Cretaceous Granitic Magmatism in South-Central Vietnam: Constraints from Zircon U–Pb Geochronology

South-central Vietnam abundantly presents magmatic rocks with larger volumes ofCretaceous granitic rocks. In this study, zircon U–Pb geochronology of granite samples from the Deoca,Ankroet, and Dinhquan complexes in south-central Vietnam are utilized to investigate Cretaceousgranitic magmatism. According to U–Pb analysis results, zircon ages of granitic rocks display the Deocaat ~113–92 Ma, the Ankroet at ~103–98 Ma, and the Dinhquan at ~97–113 Ma. The range of ages isnarrow from 113 to 92 Ma, with most common ages date at ~100 Ma. Published data and our resultsdisplay that Cretaceous granitic magmatism was active between ~87–118 Ma and most active at ~100Ma in south-central Vietnam. Additionally, the Deoca and Dinhquan complexes show inherited ages inTriassic followed by Proterozoic and Carboniferous to Ordovician. The obtained ages indicate that Itypegranitic rocks could be derived from melting of basement rocks. Our study suggests that I-typegranitic rocks in south-central Vietnam were significantly intruded around 100 Ma.

Green chitosan: thiourea dioxide cleaning gel for manganese stains on granite and glass substrates

The cleaning or removal of manganese stains on Cultural Heritage has not been much tested or successful so far. The aim of this article was to assess a new green cleaning gel for Mn-rich black-blue stains on different substrates. The black-blue stains were characterized at optical and chemical level through colour-related data, optical microscope, FTIR, XRF and XPS. Mn-stained granite found on historical churches at Vila Real (North of Portugal) and glass jars of Leclanché cells, belonging to the ISEP’s Museum (Portugal) collection, were the ideal case studies to test the efficiency of chitosan: thiourea dioxide (TD) cleaning gel. TD proved to be the best candidate to reduce insoluble manganese oxides, over Hydroxylamine Hydrochloride and Hydroxymethanesulfinic Acid. Cleaning assays performed on stained granite samples collected at a historical quarry and in situ application on stained granite churches allowed removal of the stains to a satisfactory level. Similar results were obtained on stained glass jars.

Mechanical Responses of a Deeply Buried Granite Exposed to Multilevel Uniaxial and Triaxial Cyclic Stresses: Insights into Deformation Behavior, Energy Dissipation, and Hysteresis

This article presents the results for cyclic uni/triaxial tests on the deeply seated granite samples drilled from a −915 m deep tunnel in Sanshandao (SSD) gold mine. The monotonic and cyclic tests were carried out to observe the mechanical responses of the granite samples under different loading regimes. The disparities concerning the strain evolution and compressive strength of granite samples considering monotonic and cyclic uniaxial and triaxial loading are presented. Deformation behaviour, dissipated energy, and hysteresis are documented and evaluated. Quantitative correlations between strain evolution and cyclic stress levels are revealed. The amount of energy transformation during uniaxial and triaxial cyclic loading is determined. The impacts of confining pressure level on ultimate strain, energy dissipation, and stress-strain phase shift are presented. The mechanical responses of the granite samples subjected to different stress paths and loading strategies are summarised, and corresponding interpretations are given to clarify the differences of mechanical behaviour encountered in distinct loading methods.

SPATIAL NONUNIFORM DISTRIBUTION OF 235U ISOTOPE AT SUPERCRITICAL FLUID EXTRACTION WITH CARBON DIOXIDE IN A GRADIENT TEMPERATURE FIELD

The spatial redistribution of the 235U isotope of natural uranium in a gradient temperature field along the height of the reactor in supercritical carbon dioxide has been experimentally investigated. The scheme of the reactor is given and the principle of operation of the reactor is described. The method of preparation of initial samples from granite samples containing natural uranium and the procedure of extraction are described. The conclusion about the spatial redistribution of 235U isotopes in supercritical carbon dioxide is based on the analysis of gamma spectra of extracts. It is shown that the concentration of the 235U isotope in a supercritical fluid is maximal near the lower heated flange of the reactor, and decreases with approaching the upper, cooled flange. It was concluded that the separation factor of the 235U isotope in supercritical carbon dioxide can be about 1.2 ± 0.12.

Study on the Mechanical Behavior and Acoustic Emission Properties of Granite under Triaxial Compression

To study the rock mechanical behaviors and damage process mechanism of granite samples under triaxial stress, conventional triaxial compression tests were carried out on an RMT-150B rock mechanics testing machine and acoustic emission detector. The test results show that the strength of the granite sample has a good linear relationship with the confining pressure, the cohesion force c of the granite samples is 29.37 MPa, and the internal friction angle is 54.23° by calculation based on the Mohr-Coulomb strength criterion. The larger the initial confining pressure of the rock sample is, the larger the crack initiation stress ( σ ci ) and dilatancy stress ( σ cd ) of the granite specimen are, the larger the energy values at the crack initiation point and dilatancy point are, and the larger the peak energy storage and energy release rate at the failure are. In the case of a small initial confining pressure, the AE ringdowning counts and the cumulative AE ringing counts increase to their maximum instantaneously at the peak stress point, and the damage of the sample develops rapidly. While the initial confining pressure is high, the AE ringing counts and the cumulative AE ringing counts of the granite specimens increase evenly, and the deformation damage of the granite specimens is slow. Before the crack initiation point, AE signals are mainly low-energy and low-frequency friction-type AE events, while after the dilatation point, AE signals of samples are mainly high-frequency and high-energy fracture-type AE events. The failure mode of granite samples judged by acoustic emission parameters according to the distribution of characteristic values of AE parameters RA and AF is consistent with the reality. The AE b value of the granite sample is large when the confining pressure is low, and there will be a sudden drop, the decrease time is late, and the decrease rate is large. Under the same stress level, the larger the confining pressure is, the larger the damage variable D is.

Green Chitosan:Thiourea Dioxide Cleaning Gel for Manganese Stains on Granite and Glass Substrates

The cleaning or removal of manganese stains on Cultural Heritage has not been much tested or successful so far. The aim of this article was to assess a new green cleaning gel for Mn-rich black-blue stains on different substrates. The black-blue stains were characterized at optical and chemical level through RGB data, colorimetry, optical microscope, FTIR, XRF and XPS. Mn-stained granite found on historical churches at Vila Real (North of Portugal) and glass jars of Leclanché cells, belonging to the ISEP’s Museum (Portugal) collection, were the ideal case studies to test the efficiency of Chitosan:Thiourea Dioxide (TD) cleaning gel. TD proved to be the best candidate to reduce insoluble manganese oxides, over Hydroxylamine Hydrochloride and Hydroxymethanesulfinic Acid. Cleaning assays performed on stained granite samples collected at a historical quarry and in situ application on stained granite churches showed the complete removal of the stains. Similar results were obtained on stained glass jars. This article presents an innovative, feasible and green Chitosan gel embedded with TD and phosphoric acid, applied to the cleaning of Mn-stained granite and glass substrates.