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Thanh L.N.,Free University of Brussels | Thanh L.N.,Vietnam Institute of Geosciences and Mineral Resources | de Smedt F.,Free University of Brussels
Environmental Earth Sciences | Year: 2012

A Luoi is a Vietnamese-Laotian border district situated in the western part of Thua Thien Hue province, central Vietnam, where landslides occur frequently and seriously affect local living conditions. This study focuses on the spatial analysis of landslide susceptibility in this 263-km 2 area. To analyze landslide manifestation in the study area, causative factor maps are derived of slope angle, weathering, land use, geomorphology, fault density, geology, drainage distance, elevation, and precipitation. The analytical hierarchical process approach is used to combine these maps for landslide susceptibility mapping. A landslide susceptibility zonation map with four landslide susceptibility classes, i. e. low, moderate, high, and very high susceptibility for landsliding, is derived based on the correspondence with an inventory of observed landslides. The final map indicates that about 37% of the area is very highly susceptible for landsliding and about 22% is highly susceptible, which means that more than half of the area should be considered prone to landsliding. © 2011 Springer-Verlag. Source

Hieu P.T.,Hefei University of Technology | Hieu P.T.,CAS Institute of Geology and Geophysics | Chen F.-K.,Hefei University of Technology | Thuy N.T.B.,Vietnam Institute of Geosciences and Mineral Resources | And 2 more authors.
Journal of Geodynamics | Year: 2013

The late Permian granitoids exposed in the Phan Si Pan zone of northwestern Vietnam consist mainly of the Ye Yen Sun metaluminous granites and the Nam Xe-Tam Duong peralkaline granites. Laser ablation inductively coupled plasma mass spectrometry U-Pb zircon analysis reveals that both the granite suites were emplaced from 253Ma to 251Ma. They have a distinctive A-type geochemistry of high 10,000×Ga/Al ratios of 3.0-5.7 and are also characterized by elevated contents of high field strength elements, A/CNK values of 0.85-1.58, negative Eu-anomalies. Magmatic zircons from the granitoids exhibit positive initial eHf values ranging from 6.4 to 15.9 and yield single-stage depleted mantle Hf model ages of 257-663Ma. This Hf isotopic feature implies significant contribution of juvenile mantle material to the magmas of the spatially and temporally associated Ye Yen Sun metaluminous and Nam Xe-Tam Duong peralkaline granites. © 2012 Elsevier Ltd. Source

Tien Bui D.,Telemark University College | Ho T.-C.,Vietnam Institute of Geosciences and Mineral Resources | Pradhan B.,University Putra Malaysia | Pradhan B.,Sejong University | And 3 more authors.
Environmental Earth Sciences | Year: 2016

The main objective of this study is to propose and verify a novel ensemble methodology that could improve prediction performances of landslide susceptibility models. The proposed methodology is based on the functional tree classifier and three current state-of-the art machine learning ensemble frameworks, Bagging, AdaBoost, and MultiBoost. According to current literature, these methods have been rarely used for the modeling of rainfall-induced landslides. The corridor of the National Road 32 (Vietnam) was selected as a case study. In the first stage, the landslide inventory map with 262 landslide polygons that occurred during the last 20 years was constructed and then was randomly partitioned into a ratio of 70/30 for training and validating the models. Second, ten landslide conditioning factors were prepared such as slope, aspect, relief amplitude, topographic wetness index, topographic shape, distance to roads, distance to rivers, distance to faults, lithology, and rainfall. The model performance was assessed and compared using the receiver operating characteristic and statistical evaluation measures. Overall, the FT with Bagging model has the highest prediction capability (AUC = 0.917), followed by the FT with MultiBoost model (AUC = 0.910), the FT model (AUC = 0.898), and the FT with AdaBoost model (AUC = 0.882). Compared with those derived from popular methods such as J48 decision trees and artificial neural networks, the performance of the FT with Bagging model is better. Therefore, it can be concluded that the FT with Bagging is promising and could be used as an alternative in landslide susceptibility assessment. The result in this study is useful for land use planning and decision making in landslide prone areas. © 2016, Springer-Verlag Berlin Heidelberg. Source

Nakano N.,Kyushu University | Osanai Y.,Kyushu University | Van Nam N.,Vietnam Institute of Geosciences and Mineral Resources
Journal of Mineralogical and Petrological Sciences | Year: 2016

We report first finding of low-temperature eclogite-facies metamorphism from the Red River shear zone in northern Vietnam that has been known as the Paleogene high-temperature metamorphic belt. The rock is extremely aluminous (50.13 wt% Al2O3) and oxidized [Fe3+/(Fe3+ + Fe2+) = 0.89] emery-type rock. Its composition is also characterized by very low SiO2, CaO, and Na2O with high concentrations in high field strength elements, suggesting that the protolith is lateritic bauxite. The analyzed rock is composed mainly of porphyroblastic titanomaghemite, kyanite, allanite, and chloritoid with abundant fine-grained corundum in the matrix. The mineral paragenesis and phase equilibria modeling suggest that the aluminous rock underwent a clockwise pressure-temperature trajectory with the peak metamorphic condition corresponding to low-temperature eclogite- facies approximately 520-550 °C at 1.2-1.5 GPa. Monazite U-Th-Pb dating constrains the timing of the metamorphism to be older than 214 Ma. Our results require two geological events; 1) tropical weathering and bauxitization on the erosional surface, and 2) pre-Late Triassic subduction of supracrustal materials most likely during the Permo-Triassic collisional events in East and Southeast Asia. Our study provides the first evidence for the subduction of supra-continental crustal materials up to 40-50 km depth during the collision between the Indochina and South China blocks. Source

Khoi N.N.,Hanoi University of Science | Hauzenberger C.A.,University of Graz | Tuan D.A.,DOJI Gold and Gems Group | Hager T.,Johannes Gutenberg University Mainz | And 2 more authors.
Neues Jahrbuch fur Mineralogie, Abhandlungen | Year: 2016

Corundum deposits and occurrences are typically associated with marbles in northern Vietnam. Relatively little attention has been paid to corundum hosted by partly migmatized gneisses and pegmatoids of the Day Nui Con Voi range, Ailao Shan-Red River shear zone, North Vietnam. The partly migmatized gneisses contain gray, grayish white to bluish, and yellowish gray sapphires (type 1) while dark red to pinkish rubies occur in feldspathic pegmatoid rocks (type II). Corundum crystals from both types are short prismatic with partly hexagonal tabular shape considerably varying in size. Common inclusions are ilmenite, magnetite, rutile, plagioclase, muscovite, biotite, apatite, zircon, boehmite and iron stains. Growth structures and deformed twinning with star effect can be observed as well. Type I corundum is noted for high content of total Fe (5500 to 7133 ppm), low content of Cr and Ti (59 to 65 and 40 to 58 ppm, respectively), whereas, in corundum of type II the Fe and Cr contents are medium (1028 and 940 ppm, respectively), with low content of Ti (42 ppm). Gneisses hosting type I corundum are characterized by three different mineral parageneses (1) sillimanite+corundum+K-feldspar+biotite; (2) sillimanite+garnet+spinel+corundum+biotite+K-feldspar+plagioclase+ilmenite, and (3) sillimanite+garnet+spinel+corundum+clinopyroxene+ilmenite. Type II corundum occurs in feldspathic pegmatoid rocks consisting of a paragenesis garnet+biotite+plagioclase+K-feldspar+corundum. Sapphire in gneisses (type I) crystallized during regional metamorphism of silica undersaturated metapelites and metapsammites at upper amphibolite to lower granulite facies conditions. Ruby found in desilicated feldspathic rocks (type II) probably formed at the contact of migmatitized pegmatoid bodies with either metabasic to metaultrabasic rocks or marbles. The metamorphic P-T condition of corundum formation was estimated with 650 to 760 °C and 5.0 to 7.6 kbar based on thermobarometric calculations. 40K/40Ar cooling ages obtained from biotite in gneisses indicate that the rocks reached ∼300 °C at ∼23 Ma. © 2016 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany. Source

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