Geological Journal最新文献

The Feidong Complex, located on the northeastern margin of the Yangtze Craton, exposes Precambrian basement rocks and is the subject of debate regarding its tectonic affinity. In this study, we conducted in situ U–Pb dating and Hf isotope analyses of zircons from basement rocks within the Feidong Complex. The results reveal crystallisation ages of ca. 2.45, 2.0 and 0.8 Ga for the granitic gneiss, amphibole biotite plagiogneiss and mylonitised monzonitic granite, respectively. The basement rocks with ages of ca. 2.45 and 2.0 Ga exhibit negative zircon ε_Hf(t) values (−10.48 to −0.13) and older two-stage model ages (T_DM2 = 2974 to 3296 Ma). We compared the zircon U–Pb ages and Hf isotopic characteristics of the basement rocks from the Feidong Complex with those of the southern margin of the North China Craton and the northern margin of the Yangtze Craton. Additionally, we also compared the metamorphic grades of rocks between the Feidong Complex and Susong Complex of the Dabie orogenic belt. We found that the Feidong Complex and the northern margin of Yangtze Craton share comparable zircon U–Pb ages and Hf isotopic characteristics. However, the metamorphic grades of the Feidong Complex were distinct from those of the Susong Complex. In particular, the basement rocks with an age of ca. 2.45 Ga formed within a subduction setting; those with an age of ca. 2.0 Ga formed during the subduction and collision associated with the assembly of the Columbia supercontinent; and those with an age of ca. 0.8 Ga experienced extensional processes before the breakup of the Rodinia supercontinent.

Tunnel waste constitutes a prevalent by-product of highway construction in high-altitude mountainous and hilly regions. Sulphide minerals exhibit a unique distribution pattern within the alpine hills. Consequently, tunnel excavation can disrupt the stability of these sulphide minerals, rendering the tunnel waste susceptible to generating secondary environmental hazards during stockpiling. This research delves into the migration and transformation dynamics of potential environmental pollutants in tunnel waste through geoenvironmental simulation techniques. Controlled variables were employed to simulate various conditions, including surface illumination, internal anaerobiosis, water content and aerobic environments. The study's findings indicate that the presence of pyrite in the waste stream primarily drives the secondary contamination of the tunnel waste. Pyrite within the slag tends to react and form sulphuric acid in the stockpile environment, thus creating an acidic milieu that exacerbates the release of existing contaminants. The emergence of an anaerobic environment and a photocatalytic system composed of Fe/Ti substances in the waste stream serves to further accelerate pollutant release. This study thoroughly investigates the primary causes of environmental pollution during the stockpiling of tunnel slag and assesses the potential environmental impact scenarios. The outcomes of this research offer substantial theoretical and empirical support for the management of slag generated during the tunnel construction process.

Based on pressure test data, well logging data and geological conditions, the distribution and cause of overpressure in the western Qaidam Basin are analysed. The contribution of different overpressure causes is quantified, and the main controlling factors of overpressure at different evolution stages are further divided. This is useful for analysing the pressure state in different geological historical periods and indicating the direction of oil and gas migration. The research results show that the formation pressure coefficient in the western part of the Qaidam Basin is mainly in the range of 0.5–2.1, and the pressure coefficient generally decreases from the depression to the edge. According to the stress variation characteristics and logging response of overpressure, two models of acoustic travel time-vertical effective stress and electrical resistivity-vertical effective stress are established to identify and quantify the cause of overpressure for loading and unloading. Through the analysis of logging curves, acoustic velocity-density cross-plot and geological conditions, the causes of overpressure in western Qaidam Basin was clarified. The overpressure calculation results of different origins show that the main controlling factors of overpressure in the Kunbei fault stage are disequilibrium compaction and tectonic extrusion, with contribution rates of 38% and 52%, respectively. The overpressure in Mangya depression is caused by disequilibrium compaction, tectonic extrusion and hydrocarbon generation, with overpressure ratios of 30%, 32% and 38% respectively. The overpressure of the Dafengshan uplift can contribute up to 53% of the disequilibrium compaction, and the contributions of tectonic extrusion and hydrocarbon generation are 28% and 19%, respectively. Finally, the evolution of residual pressure in the upper segment of the Xiaganchaigou Formation ($��{E_3}^2�$) in western Qaidam Basin can be divided into four evolution stages: undercompaction stage (42.8–40.5 MPa), normal compaction stage (40.5–12.0 MPa), hydrocarbon generation pressurization stage (12.0–2.8 Ma) and pressure release stage (2.8 Ma-present).

A flare-up of granitoids occurred at 465–445 Ma in the South Altyn Tagh, synchronously with the exhumation of subducted continental crust. Nevertheless, it remains enigmatic whether a petrogenetic connection exists between them. Here, we report a 454–451 Ma monzogranite pluton, which is characterized by abundant inherited zircons, located in the northern margin of the South Altyn Tagh high-pressure (HP)—ultrahigh-pressure (UHP) metamorphic terrane. U–Pb ages and Hf–O isotopic compositions of inherited and synmagmatic zircons are investigated to trace the source rocks and petrogenesis of this pluton. The inherited zircons (zircons that predate the magmatism) exhibit a wide range of ages from 2618 to 484 Ma, displaying three major peaks at 1800–1100 Ma, 1000–800 Ma and 500 Ma. By comparing these inheritance age patterns with zircon spectra of main (meta-)sedimentary sequences and the widespread Early Neoproterozoic granites (presently as granitic gneisses) in South Altyn Tagh, along with zircon εHf(t) and whole-rock Nd isotopic composition, we argue that the main source rocks of the studied monzogranite are Early Neoproterozoic granitic gneisses and Late Mesoproterozoic paragneisses from the South Altyn Tagh HP–UHP metamorphic terrane. The ca. 500 Ma inherited zircons have a metamorphic origin, which is simultaneous with the peak metamorphic ages of HP–UHP metamorphic rocks in the Altyn Tagh Complex. These observations indicate that the source rocks of the monzogranite pluton are the subducted continental crust, which underwent metamorphism at ca. 500 Ma and followed by partial melting at 454–451 Ma. In addition, synmagmatic zircons exhibit variable δ¹⁸O and εHf(t) values ranging from 5.4 to 11.7‰ and from −19 to +10.3, respectively, indicating a minor contribution of mantle-derived melts in the formation of the monzogranite. Given the studied pluton and contemporaneous extensive granitoids (465–445 Ma), characterized by similar geochemistry and source rocks, are synchronous with the final exhumation of subducted South Altyn Tagh continental crust, we propose that the reworking of exhumed continental crust at middle to lower crustal depths is their main petrogenesis.

Iron speciation has emerged as a robust proxy for discerning oceanic redox conditions; nonetheless, it is subject to certain limitations. Specifically, the applicability of the degree of pyritization is contingent upon the presence of unequivocal evidence of an anoxic water column and its discriminatory capacity is limited to distinguish between ferruginous (anoxic) and euxinic conditions. This study highlights that through the integration of redox-sensitive trace metal enrichment data with Fe-speciation data, the depositional redox conditions for marine sediments can be established with greater certainty. Recently, a set of dedicated geological reference materials (BHW and WHIT) have been developed for validating the Fe-speciation analytical results for redox reconstruction studies; however, to the best of our knowledge, these reference materials are not characterized for trace and rare earth elements (REEs). In this connection, the BHW (oxic) and WHIT (anoxic) reference materials are measured for major, trace and REEs. After careful statistical considerations for these reference standards, a complete set of trace and REEs is reported. Furthermore, considering BHW and WHIT as oxic and anoxic end-members, respectively, the utility of trace metal enrichment and Fe-speciation data in combination has been discussed. The trace and REE concentrations of BHW and WHIT reported in this study will enhance their applicability as a reference material to understand ocean chemistry and the oxidation state of the ancient oceans.

Spodumene-bearing pegmatite dyke swarms have recently been discovered in the Chaqiabeishan area, at the northeastern margin of the Qinghai-Tibet Plateau in northwest China. In order to elucidate the connection between the Chaqiabeishan lithium pegmatites and Triassic magmatism and mineralization within the West Kunlun – Songpan -Garzê rare-metal belt, this study presents new columbite-group mineral and monazite U–Pb dating results, mineral chemistry, monazite in situ Nd isotope analyses and gamma-ray spectrometric measurements. Magmatism and mineralization at Chaqiabeishan mainly occurred ca. 216 Ma, and the mineralized pegmatites (Mn-rich columbite-group minerals, highly evolved monazite compositions and high effective uranium contents in the gamma-ray survey) were generated from the high degree of the fractional crystallization in a volatile-rich granitic magma. The source material of the Chaqiabeishan lithium pegmatites (ε_Nd(t) values from −14.4 to −12.8) was more enriched than that of other pegmatite-type lithium deposits (Jiajika and Bailongshan) in the West Kunlun – Songpan – Garzê rare-metal belt and is ascribed to melting of ancient crustal materials in the basement. These late-Triassic mineralizing events were closely related to the collision-related tectonic setting at the northeastern margin of the Tibetan-Qinghai Plateau, a product of Paleo-Tethys Ocean closure.

Tunnels stand as indispensable pillars of transportation infrastructure, assuming a central and transformative role in fostering the sustainable evolution of urban. The excavation process of tunnels presents a spectrum of geological challenges, encompassing the potential for instability and collapse. Ensuring the stability of the tunnel is a top priority in tunnel construction. The destabilization leading to collapse in certain tunnels is intricately connected to the structural planes of the rock mass. Accurately obtaining the distribution of structural planes within the rock mass is the necessary basis for maintaining the stability of the tunnel. The conventional Monte Carlo method generates each parameter of stochastic structural planes separately without considering the correlations between the parameters. To address this limitation, we propose a stochastic structural plane generation method based on deep generative model (DGM). The model takes the measured factual structural plane data as input, and the neural network realizes the generation of structural plane data with automatic learning of the distribution law of structural planes and the correlations between each parameters without assuming the probability distribution of stochastic structural planes in advance. This method has been used for stochastic structural plane generation of the rock mass in the Yuelongmen tunnel located in Mianyang City, Sichuan Province. The validation results show that the proposed DGM-based method automatically captures the correlation between structural plane parameters while ensuring the greater accuracy of the generated structural planes.

Skirted foundations are critical components in offshore applications where combined loads are common in deep-water environments. Their ultimate capacity under VH (vertical-horizontal) combined loading is traditionally determined using VH failure envelopes, which are primarily constructed using numerical methods. These methodologies, however, frequently ignore the spatial variability inherent in seabed soils due to geological formations. This paper investigates the effect of spatial variability of undrained shear strength and embedment ratio impact on the capacity of skirted foundations subjected to VH combined loading. For this, OptumG2 software is used to perform Monte Carlo simulation combined with random finite element limit analysis. This paper investigates the stochastic analysis of bearing capacity and failure envelopes, with a particular emphasis on understanding the effect of spatial correlation on undrained shear strength. The study focuses on the horizontal scale of fluctuation and the soil strength heterogeneity index, shedding insight on previously undiscovered areas. Novel findings highlight how a rigid base affects VH failure envelopes and offer insights into evaluating the vertical bearing capacity of skirted foundations. [Correction added on 8 July 2024, after first online publication: The above statement has been updated in this version.]

The Neotethyan Sanandaj–Sirjan Zone of western Iran has recorded major magmatic activities due to its continental arc tectonic setting during the Mesozoic. The Varcheh mafic intrusions were less-studied plutons in the northern Sanandaj–Sirjan Zone (SSZ). Field evidence, petrography, geochemistry and U–Pb geochronological data were used to determine petrographic composition, geochemical nature, crystallization age and also to suggest a conceptual tectonomagmatic model for their emplacement. Small plutonic bodies are dominantly composed of monzogabbro that have intruded into the Cretaceous sedimentary rocks. Based on U–Pb zircon datings, these rocks have crystallized at 125–118 Ma in late Early Cretaceous (Barremian–Aptian), and are older than the supposed ages reported on geological maps. Varcheh rocks are not just typical calc-alkaline rocks and some show alkaline affinity. Negative anomalies in Nb–Ta–Ti and enrichments in some large-ion lithophile elements on spider diagrams are consistent with a subduction-zone setting. Potential deep source for magma generation is partial melting of subcontinental lithospheric mantle wedge above a subducting slab of oceanic lithosphere. The spaces for the Varcheh mafic intrusions are accommodated by dominant dextral strike-slip movement in a continental arc experiencing extension during late Early Cretaceous subduction. According to the zircon U–Pb geochronology results in this paper and previous U–Pb ages in the northern part of the SSZ, the mid-Cretaceous magmatism reveals a significant NW-ward younging trend and migration of the magmatic arc from the Barremian–Aptian in south-east to the Albian–Cenomanian in the north-west.