratory model, which can reconstruct the required geo-stress. In this study, the Liangshuijing landslide in the Three Gorgers Reservoir area is selected for a scaled centrifugal model experiment, and a water pump system is employed to retain the rainfall condition. Using the techniques of digital photography and pore water pressure transducers, water level fluctuation is controlled, and multi-physical data are thus obtained, including the pore water pressure, earth pressure, surface displacement and deep displacement. The analysis results indicate that: Three stages were set in the test (waterflooding stage, rainfall stage and drainage stage). Seven transverse cracks with wide of 1–5 mm appeared during the model test, of which 3 cracks at the toe landslide were caused by reservoir water fluctuation, and the cracks at the middle and rear part were caused by rainfall. During rainfall process, the maximum displacement of landslide model reaches 3 cm. And the maximum deformation of the model exceeds 12 cm at the drainage stage. The failure process of the slope model can be divided into four stages: microcracks appearance and propagation stage, thrust-type failure stage, retrogressive failure stage, and holistic failure stage. When the thrust-type zone caused by rainfall was connected or even overlapped with the retrogressive failure zone caused by the drainage, the landslide would start, which displayed a typical composite failure pattern. The failure mode and deformation mechanism under the coupling actions of water level fluctuation and rainfall are revealed in the model test, which could appropriately guide for the analysis and evaluation of riverside landslides.
Focus Paper
Probabilistic assessment of slope failure considering anisotropic spatial variability of soil properties
Longlong Chen, Wengang Zhang, Fuyong Chen, Dongming Gu, Lin Wang, Zhenyu Wang
2022, 13(3): 101371. doi: 10.1016/j.gsf.2022.101371
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Anisotropic spatial variability of soil properties is frequently encountered in geotechnical engineering practice due to the complex depositional process. To quantitatively evaluate the response of slope failure related to anisotropic spatial variability of soil properties and reveal the underlying influence of anisotropic spatial variability of soil properties on the slope reliability, this study integrates the random finite difference method (RFDM) into a probabilistic assessment framework and adopts general spatial variability and a cohesive-frictional soil slope example for illustration. A parametric analysis is carried out to investigate the influence of general anisotropic spatial variability of soil properties on slope failure probability and failure characteristics. The results show that the directional angles of scales of fluctuation of general anisotropic spatial variability significantly affect the slope failure probability. The dominant failure mode is the intermediate type in most cases of general anisotropic spatial variability, which is distinguished from the shallow failure mode occurring in the homogenous state. Overestimation of cross-correlation between c and φ (), scales of fluctuation ( and ) in general anisotropic spatially variable soils significantly influences the average slip mass volumes of deep and multi-slip failure mode. Compared with transverse anisotropic spatial variability, general anisotropic spatial variability significantly amplifies the effects of , and on slope reliability.