Solid Earth Sciences最新文献

This work presents the results of a study of radionuclide activity in cryoconite from glacier and glacial soil of the Central Caucasus. Cryoconite were sampled from the surface of the Garabashi glacier, and soil samples were taken from the humus horizon of periglacial mountain forest-meadow soil. Measurements were performed with low-background germanium gamma spectrometers located inside a passive shield consisting of ∼20 cm of copper, ∼15 cm of lead, and ∼8 cm of borated polyethylene. The specific activity of radionuclides (Be-7, K-40, Th-232, U-235, U-238, Cs-137) was established. It was revealed that all measured spectra contain γ-lines from decays of K-40, decay chains of U-238, U-235 and Th-232. In addition, the spectra of cryoconite samples from the Garabashi glacier show a 477.6 keV line from the decay of the cosmogenic isotope Be-7, and in the soil sample a 661.7 keV line from the radionuclide Cs-137. No radionuclide Be-7 was detected in the mountain forest-meadow soil. Radionuclide Cs-137 is present in the soil sample, while in cryoconite, is not detected. Radioisotope activities in the Garabashi glacier cryoconite, except for the cosmogenic isotope Be-7, do not differ significantly in terms of mass, i.e., the content of K-40, U-238, U-235 and Th-232 in them is approximately the same. The activity of all the studied radionuclides in the soil sample compared to cryoconite samples is lower, although the differences are not significant, except for Th-232, whose activity in soil is almost two times lower.

Buckling instability has been identified as a possible mechanism of pile failure in liquefiable ground and this failure mechanism is not explicitly mentioned in most of the design codes. Pile buckling would be affected, however, by various factors including liquefaction zone of foundations soils, axial loads of piles, geometry as well as arrangement of pile foundation, etc. An efficient approach using deterministic by Bhattacharya is proposed to compute the buckling instability in pile. This method is verified and validated using 3D finite-element simulation through OpenSeesPL. A more comprehensive study of numerical simulation would include the effects of various factors on the responses of piles and foundations soils due to seismic loading. The findings reported that an increase in axial loading would generally increase the excess pore pressure in soils and would generally increase the deflection and bending moment in piles and acceleration responses in soils. An increase in pile spacing would generally increase the deflection and bending moment in piles, as a result of more soil volume among the piles. An increase in diameter of pile would increase in rigidity and maximum bending capacity of piles and thus would resist more energy released in liquefiable ground that amplifies the deflection (curvature) of pile. A comparison of two approaches confirms the pile would be safe from buckling failure against soil liquefaction during seismic loading. Finally, this study would provide for predicting pile buckling instability and the behaviors of piles and foundation soils due to seismic shaking and liquefied ground.

The Xing–Meng Orogenic Belt hosts an amount of low-sulfidation epithermal gold deposits. However, the tectonic-magmatic setting remains problematic, which hinders understanding the factors that control the gold endowment in the region. Wulaga deposit is the largest low-sulfidation epithermal gold deposit in the northeastern Xing–Meng Orogenic Belt. Gold mineralization occurs in the crypto-explosive breccia zone of subvolcanic granodiorite porphyry. Zircon U–Pb ages of three granodiorite apophyses and previous pyrite Rb–Sr dating (113.8 ± 4.4 Ma) indicate granodiorite porphyry and gold mineralization was coeval. The ore-related granodiorite porphyry is moderate SiO₂, high-K calc-alkaline, and metaluminous, suggesting an I-type granite. Moreover, Wulaga granodiorite porphyry displays low initial ⁸⁷Sr/⁸⁶Sr ratios and positive ε_Nd(t) values with T_DM2(Nd) of 799.7–897.4 Ma and ε_Hf(t) values with T_DM2(Hf) of 652–785 Ma, indicating that it was derived from partial melting of the Neoproterozoic juvenile mafic lower crust. Ti-in-zircon thermometry, medium–high Sr/Y ratio, high Ba/La, and f_O2 value indicate that Wulaga granodiorite porphyry formed at relatively low temperatures (∼700 °C), rich water, and high fugacity within the stability field of garnet in the juvenile lower crust. Combined with ore-related tectonic-magmatic activities in the Wulaga, Dong'an, and Sandaowanzi gold deposits, the Early Cretaceous low-sulfidation epithermal gold deposits in the Xing–Meng Orogenic Belt were formed from magmatic-hydrothermal events triggered by mutual interaction between post-orogenic lithospheric extension related to the closure of the Mongol-Okhotsk Ocean and arc-back extension associated with rollback of the Paleo-Pacific Ocean plate. These data indicate the potential existence of the Early Cretaceous epithermal gold deposits that are related to the contemporaneous igneous activity.

The investigation of glacial sediments has not received a lot of attention, but the processes in place on the surface of glaciers are quite interesting and multidirectional. In this article, we focused on glacial sediments material sampled from the surface of the Bellingshausen Ice Dome (King George Island, South Shetland Islands, Antarctica). These sediments have different genesis: material from cryoconite holes, denuded layers of volcanic ash, flushed ash and soils and soil-like bodies formed in the glacial zone. Chemical analysis of the samples showed that the bulk composition of sediments is as follows: SiO₂ > Fe₂O₃ > Al₂O₃ > SO₃ > CaO > MgO > Na₂O > TiO₂ > K₂O > P₂O₅ > MnO (with SiO₂ content 50–55%, Fe₂O₃ – 17–23%, Al₂O₃ – 6–12%). The loss on ignition was maximum (10–11%) for samples taken at the top of the dome. Calculation of geochemical indexes showed that the mineral part of the samples is a product of erosion and sedimentation processes and is less chemically weathered in the lower part of the ice dome. The weathering type is fersiallitic. The maximum content of organogenic compounds (Total organic carbon – up to 5%, ammonium nitrogen – up to 116 mg/kg and mobile potassium – up to 373 mg/kg) also recorded at the top of the glacial dome; this may be associated with microbiological activity in cryoconite holes and the penetration of organic material from bird fauna. The low content of organogenic compounds on the slopes is caused by the processes of their washout with melt water. The content of trace metals Zn, Ni, and Pb found at higher elevations and distribution of Cu and Cd have more a local character associated with tourism activities and anthropogenic influence from year-round scientific stations. Thus, a number of multidirectional processes take place in the glacial sediments on the Bellingshausen Ice Dome, these are not simple denuded layers of ancient volcanic ash. The glacier cover can be considered as a “living” biogeochemical shell, accumulating products of microbiological and anthropogenic activity, products of erosion and sedimentation and organic matter of ornithogenic origin.

A new procedure has been developed for high precision and high accuracy Mg isotope analysis on multiple-collector inductively coupled plasma mass spectrometry using a critical mixture double spike technique. Errors arising from improper preparation of the critical double spike solutions are able to be corrected against the regression on a set of over- and under-spiked standards. Accuracy is ensured by correcting mass bias offset based on Monte Carlo calculations. Doping experiments indicate that the double spike method is robust to non-spectrum matrix effects. A long-term precision and accuracy of ±0.03‰ (2SD) was demonstrated for δ²⁶Mg by replicate analyses of well-characterized in-house pure Mg solutions and synthetic samples passed through the column chemistry, provided that each sample was measured four times. The robustness of the method was further assessed by replicate analyses of fifteen geological reference materials ranging from peridotite, basalt, granodiorite, carbonatite to seawater. Rock standards yielded consistently higher δ²⁶Mg by 0.076 ± 0.052‰ (2SD, N = 12) compared to data previously reported by standard-sample-bracketing from the same lab. This discrepancy might result from the difficulty in matching the matrices of natural samples exactly the same to the bracketing standards, even after purification, suggesting a careful evaluation on residual matrix effect for the standard-sampling-bracketing method. Our new data for geological reference materials serve as a reference for quality assessment and inter-laboratory comparison in future studies.

The shales of the Mamfe basin were geochemically analyzed to determine their paleosalinity and hydrothermal characteristics which existed at the time of their deposition. Elemental ratios such as boron/gallium (B/Ga), strontium/barium (Sr/Ba), and total sulphur/total organic carbon (S/TOC) and TOC/S were applied for paleosalinity reconstruction. The shales of the Mamfe basin show B/Ga is <3, Sr/Ba <0.2, and S/TOC is <0.1 and TOC/S >6 the values of the elemental ratio show that the Mamfe shales were deposited in a freshwater environment. For hydrothermal activities ratio, Sc/Cr was used and Binary diagrams TOC vs P and Co/Zn vs TOC were constructed to discriminate between normal water, mixed and hydrothermal influence. The Sc/Cr ratio was greater than 0.14 indicating that the shales in the Mamfe basin were deposited in a normal water environment with no influence from hydrothermal processes. The binary discriminant diagram of TOC vs P and Co/Zn vs TOC shows that all the shales were not influenced by any hydrothermal processes during the time of their deposition.