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1.
D. A. Novikov Doan Van Tuyen Thi Kim Van Phan N. A. Kharitonova 《Russian Journal of Pacific Geology》2018,12(1):63-79
The results of studying the features of the hydrogeological structure and chemical and isotope composition of thermal waters from the central part of Vietnam that are characterized by intense manifestations of intrusive magmatism are presented. It is established that low–and high–thermal waters with temperature varying within 30–85°C are developed in the area under study. The value of total mineralization of the hydrotherms ranges from 0.05 to 10.05 g/dm3. It is assumed that the circulation of thermal waters that are different in temperature and chemical composition occurs at two levels. The regular change of the hydrotherm composition in the direction from mineralized chloride sodium, including with increased Ca content, to fresh sodium bicarbonate is revealed. The ratio of δ18O–δ2H isotopes indicates that the water component is based on meteoric water. In the coastal areas, there is an isotope shift towards the ocean waters, which is also confirmed by the hydrogeochemical data. The key factors for forming the chemical composition of the thermal waters in South Trungbo are their genetic type, the interaction processes in the “water–rock–gas–organic substance” system, and their equilibrium–nonequilibrium state. 相似文献
2.
Doan Aydal 《地学学报》1990,2(1):43-52
The mineralogy and chemistry of gold-bearing listwaenites of Gemiköy in the Araç massif (southern part of the Daday-Devrekâni massif) were investigated in detail. The process of listwaenitization and the reasons for gold enrichment in the area are discussed. The listwaenites have no direct contact with any magmatic intrusion or extrusion. Detailed chemical analysis showed that the listwaenitized rocks contain silica-, silica and carbonate-, and carbonate-rich parts. Each part is different chemically from the others, even in terms of accessory mineral content. In general, the listwaenites differed chemically and mineralogically from the surrounding ultramafic rocks. In particular, SiO2 and CaO contents of listwaenites were higher and MgO and Al2O3 contents were lower than in the surrounding ultramafic rocks. Furthermore, Ni, As, Mn, Zn, Pb and Co enrichment occurred during listwaenitization, while K was absent and Ni enrichment was detected especially in silica and carbonate-, and carbonate-rich parts. Finally, Gemiköy listwaenites are interpreted as autometamorphic, even though they show similarities to allometamorphic listwaenites according to Ploshko's (1963) classification. 相似文献
3.
Liu Jiandong Doan Chi Dung Liong Shie-Yui Sanders Richard Dao Anh Tuan Fewtrell Timothy 《Natural Hazards》2015,75(2):1075-1104
Natural Hazards - Jakarta is vulnerable to flooding and extreme rainfall events are always the main cause of the occurrence of heavy flood events with loss of life and property. The flood in... 相似文献
4.
Doan Van Binh Sameh A. Kantoush Tetsuya Sumi Nguyen Phuong Mai Trieu Anh Ngoc La Vinh Trung Tran Dang An 《水文研究》2021,35(2):e14030
The hydrogeomorphology of the Vietnamese Mekong Delta (VMD) has been significantly altered by natural and anthropogenic drivers. In this study, the spatiotemporal changes of the flow regime were examined by analysing the long-term daily, monthly, annual and extreme discharges and water levels from 1980 to 2018, supported by further investigation of the long-term annual sediment load (from the 1960s to 2015), river bathymetric data (in 1998, 2014 and 2017) and daily salinity concentration (from the 1990s to 2015) using various statistical methods and a coupled numerical model. Then, the effects of riverbed incision on the hydrology were investigated. The results show that the dry season discharge (i.e., in March–June) of the Tien River increased by up to 23% from the predam period (1980–1992) to the postdam period (1993–2018) but that the dry season water level at My Thuan decreased by up to −46%. The annual mean and monthly water levels in June at Tan Chau and in January and June–October at My Thuan in the Tien River decreased statistically, even though the respective discharges increased significantly. These decreased water levels instead of the increased discharges were attributed to the accelerated riverbed incision upstream from My Thuan, which increased by more than three times, from a mean rate of −0.16 m/year (−16.7 Mm3/year) in 1998–2014 to −0.5 m/year (−52.5 Mm3/year) in 2014–2017. This accelerated riverbed incision was likely caused by the reduction in the sediment load of the VMD (from 166.7 Mt/year in the predam period to 57.6 Mt/year in the postdam period) and increase in sand mining (from 3.9 Mm3 in 2012 to 13.43 Mm3 in 2018). Collectively, the decreased dry season water level in the Tien River is likely one of the main causes of the enhanced salinity intrusion. 相似文献
5.
Toshifumi Komatsu Ryota Urakawa Toshitaka Inada Kazuki Yamauchi Takumi Maekawa Reishi Takashima Mark Williams Phong D. Nguyen Hung D. Doan Minh T. Nguyen Shuji Niko Gengo Tanaka Tatsuhiko Yamaguchi 《Island Arc》2019,28(1)
Upper Devonian carbonates of the Toc Tat Formation in the Si Phai Pass area of Dong Van District, northern Vietnam were deposited in carbonate platform, slope, and basin environments. These carbonates yield abundant conodonts indicative of the Palmatolepis nasuta, Pa. linguiformis and Pa. triangularis zones, the Frasnian–Famennian stage boundary being identified by the first occurrence of Pa. triangularis. Two positive carbon isotope excursions are recognized, the lower excursion peaking in the interval of the lower to middle Pa. nasuta Zone, whilst the upper excursion peaks just above the local Frasnian–Famennian boundary. Based on the biostratigraphy, these excursions equate to the Lower and Upper Kellwasser events. Locally, tentaculitoid taxa (Nowakia, Styliolina, Homoctenus, and Metastyliolina?) are abundant in the interval of the Pa. nasuta Zone, but show a drastic decline in abundance before the Lower Kellwasser Event, and only two taxa survived into the Famennian. 相似文献
6.
Numerous tholeiitic mafic-ultramafic intrusions occurring in the Avalon and the Gander terranes of the Appalachian Orogen host magmatic Ni-Cu sulfide accumulations. The sulfide occurrences of the Gander terrane are depleted in the platinum-group elements (PGE). Total PGE abundances in these intrusions do not exceed several hundreds of ppb. The Mechanic intrusion occurring in the Avalon terrane, on the other hand, has PGE concentrations as high as 2400 ppb. Low PGE levels in the Gander terrane can be explained by equilibration of the immiscible sulfide melt with a low proportion of silicate magma. One possible explanation would be that the parental magmas for these intrusions were sulfur saturated before leaving their source region. An early sulfide fractionation during migration to the upper crustal levels, or immediately after entering the magma chamber is another possibility. Differences in the PGE geochemistry of the two groups can be explained by the different source region characteristics and different environments in which the magmas evolved. 相似文献
7.
Catherine Noiriel François Renard Mai-Linh Doan Jean-Pierre Gratier 《Chemical Geology》2010,269(3-4):197-209
Mineral precipitation in the pores of a rock may exert a force, which is called crystallization pressure. This process has been studied experimentally and results bring a new look on the way fractures may develop and seal in natural systems. Cylindrical core samples of porous limestone and sandstone were left for several weeks in contact with an aqueous solution saturated with sodium chloride, at 30 or 45 °C, under axial normal stress in the range 0.02–0.26 MPa. The fluid was allowed to rise in the core samples by capillary forces, up to a controlled height where evaporation and precipitation occurred. The uniaxial deformation of the samples was measured using high-resolution displacement sensors. The samples were characterized using computed X-ray tomography, allowing therefore imaging in 3D the intensity and localization of the damage. Two kinds of damage could be observed. Firstly, small rock fragments were peeled from the sample surface. Secondly, and more interestingly, fracture networks developed, by nucleation of microcracks at the interface where evaporation occurred, and propagation to the free surface. Two families of fractures could be identified. A first set of sealed fracture parallel to the evaporation front is directly induced by crystallization pressure. A second fracture network, perpendicular to the evaporation front, accommodates the first set of fractures. An analytical model where fluid flow is coupled to evaporation, vapour transport, and localization of mineral precipitation explains the shape of this fracture network. 相似文献
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9.
Pham Van Tien Kyoji Sassa Kaoru Takara Hiroshi Fukuoka Khang Dang Tatsuya Shibasaki Nguyen Duc Ha Hendy Setiawan Doan Huy Loi 《Landslides》2018,15(9):1761-1778
Extreme heavy rainfall due to Typhoon Talas on September 2–4, 2011 in the Kii Peninsula, Japan, triggered numerous floods and landslides. This study investigates the mechanism and the entire process of rainfall-induced deep-seated landslides forming two massive dams in the Kuridaira and Akatani valleys, respectively. The mechanism of the rapid deep-seated landslides is examined through a series of laboratory experiments on samples from sliding surfaces by using undrained high-stress dynamic-loading ring-shear apparatus. The test results indicate that the failure of samples is triggered by excess pore water pressure generation under a shear displacement from 2 to 7 mm with a pore pressure ratio ranging from 0.33 to 0.37. The rapid movement of landslides is mainly attributed to high mobility due to the liquefaction behavior of both sandstone-rich and shale samples. Geomorphic settings and landslide mobility are major contributing factors to the dam formation. Additionally, shear displacement control tests show that a certain amount of shear displacement between 2 and 7 mm along the sliding surfaces of the gravitationally deformed slopes might have led to the failures. Importantly, computer simulation with LS-RAPID software using input parameters obtained from physical experiments is employed to interpret the entire formation process of the abovementioned two landslide dams. The simulation results are examined in accordance with the observed on-site geomorphic features and recorded data to explain the possibility of sliding processes. The results further point out that local failures are initiated from the lower middle part of the landslide bodies where the geological boundary exists. This condition most probably influences the landslide initiation in the two case studies. This research is therefore helpful for hazard assessment of slopes that are susceptible to deep-seated landslides and other sequential processes in areas with geology and geomorphology similar to that of the Kii Peninsula. 相似文献
10.
Influence of tectonics and neotectonics on the morphogenesis of the peak karst of Halong Bay,Vietnam
Pascal Fenart N. N. Cat Claude Drogue Doan Van Canh Sévenn Pistre 《Geodinamica Acta》2013,26(3-4):193-200
AbstractIn northeast Vietnam, the karst of Halong Bay is characterized by very active neotectonics. The directional distribution of fracturing of the calcareous rocks is characterized by the influence of two major fault zones: the Red River fault zone (N140) and the Tan-Lu fault zone (N050). Karst development was favoured by intense fracturing, according to these two major directions, and reactived during recent tectonics by a compressional regime with σ1 N070, followed by an extensional regimes with σ1 near to EW that led to significant vertical movement. These tectonics, coupled with intense erosion, led to genesis and evolution of the spectacular morphology of this peak karst. © Elsevier, Paris 相似文献