Study of Melting Temperature of Metals: Pressure Dependence

The melting temperature of metals are studied using the statistical moment method, going the quasi-harmonic appromations. The melting temperature of metals are calculated as a function of the pressure. We discuss the pressure dependence of melting temperatures of Ce, Fe metals and compare the present results with those of the experimental results

Study on active tectonic faults using soil radon gas method in Viet Nam

This paper presents the results of soil radon gas measurement in three areas, including Thac Ba and Song Tranh 2 hydropower plants, and the planned locations of the nuclear power plants Ninh Thuan 12 using solid-state nuclear track detectors (SSNTD) with the aim of clarifying the activity of tectonic faults in these areas. The activity of tectonic faults was assessed through radon activity index KRn (the ratio between anomaly and threshold), which was divided into 5 levels as follows ultra-high (KRn 10), high (10≥KRn 5), high (5≥KRn 3), medium (3≥KRn 2) and low (KRn≤2). Soil radon gas measurement results showed that in the radon gas concentrations in the Thac Ba hydropower plant area ranged from 72 Bq/m3 to 273.133 Bq/m3 and maximum radon activity index KRn reached 9.75 (high level). High KRn indexes show Chay River fault active in recent time and the sub-meridian distribution of Rn anomalies suggested a right-slip motion of the fault. Rn concentrations in the Ninh Thuan 12 areas ranged from 6 Bq/m3 to 52.627 Bq/m3, however, the KRn indexes were mostly low (KRn≤3) and the highest value was only 3.42, suggesting that expression of activity of the tectonic faults in this region is not clear, even no expression of fault activity. In the Song Tranh 2 hydropower plant and adjacent areas, radon concentrations ranged from 29 Bq/m3 to 77.729 Bq/m3 and maximum KRn index was 20.16 (ultra-high level). The faults having clearer activity expression are Hung Nhuong - Ta Vy, Song Tra Bong and some high order faults, especially the northwest - southeast segments of these faults or their intersections with the northwest - southeast faults. In addition, the high values KRn in the mentioned intersections can be evidenced for the activeness of northwest - southeast faults at the present time. The studies on active faults using soil radon gas method were performed in areas with very different geological and structural features, but the results are well consistent with the results of previous investigations obtained by other methods. It confirmed the effectiveness and capability of soil radon gas geochemistry applying to study active tectonic faults.ReferencesAl-Hilal M., Al-Ali A., 2010. The role of soil gas radon survey in exploring unknown subsurface faults at Afamia B dam, Syria. Radiat. Meas, 45, 219-224.Amponsah,   P.,   Banoeng-Yakubo,   B.,   Andam,   A., Asiedu, D.,  2008. Soil  radon  concentration along fault systems in parts of south eastern Ghana. J. Afr. Earth Sci. 51, 39-48.Asumadu-Sakyi A.B., Fletcher J.J., Oppon O.C., Qua- shie F.K., Wordson D.A., Adjei C.A., Amartey E.O., Darko E.O. and Amponsah P.,  2011. Preliminary Studies on Geological Fault Location Using Solid State Nuclear Track Detection. 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North-directed Triassic nappes in Northeastern Vietnam (East Bac Bo)

International audienceA careful re-examination of the previous tectonic descriptions and the acquisition of new structural and kinematic data have been undertaken in northeastern Vietnam. The structure of the area consists of a system of slightly metamorphosed but ductilely deformed nappes, including recumbent folds, formed during the Triassic, prior to the unconformable deposition of the Upper Triassic terrigenous sediments. These results confirm the previous interpretation of " preyunnanaises nappes ", represented by Middle-Upper Paleozoic foliated limestone resting through a flat mylonitic contact over an intermediate " Song Mien unit " (Deprat, 1915), the latter made essentially of deformed Lower Triassic sedimentary and volcanic formations, which previously filled the Song Hien rift (Bourret, 1922). In the external part of the belt, the Triassic strata conformably overlie slightly deformed and unmetamorphosed Upper Paleozoic rocks, forming an autochthonous domain. Alternatively, the same Triassic succession can be seen resting tectonically through décollement zones, directly over the Middle Paleozoic marbles, to form a distinct but subsidiary allochthonous unit. Our data show that the Song Chay orthogneiss and its Lower Paleozoic sedimentary country rocks belong to the main nappe. They also demonstrate that this nappe was transported to the N-NE. A newly discovered ophiolitic mélange of supposed oceanic nature and Triassic age, lying along the Song Chay Fault, North of the Nui Con Voi, could hypothetically represent the rooted zone of the nappe. A Tertiary overprinting event, in particular accommodated by strike-slip movements, likely accounts for the present orocline of NE Vietnam

Geochronology and isotope analysis of the Late Paleozoic to Mesozoic granitoids from Northeastern Vietnam and implications for the evolution of the South China block

International audienceIn northeastern Vietnam, Late Paleozoic and Permo-Triassic granitic plutons are widespread, but their tectonic significance is controversial. In order to understand the regional magmatism and crustal evolution processes of the South China block (SCB), this study reports integrated in situ U-Pb, Hf-O and Sr-Nd isotope analyses of granitic rocks from five plutons in northeastern Vietnam. Zircon SIMS U-Pb ages of six granitic samples cluster around in two groups 255 Ma - 228 Ma and 90 Ma. Bulk-rock εNd(t) ranges from -11 to -9.7, suggesting that continental crust materials were involved in their granitic genesis. In situ zircon Hf-O isotopic measurements for the granitic samples yield a mixing trend between the mantle- and supracrustal-derived melts. It is suggested that the granitic rocks were formed by re-melting of the continental crust. These new data are compared with the Paleozoic and Mesozoic granitic rocks of South China. We argue that northeastern Vietnam belongs to the South China block. Though still speculated, an ophiolitic suture between NE Vietnam and South China, so-called Babu ophiolite, appears unlikely. The Late Paleozoic to Mesozoic magmatism in the research area provides new insights for the magmatic evolution of the South China block

LA-ICPMS zircons U/Pb dating of Permo-Triassic and Cretaceous magmatisms in Northern Vietnam - Geodynamical implications

International audienceIn northeastern Vietnam, the major tectonic episode responsible for nappes emplacement is Triassic. These allochtonous structures are intruded by granitic melts. Two post-tectonic massifs showing no sign of deformation have been dated by the LA-ICPMS zircon U-Pb techniques. Dating reveals a multiphase history with zircon cores showing evidence of Proterozoic magmatism. The emplacement of the Phia Bioc granite intrusive in allochtonous units is 248-245 Ma, an age which assesses a younger limit for the major nappes tectonic. This tectonic could be synchronous of the tectonometamorphic strike-slip faulting events (250-245 Ma) defined in the Truong Son Belt as the Indosinian orogen. The Phia Bioc intrusion is probably linked with the intra-plate magmatism of the Emeishan Large Igneous Province or with magma- tism associated with the Paleotethys closure. The age of the Phia Oac granite intrusion in displaced units is much younger, at 87.3 ± 1.2 Ma. This granite is probably linked to the magmatic activity produced dur- ing the Paleo-Pacific plate subduction under the SE Asia continental plate during the Mesozoic. Although the Cenozoic Red River fault system is close to these two plutons, this last thermotectonic episode has not been strong enough to disturb the U/Pb system. Zircons rims do not show any Tertiary magmatic or meta- morphic overprint

The South China Block-Indochina collision: where, when, and how?

International audienceThis study uses new field observations and existing studies to shed new light on the origin and significance of two NW-SE striking orogens in NW and NE Vietnam. We conclude that the architecture of each belt is a stack of NE-directed nappes formed either under deep ductile synmetamorphic conditions, or under shallow depth in the SW and NE parts, respectively. The Song Ma zone and Song Chay ophiolitic melange represent two ophiolitic sutures. However, the Late Permian Song Da and Babu mafic rocks are not ophiolites but intraplate basalts related to the Emeishan plume. A Late Triassic unconformity, the 225-205 Ma postorogenic plutonism, and the 250-230 Ma syntectonic metamorphism support an Early to Middle Triassic age for these tectonic events. Both NW and NE belts are due to SW-directed subduction with arc magmatism, ocean closure, and continental collision. Though two contemporary S-dipping subduction zones might explain the structural evolution of the two belts, a single convergent system, offset by the Tertiary Red River fault, is preferred as this S-directed subduction better accounts for the Late Permian intraplate magmatism. This scenario is discussed in the general geodynamic framework of SE Asia

Predicting land use effects on flood susceptibility using machine learning and remote sensing in coastal Vietnam

Flood damage is becoming increasingly severe in the context of climate change and changes in land use. Assessing the effects of these changes on floods is important, to help decision-makers and local authorities understand the causes of worsening floods and propose appropriate measures. The objective of this study was to evaluate the effects of climate and land use change on flood susceptibility in Thua Thien Hue province, Vietnam, using machine learning techniques (support vector machine (SVM) and random forest (RF)) and remote sensing. The machine learning models used a flood inventory including 1,864 flood locations and 11 conditional factors in 2017 and 2021, as the input data. The predictive capacity of the proposed models was assessed using the area under the curve (AUC), the root mean square error (RMSE), and the mean absolute error (MAE). Both proposed models were successful, with AUC values exceeding 0.95 in predicting the effects of climate and land use change on flood susceptibility. The RF model, with AUC = 0.98, outperformed the SVM model (AUC = 0.97). The areas most susceptible to flooding increased between 2017 and 2021 due to increased built-up area. HIGHLIGHTS Machine learning algorithms were applied for flood susceptibility modeling.; The RF model had the highest AUC value (0.98).; The areas highly flood susceptibility increased between 2017 and 2021.