Physical constraints on impact melt properties from Lunar Reconnaissance Orbiter Camera images     

Brett W. Denevi  Steven D. Koeber  Mark S. Robinson  W. Brent Garry  B. Ray Hawke  Thanh N. Tran  Samuel J. Lawrence  Laszlo P. Keszthelyi  Olivier S. Barnouin  Carolyn M. Ernst  Livio L. Tornabene 《Icarus》2012,219(2):665-675

Impact melt flows exterior to Copernican-age craters are observed in high spatial resolution (0.5 m/pixel) images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). Impact melt is mapped in detail around 15 craters ranging in diameter from 2.4 to 32.5 km. This survey supports previous observations suggesting melt flows often occur at craters whose shape is influenced by topographic variation at the pre-impact site. Impact melt flows are observed around craters as small as 2.4 km in diameter, and preliminary estimates of melt volume suggest melt production at small craters can significantly exceed model predictions. Digital terrain models produced from targeted NAC stereo images are used to examine the three-dimensional properties of flow features and emplacement setting, enabling physical modeling of flow parameters. Qualitative and quantitative observations are consistent with low-viscosity melts heated above their liquidii (superheated) with limited amounts of entrained solids.  相似文献   

Origin and extent of fresh groundwater, salty paleowaters and recent saltwater intrusions in Red River flood plain aquifers, Vietnam   总被引：1，自引：0，他引：1  

Luu T. Tran  Flemming Larsen  Nhan Q. Pham  Anders V. Christiansen  Nghi Tran  Hung V. Vu  Long V. Tran  Hoan V. Hoang  Klaus Hinsby 《Hydrogeology Journal》2012,20(7):1295-1313

A model has been established on the origin and extent of fresh groundwater, salty paleowaters and saltwater from recent seawater intrusions in the Red River flood plain in Vietnam. This was done with geological observations, geophysical borehole logging and transient electromagnetic methods. Salt paleowater is present up to 50–75?km from the coastline, with occurrence controlled by the Holocene transgression. A density-driven leaching of salty porewater has occurred from high-permeability Holocene sediments into underlying Pleistocene deposits, whereas diffusion has dominated in low-permeability layers. In the Pleistocene aquifer, the highest content of dissolved solids is found below two intrinsic valleys with Holocene marine sediments and along the coastline. Recent intrusion of saltwater from the South China Sea is observed in shallow groundwater 35?km inland, probably a result of transport of salty water inland in rivers or leaching of paleowaters from very young near-coast marine sediments. The observed inverted salinity profile, with high saline water overlying fresher groundwater, has been formed due to the global eustatic sea-level changes during the last 8,000–9,000?years. The proposed model may therefore be applicable to other coastal aquifers, with a proper incorporation of the local geological environments.  相似文献   

Complex deposits in the Lo Gam structure,northeastern Vietnam: mineralogy,geochemistry, and formation conditions     

Tran Tuan Anh  I.V. Gas’kov  Tran Trong Hoa  P.A. Nevol’ko  Pham Thi Dung  Pham Ngoc Can 《Russian Geology and Geophysics》2012,53(7):623-635

The Pb–Zn deposits in the Lo Gam structure, northeastern Vietnam, account for>80% of all the Pb and Zn resources of Vietnam. All the deposits make up four isolated ore districts (Thai Nguyen, Cho Don, Cho Dien, Na Son), which can be combined in one metallogenic zone extending for >100 km from southeast to northwest. The Pb–Zn deposits in all the ore districts show some similarity to stratiform (Mississippi-type) deposits: confinement to Devonian carbonate sediments; localization at the intersection of faults of different orientations; vein and stockwork (pocket-vein-disseminated) morphology of the mineralized zones; evidence for hydrothermal-metasomatic formation (carbonate-rock marbleization, quartz–carbonate veins, etc.); and low and moderate mineralization temperatures (<250 °C). On the other hand, some differences from stratiform deposits are observed: widespread occurrence of Permo-Triassic igneous rocks in the above ore districts; absent tabular orebodies, which are typical of stratiform deposits; large set of trace elements (In, Bi, Sb, Au, Ag, Cu, Cd) not typical of stratiform deposits; and an endogenic primary source, as evidenced by the isotope composition of sulfur (δS³⁴= 2.68‰), which is close to meteoritic, and the set of trace elements, which are mainly of deep genesis. All this indicates that the above Pb–Zn deposits within the carbonate units are low-and moderate-temperature hydrothermal-metasomatic products associated with active magmatism which took place in this region in the Permo-Triassic.The differences in the mineral composition of the deposits, as well as in the trace-element set and contents at different deposits, clearly indicate an intricate ore formation process and the relation of the deposits with magmatism of different compositions. The simple mineral composition and the limited set of trace elements (Cd, Ag, Sb, As) at the Lang Hich deposit are closer to the characteristics of stratiform deposits. Also, manifestations of magmatism are almost absent here. On the contrary, unusually high (ppm) In (75.8), Sn (307.5), Cu (1080), Ag (157.7), Bi (99), and As (13,650) contents were observed at the deposits of the Cho Don and Cho Dien districts, with widespread granitoid magmatism in the Phia Bioc complex. Rare-earth mineralization (orthite) and high Mo, Re, and Rb contents at the deposits of the Na Son district are probably due to the widespread occurrence of stratified alkaline volcanics and their subvolcanic analogs, which belong to the Pla Ma complex (ξγPZ₂ pm).  相似文献   

K-Ar Dating of Fault Gouges from the Red River Fault Zone of Vietnam   总被引：1，自引：0，他引：1  

BUI Hoang B  NGO Xuan Thanh  Yungoo SONG  Tetsumaru ITAYA  Koshi YAGI  KHUONG The Hung  NGUYEN Tien Dung 《《地质学报》英文版》2016,90(5):1653-1663

Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes.This paper presents the first authigenic illite K-Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province,Vietnam.The fault gouge samples were separated into three grain-size fractions(0.1 μm,0.1-0.4 μm and 0.4-1.0 μm).The results show that the K-Ar age values decrease from coarser to finer grain fractions(24.1 to 19.2 Ma),suggesting enrichment in finer fraction of morerecently grown authigenic illites.The timing of the fault movement are the lower intercept ages at 0%detrital illite(19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma).In combination with previous geochronological data,this result indicates that the metamorphism of the Day Nui Con Voi(DNCV) metamorphic complex took place before ca.26.8 Ma.At about 26.8 Ma-25 Ma,the fault strongly acted to cause the rapid exhumation of the rocks along the Red River-Ailoa Shan Fault Zone(RR-ASFZ).During brittle deformation,the DNCV slowly uplifted,implying weak movement of the fault.This brittle deformation might have lasted for ca.5 Ma.  相似文献   

Triggered earthquake study in Tranh River No. 2 (Vietnam) Hydropower Reservoir     

Cao Dinh Trieu  Cao Dinh Trong  Le Van Dung  Thai Anh Tuan  Dinh Quoc Van  Ha Vinh Long 《Journal of the Geological Society of India》2014,84(3):319-325

This article presents the results of investigating triggered earthquakes in the vicinity of Tranh River No.2 Hydropower Reservoir in recent years. It is found that earthquakes occurred in the vicinity of Tranh River Hydropower Reservoir, probably associated with the Trà My — Trà BÓng fault zone. It is estimated that this fault is capable of hosting an earthquake of M~6.1. The ‘b’ value for this earthquake sequence is 0.83, which is higher than the regional ‘b’ value of 0.60. We estimate that the return period of earthquakes of M=4.5, 5.0, 5.5 and 6.0 is 11, 29, 76 and 198 months respectively. On October 22, 2012 an earthquake M_S=4.6, I₀=6.0 (MSK-64) occurred at 13:41:28 hrs GMT. The epicenter of the earthquake was located at a distance of 5.5 km away from the center of the dam towards the west. The focal depth is about 4.5 km, and the rupture length is about 1.8 km.  相似文献   

黑龙江三道湾子碲化物型金矿床流体包裹体及硫同位素研究   总被引：6，自引：3，他引：3  

赵胜金  刘俊来  白相东  赵海滨  吕军  陈越  陈美勇 《矿床地质》2010,29(3):476-488

三道湾子金矿床是新近发现的一个典型的碲化物型浅成热液金矿床,金银以碲化物形式赋存于石英脉中.含矿石英脉中石英内流体包裹体的主要类型为液体包裹体,其气相分数大多集中在5%～15%.对应于早矿化阶段、主成矿阶段、晚矿化阶段的流体包裹体的均一温度分别为230～396℃;220～320℃(峰值260～280℃);140～300℃(峰值180～240℃).激光拉曼探针原位成分分析表明,各阶段流体包裹体的气、液相成分主要为H2O,部分气相含有甲烷、丙烷、丁炔等烃类;主成矿阶段的纯气体包裹体的成分为甲烷,其次为丙烷、丁炔等,可能是深源流体的启示.δ34S值在0附近,为较小的正值或负值,具有地幔硫的特征.上述分析揭示出,三道湾子金矿床是中低温热液矿床.伴随着早白垩世区域伸展作用期间的亚碱性火山作用,深源流体与大气水混合,促使热液携带的成矿物质在浅部地壳卸载、沉淀和结晶,并以裂隙充填占主导的成矿作用方式多阶段成矿.  相似文献   

Selective separation of very fine particles at a planar air–water interface     

Diana N.H. Tran  Catherine P. Whitby  Daniel Fornasiero  John Ralston 《International Journal of Mineral Processing》2010,94(1-2):35-42

Selective fine particle separation is a key unit operation in the mineral and related industries. In flotation, the capture of fine particles by bubbles is inefficient due to their low mass and momentum, which result in low particle–bubble collision efficiency. We demonstrate that it is possible to selectively separate a mixture of very fine hydrophobic graphite and hydrophilic quartz particles by direct contact with an air–water interface without a particle–bubble collision step involved. We demonstrate that it is possible to scale-up the process from a simple batch to a continuous process. Good selective separation of graphite from quartz gangue could be obtained under continuous conditions.  相似文献   

The conditions of formation of sapphire and zircon in the areas of alkali-basaltoid volcanism in Central Vietnam     

A.E. Izokh  S.Z. Smirnov  V.V. Egorova  Tran Tuan Anh  S.V. Kovyazin  Ngo Thi Phuong  V.V. Kalinina 《Russian Geology and Geophysics》2010,51(7):719-733

Study of the chemical composition of clinopyroxene and garnet megacrysts from the Dak Nong sapphire deposit and model calculations have shown that megacrysts originated from the crystallization of alkali basaltoid magma in a deep-seated intermediate chamber at 14–15 kbar, which is close to the Moho depth (50 km) in this part of southeastern Asia. The chamber was a source of heat and CO₂ fluids for the generation of crustal syenitic melts producing sapphires and zircons. The formation conditions of sapphires and zircons are significantly different. The presence of jadeite inclusions in placer zircons points to high pressures during their crystallization, which is confirmed by the ubiquitous decrepitation of CO₂-rich melt inclusions. Sapphires crystallized from iron-rich syenitic melt in the shallower Earth’s crust horizons with the participation of CO₂ and carbonate–H₂O–CO₂ fluids. The subsequent eruptions of alkali basalts favored the transportation of garnet and pyroxene megacrysts as well as sapphire and zircon xenocrysts to the surface. It is shown that sapphire deposits can be produced only during multistage basaltic volcanism with deep-seated intermediate chambers in the regions with thick continental crust. The widespread megacryst mineral assemblage (clinopyroxene, garnet, sanidine, ilmenite) and the presence of placer zircon megacrysts can be used as indicators for sapphire prospecting.  相似文献