Acta Geologica Sinica ‐ English Edition最新文献

The water conductivity of karst collapsed column is affected by multiple factors such as the characteristics of its own column filling, structure and mining disturbance. As a structural water-conducting channel, fault usually plays a controlling role in hydrogeological structure. During the process of mine water hazard prevention and control, it was discovered that the lithology composition, compaction and cementation degree and water physical properties of karst collapsed column fillings were all non-conducting water, but due to the influence of combined development faults, some exploration drill holes showed concentrated water outflow. Based on this, the scientific hypothesis was proposed that fault cutting leads to water conduction in karst collapsed columns. The study comprehensively used methods like chronology, exploration data analysis, and hydrochemical testing to analyze the chronological relationship between faults and karst collapsed columns, their spatial relationship, outlet point distribution and water chemical properties, and the impact of faults on the water-conductivity of karst collapsed columns, which proved the effect of fault cutting on changing water conductivity of karst collapsed column. The research showed that later fault cutting through karst collapsed columns turned the originally non-conductive karst collapsed columns into water-conductive collapsed columns at the fault plane, creating a longitudinally connected water-conducting channel. A new model of fault cutting karst collapsed column to change the original water conductivity of karst collapsed column was proposed. The research results can provide a theoretical basis for the prediction of the water conductivity of the karst collapsed column. According to whether the karst collapsed column was cut by the fault, it was predicted theoretically, so as to determine the key areas of water conductivity detection and prevention and control, and has broad application prospects under the background of source control of mine water disaster.

The Upper Cretaceous successions of Wadi Umm-Khayshar, southern Galala Plateau, North Eastern Desert, Egypt, are composed of highly diversified faunas and subdivided from base to top into the Galala (Middle–Late Cenomanian), Maghra El Hadida (Latest Cenomanian–Late Turonian), Matulla (Coniacian–Santonian), and Sudr (Campanian–Maastrichtian) formations. Five ammonite biozones are recorded in the studied section: Neolobites vibrayeanus, Vascoceras cauvini (late Cenomanian), Vascoceras proprium, Choffaticeras segne, and Coilopoceras requienianum (Turonian) zones. The paleoenvironments of the Upper Cretaceous succession are interpreted based on detailed study and microfacies analysis that reflect a deposition in a homoclinal ramp platform ranging from intertidal to deep subtidal. The paleoecology of the Cenomanian–Turonian succession in the studied section is explained based on a detailed study of macrofaunal associations and sedimentary facies. Quantitative analysis (Q-mode cluster analysis, using the Raup–Crick Paired group method) of 1029 macrobenthic specimens, including 45 species of mollusks and echinoids yielded five macrofaunal associations (A–E) that are described and interpreted as remnants of communities. The nektonic elements are represented by 235 cephalopod specimens of 20 species; heatmap cluster analyses show the distribution of these specimens during the Upper Cenomanian–Turonian stages. Environmental parameters (substrate consistency, rate of sedimentation, water energy, surface-water productivity, and oxygen availability) controlled the distribution of the studied macrofauna. The five associations are divided into two major groups: low-stress associations (A, B, C, and D), and a high-stress association (E). The low stress associations are recorded from two different habitats: (1) a high-energy, firm substrate habitat, dominated by epifaunal bivalves, large epifaunal gastropods and a regular echinoid; (2) a low-energy, soft substrate habitat dominated by infaunal bivalves and echinoids. The high stress association is dominated by only two species and recorded from a high-energy shoal environment during a regression phase. A detailed study of macrobenthos and cephalopods provides a good paleoecological understanding of Cenomanian–Turonian succession in the Wadi Umm–Khayshar section.

Controlled by fluctuating paleoclimates and sedimentary environments, the organic and inorganic features of the Lucaogou Formation exhibit strong heterogeneity in the vertical profile, challenging conventional geological interpretation. To elucidate the possible influence of heterogeneity on resource evaluation, a high-resolution sampling approach was applied to an 86.2 cm long core from the Lucaogou Formation of the Jimsar sag in the Junggar Basin. 86 sets of samples were micro-drilled from the core and subjected to comparative Rock-Eval pyrolysis. Following the classical guidelines, the organic abundance, kerogen type, and maturity of source rocks were exhaustively analyzed. Experimental results revealed that organic richness and composition vary significantly under different sedimentary backgrounds, which in turn leads to differential hydrocarbon generation. The combination of hydrocarbon generation, transport, and expulsion results in peculiar patterns for hydrocarbon accumulation in the Lucaogou Formation. Laminated shales in the Lucaogou Formation serve as both hydrocarbon source rocks and reservoirs, with laminae being migration pathways. Organic-rich dolomites in the Lucaogou Formation have a considerable hydrocarbon-generating capacity and present the characteristics of self-generation and self-storage. However, massive mudstones act purely as hydrocarbon source rocks.

Large basins are currently the global focus for geothermal development, with their hydrothermal system being controlled by a variety of factors, such as basement relief and fracture development. Donglihu is located at the north of the Cangxian uplift in the North China Basin, the concentrated geothermal resource development zone in North China. This study systematically collects temperature logging data and long-term dynamic monitoring of water level and water quality as well as group well tracer test data carried out in this area in recent years, on the basis of which the hydrothermal controlling role of the deep hidden faults is systematically analyzed. The results show that the Cangdong fault communicates with different geothermal reservoirs in the shallow part and plays a specific role in the water-heat channel of the local area. As a result, the high-value area of the geothermal temperature gradient in the sedimentary layer of the Donglihu area is distributed around the Cangdong fault. The geothermal reservoir temperature of the Minghuazhen Formation within the influence of the fault is also significantly higher than the regional average, the hydraulic head of different geothermal reservoirs showing a consistent and synergistic trend. However, the water quality has been stable for many years without any apparent changes. This understanding has a particular significance for further deepening understanding of the geothermal genesis mechanism in sedimentary basins and guiding future geothermal exploration and development in the Donglihu area.

The 7 ka old Qixiangzhan lava flow (QXZ, Tianchi volcano) represents the last eruptive event before the 946 CE, caldera-forming ‘Millennium’ eruption (ME). Petrographic, whole rock, mineral composition, Sr-Nd isotopic data on QXZ show that: (a) the lava consists of two components, constituted by comenditic obsidian fragments immersed in a continuous, aphanitic component; (b) both components have the same geochemical and isotopic variations of the ME magma. The QXZ and ME comendites result from fractional crystallization and crustal assimilation processes. The temperature of the QXZ magma was about 790°C and the depth of the magma reservoir around 7 km, the same values as estimated for ME. QXZ had a viscosity of 10^5.5–10⁹ Pa s and a velocity of 3–10 km/yr. The emplacement time was 0.5–1.6 yr and the flow rate 0.48–1.50 m³/s. These values lie within the range estimated for other rhyolitic flows worldwide. The QXZ lava originated through a mixed explosive–effusive activity with the obsidian resulting from the ascent of undercooling, degassing and the fragmentation of magma along the conduit walls, whereas the aphanitic component testifies to the less undercooled and segregated flow at the center of the conduit. The QXZ lava demonstrates the extensive history of the ME magma chamber.

As one of the most serious geological disasters in deep underground engineering, rockburst has caused a large number of casualties. However, because of the complex relationship between the inducing factors and rockburst intensity, the problem of rockburst intensity prediction has not been well solved until now. In this study, we collect 292 sets of rockburst data including eight parameters, such as the maximum tangential stress of the surrounding rock σ_θ, the uniaxial compressive strength of the rock σ_c, the uniaxial tensile strength of the rock σ_t, and the strain energy storage index W_et, etc. from more than 20 underground projects as training sets and establish two new rockburst prediction models based on the kernel extreme learning machine (KELM) combined with the genetic algorithm (KELM-GA) and cross-entropy method (KELM-CEM). To further verify the effect of the two models, ten sets of rockburst data from Shuangjiangkou Hydropower Station are selected for analysis and the results show that new models are more accurate compared with five traditional empirical criteria, especially the model based on KELM-CEM which has the accuracy rate of 90%. Meanwhile, the results of 10 consecutive runs of the model based on KELM-CEM are almost the same, meaning that the model has good stability and reliability for engineering applications.

We report new SHRIMP zircon U-Pb ages, zircon Lu-Hf isotopic and whole rock geochemical data from Permian granitoids located in the Alxa area of Inner Mongolia, China. In combination with published geochronological and geochemical data, the granitoids in the region can be divided into two age groups: ca. 285 Ma and ca. 269 Ma. The granitoids of the first group are mainly composed of calc-alkaline to high-K calc-alkaline, weakly peraluminous I-type granodiorites with ɛ_Hf(t) values of -19.6 to -4.3, which demonstrates evidence of crustal reworking; the granitoids of the second group, however, mainly consist of A-type granites that are high-K calc-alkaline to shoshonite, metaluminous to weakly peraluminous, and have high 10,000 × Ga/Al ratios (2.59–3.12) and ɛ_Hf(t) values ranging from –11.3 to –2.7, all of which demonstrates a mixed crust-mantle source. We interpret the granitoids of the first group to have formed during the subduction of Central Asian oceanic crust and the second group to have formed by the asthenospheric upwelling caused by the formation of slab windows during late ocean ridge subduction.

The petrogenesis and genetic link to polymetallic mineralization of the granites in the Dayishan complex, southern Hunan province remain debated. Here, we present an integrated study on the petrology, zircon U-Pb ages and whole-rock geochemistry for this complex. Our findings indicate that the southern complex consists of (amphibole-bearing) biotite granites and muscovite granites emplaced at 153–151 Ma, and the central and northern complex consists of two-mica granites and tourmaline-bearing muscovite granites, respectively with the former emplaced at 164 Ma and the latter at 150 Ma. The (amphibole-bearing) biotite granites have SiO₂ contents of 68.0–73.8 wt% and are enriched in alkalis and rare earth elements and depleted in Sr and Ba. They display Zr + Y + Ce + Nb > 350 ppm and 10000 × Ga/Al > 2.6 along with high zircon saturation temperatures (821–883°C). The two-mica granites and (tourmaline-bearing) muscovite granites have high SiO₂ (74.4–77.3 wt%) and low Ga/Al, Zr + Nb + Ce + Y, K/Rb, Zr/Hf, and Nb/Ta along with low zircon saturation temperatures (709–817°C). Geochemical characteristics suggest that the (amphibole-bearing) biotite granites are A-type granites generated through shallow dehydration melting of early Paleozoic granitoids, and that the two-mica granites and (tourmaline-bearing) muscovite granites are fractionated A-type granites produced through fractionation crystallization from the (amphibole-bearing) biotite granites accompanied by fluid fractionation.

Deciphering high-pressure granulite-facies metamorphism and anatexis within a collisional orogeny can provide crucial constraints on geodynamic evolution and melt activity during subduction and exhumation. Combining petrographic observations, mineral chemistry, REE in Grt-Cpx thermobarometry, and previous work, at least four stages are suggested for the metamorphic evolution of the mafic granulites in the South Altun, including the protolith stage, the high-pressure granulite-facies stage (909–1037°C and 17.3–30 kbar), medium-pressure granulite-facies overprint (9.1–11.9 kbar and 753–816°C), and subsequent late amphibolite-greenschist-facies metamorphism. Zircon U-Pb dating shows that the mafic granulites underwent high-pressure granulite-facies metamorphism at 497.2 ± 3.7 Ma, while the leucosome formed at 498.2 ± 2.9 Ma. Thus, the leucosomes from the host mafic granulite may have been formed at the high-pressure granulite-facies metamorphic event. The characteristics of zircon morphology, mineral inclusions, low Th/U values, HREE enrichment, and negative Eu anomalies indicate that these zircons from the leucosome were formed from the metamorphic melts. The characteristics of whole-rock major and trace elements as well as Hf isotopic features of zircons between the leucosomes and the host mafic granulite indicate that the melt may have been generated by the partial melting of the host mafic granulite.

The temporal and spatial evolution of the Ailao Shan–Red River (ASRR) fault zone, which serves as an important accommodation zone for the extrusion and escape of the Southeastern Tibetan Plateau, is crucial for analyzing the uplift and growth of the plateau. Based on the petrology and apatite fission track analysis, the tectonic history and active pattern of the ASRR fault zone since the middle Miocene are determined in this study. The ASRR fault zone exhibits 12–8 Ma and 8–4 Ma rapid cooling phases since the middle Miocene. The 12–8 Ma and 8–4 Ma cooling may imply that the dextral movement of the ASRR fault zone presents a migration trend from northwest to southeast, accompanied by the weakening of the activity intensity, which is directly related to deformation processes, including extrusion boundary migration and active tectonic movements of the southeastern Tibetan Plateau, since the middle–late Miocene.