现行黄河口水下三角洲海底形貌及不稳定性   总被引：4，自引：0，他引：4  

杨作升  G.H.Keller  陆念祖  D.B.Prior  林天充  B.D.Bornhold  许卫东  L.D.Wright  J.Suhayda  曹立华  W.J.Wisenman 《中国海洋大学学报(自然科学版)》1990,(1)

高分辨力的声学仪器调查表明,现行黄河口水下三角洲海底的形貌十分复杂,由于高浓度巨量黄河泥沙快速沉积的结果,使河口底坡出现了大量的不稳定性现象,如塌陷冲沟,高密度沉积物重力流,切割—充填结构海底,V形水下河谷、滑塌等。根据海底扰动程度作了分区,划分了地形单元,并对不同的海底形态的成因作了分析。比较了1985和1986年两个航次考查结果的变动,分析了原因。  相似文献   

Fluid evolution and thermal structure in the rapidly exhuming gneiss complex of Namche Barwa–Gyala Peri, eastern Himalayan syntaxis     

D. CRAW  P. O. KOONS  P. K. ZEITLER  W. S. F. KIDD 《Journal of Metamorphic Geology》2005,23(9):829-845

High‐grade gneisses (amphibolite–granulite facies) of the Namche Barwa and Gyala Peri massifs, in the eastern Himalayan syntaxis, have been unroofed from metamorphic depths in the late Tertiary–Recent. Rapid exhumation (2–5 mm year^?1) has resulted in a pronounced shallow conductive thermal anomaly beneath the massifs and the intervening Tsangpo gorge. The position of the 300 °C isotherm has been estimated from fluid inclusions using CO₂–H₂O immiscibility phase equilibria to be between 2.5 and 6.2 km depth below surface. Hence, the near‐surface average thermal gradient exceeds 50 °C km^?1 beneath valleys, although the thermal gradient is relatively lower beneath the high mountains. The original metamorphic fluid in the gneisses was >90% CO₂. This fluid was displaced by incursion of brines from overlying marine sedimentary rocks that have since been largely removed by erosion. Brines can exceed 60 wt% dissolved salts, and include Ca, Na, K and Fe chlorides. These brines were remobilized during the earliest stages of uplift at >500 °C. During exhumation, incursion of abundant topography‐driven surface waters resulted in widespread fracture‐controlled hydrothermal activity and brine dilution down to the brittle–ductile transition. Boiling water was particularly common at shallow levels (<2.5 km) beneath the Yarlung Tsangpo valley, and numerous hot springs occur at the surface in this valley. Dry steam is not a major feature of the hydrothermal system in the eastern syntaxis (in contrast to the western syntaxis at Nanga Parbat), but some dry steam fluids may have developed locally.  相似文献   

Palæohydrology of the calcsilicate aureole of the Beinn an Dubhaich granite, Skye, Scotland: a stable isotopic study     

M. B. HOLNESS  & A. E. FALLICK 《Journal of Metamorphic Geology》1997,15(1):71-83

The contact aureole developed in siliceous carbonates surrounding the Beinn an Dubhaich granite, Skye, shows textural and stable isotope evidence for infiltration of aqueous fluids during both prograde and retrograde metamorphism. Strongly depleted isotope compositions of reaction-product calcite correlate with high silica and fluorine contents, demonstrating a strong link between isotopic alteration and metasomatism by fluids with a significant magmatic component, even at the margins of the aureole. The oxygen and carbon isotope compositions of the carbonates form a linear cluster with a positive slope of about five, consistent with the depletion of isotope compositions by the infiltration of magmatic and/or meteoric fluids. Rayleigh fractionation during devolatilization played a minor role in determining the final isotope composition. Stable isotope compositions of coexisting calcite–dolomite pairs show varying amounts of isotopic disequilibrium, which correlate with the inferred fluid infiltration mechanism. Much of the calcite in dolostones is the product of infiltration-driven reactions along fractures, and is greatly depleted isotopically relative to the host dolomite, especially at talc grade. At higher grades the calcite–dolomite fractionation is smaller, probably due to both increased fluid–rock interaction and a greater tendency for fluid infiltration to be pervasive on the grain-scale. Limestones generally show near-equilibrium fractionation of oxygen and carbon owing to the overwhelming compositional influence of the host calcite. Veins formed during late-stage hydrothermal circulation have strongly ¹⁸O-depleted compositions relative to the host rock. No small-scale spatial patterns to the isotopic depletion were observed, but the extent of fluid infiltration was greatest in the west of the aureole. Fluid infiltration was clearly highly heterogeneous, with no evidence of a consistent flow direction. It is not possible to determine fluid fluxes or flow directions from one-dimensional flow models based on continuum flow in the Beinn an Dubhaich aureole.  相似文献   

A laboratory investigation of the leaching of solute from snowpack by rainfall     

M. Tranter  S. Tsiouris  T. D. Davies  H. G. Jones 《水文研究》1992,6(2):169-178

Under controlled laboratory conditions, artificial rain leaches solute from snow columns, and gives rise to leachate with a composition similar to snowmelt, in addition to the solute initially present in the artificial rain. the initial concentration of ions in the leachate, normalized to the concentration of ions found in the original snow and corrected for the solute present in the artificial rain, is similar to those reported in other laboratory and field studies of snowmelt composition, but there is some evidence that the concentration of leached ions declines more rapidly than during snowmelt. Similarly, as in snowmelt studies, not all ions are leached with the same efficiency. Bearing in mind the confounding influences of snow crystal morphology and snow column hydrology, it seems likely that rain will leach solute from snowpack during rain-on-snow events, in a manner similar to leaching by snowmelt, and that the precise composition of the leachate will depend on the hydrological routing of rain-meltwater mixtures through the snowpack.  相似文献   

东秦岭二郎坪群硅质岩热水沉积地球化学特征及其地质意义   总被引：3，自引：2，他引：3  

冯胜斌  周洪瑞  燕长海  彭翼  袁效奇  贺静 《沉积学报》2007,25(4):564-573

二郎坪群硅质岩成因研究对二郎坪群的构造背景和铜多金属矿床成因的确定具有重要意义。通过对二郎坪群中三种硅质岩的地质特征和岩石地球化学分析，认为二郎坪群硅质岩是典型的热水沉积硅质岩。常量元素地球化学特征值（N(Al)/N（Al+Fe+Mn））指示该硅质岩的沉积环境存在东西差异，南阳盆地以东弧后盆地的规模较大（N(Al)/N（Al+Fe+Mn）=0.30~0.45），沉积环境类似远洋盆地，硅质岩的热液成分比例大，受陆缘物质影响小；而南阳盆地以西弧后盆地的规模较小（N(Al)/N（Al+Fe＋Mn）=0.59），沉积环境为近大陆的边缘海，硅质岩Al含量相对较高，受到陆缘物质影响相对大。地质特征和稀土元素特征（负Eu异常、弱负Ce异常）揭示了二郎坪群硅质岩是弧后盆地型低温热液流体和海水混合形成，这为二郎坪群形成于弧后盆地构造环境的认识提供了新的重要证据。热水沉积硅质岩与铜多金属矿床的共生关系证明研究区铜金属矿床的成因是海底热液喷流沉积作用。  相似文献   

现代海底热液活动调查研究技术进展   总被引：4，自引：1，他引：4  

翟世奎  李怀明  于增慧  于新生 《地球科学进展》2007,22(8):769-776

现代海底热液活动涉及到高温高压环境，异常的热液环境使得传统的深海调查研究方法已远不能满足热液活动研究的需要。直视采样技术、深潜器技术、定点监测技术、保真采样技术及模拟实验技术等成为近年来国内外致力发展的热液活动调查研究技术。在分析了近年来国内外海底热液活动调查研究技术发展的基础上，指出了目前已有技术开发中存在的不足,并且提出了我国在现代海底热液活动技术发展的迫切性和应优先发展的技术。   相似文献   

青海省乌兰乌珠尔斑岩铜矿床地质特征与成因   总被引：26，自引：0，他引：26       下载免费PDF全文

佘宏全张德全  景向阳关 军朱华平  丰成友李大新 《中国地质》2007,34(2):306-314

乌兰乌珠尔斑岩铜矿位于柴达木盆地西缘,为受花岗斑岩脉控制的斑岩型铜矿。岩石化学、稀土和微量元素特征表明:控矿花岗斑岩与围岩(似斑状)斜长花岗岩为钙碱性系列,具轻稀土富集、显著的δEu负异常和Sr、Ba、Ca亏损特征,形成于同碰撞造山环境,与华力西晚期—印支期松潘—甘孜古特提斯洋俯冲碰撞闭合有关。控矿花岗斑岩及其围岩热液蚀变强烈,显示良好的蚀变分带。主要蚀变有钾硅化、绢英岩化和青磐岩化,控矿斑岩内部为钾化和硅化叠加绢英岩化带,近斑岩两侧围岩为绢英岩化带,外侧为青磐岩化带。铜矿化强度与蚀变强度有显著正相关关系。铜矿体空间分布、产状及规模受控矿花岗斑岩体控制。矿床的矿物组合、热液蚀变、硫、氧同位素和流体包裹体测温结果显示矿床形成于中高温环境,流体和成矿物质主要来源于岩浆,乌兰乌珠尔铜矿属与高中温岩浆热液作用有关的斑岩型铜矿。  相似文献   

陕西凤县铁炉湾铅锌矿地质特征及找矿意义     

高卫宏  陈明寿 《西北地质》2007,40(B07):18-22

铁炉湾铅锌矿位于银洞梁-铅硐山次级热水盆地东北端，具有形成“热水喷流沉积-改造型”铅锌矿床的有利成矿环境，矿床赋存于星红铺组第3岩性段中部，矿体受结晶灰岩、结晶白云岩及层间断裂控制。已发现的矿体具有一定的规模，且有向深部变好的趋势，物化探异常亦显示其深部找矿前景较好。在凤太矿田泥盆纪次级热水沉积盆地中已发现3个赋矿层位。以往的铅锌找矿工作都是以古道岭组灰岩与星红铺组千枚岩接触带为主要勘查对象，而没有对星红铺组中的铅锌矿勘查引起足够的重视，铁炉湾铅锌找矿工作的不断加强，将会取得较好的成果，进而开展在广泛分布的星红铺组第三岩性段中寻找铅锌矿的工作。  相似文献   

三江平原典型湿地系统大气湿沉降中氮素动态及其生态效应   总被引：3，自引：0，他引：3       下载免费PDF全文

孙志高  刘景双  王金达 《水科学进展》2007,18(2):182-192

2004年7月至2005年6月对三江平原典型湿地系统大气湿沉降中的氮素动态进行了研究,并探讨了其生态效应。结果表明,各形态氮月均浓度之间差别较大,具有明显的季节性,原因主要与人类活动、降水强度及频次、风向、地理位置以及氮氧化物自然排放有关;湿沉降的TN组成以TIN为主(51.38%~98.96%),TIN又以NH₄+-N和NO₃--N特别是NH₄+-N为主,降水天气系统的路径在很大程度上影响着降水中各形态氮的组成;降水量与各形态氮浓度均呈较弱的负相关(p>0.05),而NH₄+-N与NO₃--N、TON均呈显著正相关(p<0.05),它们可能具有同源性。NH₄+-N与NO₃--N的良好相关性与其在液相中的反应有关;生长季是全年氮沉降的重要时期,其TN沉降量为非生长季的1.84倍,二者所占比例分别为64.78%和35.22%。除NO₂--N外,其它各形态氮的沉降量均以生长季为主体;全年TN沉降量为7.57 kg/hm2,TIN/TON之比为5.47,TIN为沉降主体,占84.56%。NH₄+-N和NO₃--N是TIN沉降的主体,其所占全年的比例分别为52.55%和30.03%;氮是该区植物生长的限制因素,生长季的氮沉降对于促进植物生长直接生态意义重大,而非生长季的氮沉降对于大量补充次年植物生长初期所需养分的间接生态意义明显,其生态作用不容忽视;近年来湿地系统氮沉降量的降低可能是导致其退化的重要原因,其生态影响也不容忽视。  相似文献   

Geology and geochemistry of giant quartz veins from the Bundelkhand Craton,central India and their implications   总被引：1，自引：0，他引：1  

J. K. Pati  S. C. Patel  K. L. Pruseth  V. P. Malviya  M. Arima  S. Raju  P. Pati  K. Prakash 《Journal of Earth System Science》2007,116(6):497-510

Giant quartz veins (GQVs; earlier referred to as ‘quartz reefs’) occurring in the Archean Bundelkhand Craton (29,000 km²) represent a gigantic Precambrian (∼2.15 Ga) silica-rich fluid activity in the central Indian shield. These veins form a striking curvilinear feature with positive relief having a preferred orientation NE-SW to NNE-SSW in the Bundelkhand Craton. Their outcrop widths vary from ≤1 to 70m and pervasively extend over tens of kilometers along the strike over the entire craton. Numerous younger thin quartz veins with somewhat similar orientation cut across the giant quartz veins. They show imprints of strong brittle to ductile-brittle deformation, and in places are associated with base metal and gold incidences, and pyrophyllite-diaspore mineralization. The geochemistry of giant quartz veins were studied. Apart from presenting new data on the geology and geochemistry of these veins, an attempt has been made to resolve the long standing debate on their origin, in favour of an emplacement due to tectonically controlled polyphase hydrothermal fluid activity.  相似文献