我国第四纪火山活动的板块构造背景     

黄镇国  张伟强 《地理科学》1995,15(2):109-117

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Fractionation of phosphorus in the sediments of a tropical estuary   总被引：3，自引：0，他引：3  

A. N. Balchand  S. M. Nair 《Environmental Geology》1994,23(4):284-294

Fractionation of phosphorus in the sediments of the Cochin estuary situated along the southwest coast of India was studied by applying sequential chemical extraction. The different forms of phosphorus were estimated seasonally (premonsoon, monsoon, and postmonsoon) under eight different schemes. The major forms of phosphorus analyzed were exchangeable P, anion exchangeable P, carbonate-bound P, labile and resistant organic P, Fe and Al P, calcium-bound P, and hydrolyzable surplus P. Quantitatively, the above fractions in isolation or in combination vary in content due to chemoestuarine variability and seasonal fluctuations. Changes in speciation have been noted in association with salinity variations in the waterway, especially following enhanced river runoff during the monsoon. The chemical forms of the sediment-bound phosphorus in the northern parts of this estuary have been shown to be modified by nonpoint sources. Sediment P fractionation defines the role of chemical speciation of phosphates (as nutrients) and is indicative of the processes controlling the pathways of P into the coastal waters. The changes in the exchangeable P, together with marked regional variations in calcium-bound P, exemplify the complex estuarine variability of phosphorus. Enhanced amounts of exchangeable P mark its appearence in high saline waters, signifying the presence of biologically available nutrient phosphorus. The calcium-bound P and hydrolyzable surplus P show significant relation with sediment organic carbon and Fe whereas other forms do not exhibit any marked covariation. The Ca and Na NTA extraction scheme is very specific in its selectivity.  相似文献   

Geothermobarometry of mafic granulites and metapelite from the Palghat Gap, South India: petrological evidence for isothermal uplift and rapid cooling   总被引：1，自引：0，他引：1  

C. R. RAVINDRA. KUMAR  T. CHACKO 《Journal of Metamorphic Geology》1994,12(4):479-492

The Palghat Gap region is located near the centre of the large southern Indian granulite terrane. at the northern edge of the Kodaikanal charnockite massif. The dominant rock types in the region are hornblende-biotite ± orthopyroxene gneisses and charnockites along with minor amounts of intercalated mafic granulite, metapelite and calc-silicate. The P-T estimates from garnetiferous mafic granulites and metapelite samples are generally in the range 9-10 kbar and 800-900 C using both conventional thermobarometric methods and the TWEEQU thermobarometry program. These P-T estimates, which should be taken as minimum values, are among the highest yet reported for South Indian and Sri Lankan granulites. The occurrence of orthopyroxene + plagioclase symplectites around embayed garnet grains in the mafic granulites and cordierite rims around garnet grains in metapelite suggest an isothermal decompression-type path. Similarly, a core-rim P-T trajectory indicates c. 3 and 7 kbar decompression at high temperature in the mafic granulites and metapelite, respectively. In both rock types, the key to the determination of the retrograde P-T path was the recognition of small amounts of second generation plagioclase with a more anorthitic composition than the matrix plagioclase. The preservation of high garnet-pyroxene temperatures in the mafic granulites (despite small garnet grain size) suggests rapid cooling of the terrane. Calculated minimum cooling rates range from 8 to 80 C Ma^-1. Such cooling rates are more rapid than those associated with normal isostatic processes and suggest that the terrane was tectonically exhumed at high temperature.  相似文献   

Fluid inclusions in rocks from the amphibolite-facies gneiss to charnockite progression in southern Karnataka, India: direct evidence concerning the fluids of granulite metamorphism   总被引：2，自引：1，他引：2  

E. C. HANSEN  R. C. NEWTON  A. S. JANARDHAN 《Journal of Metamorphic Geology》1984,2(3):249-264

Abstract Fluid inclusion studies of rocks from the late Archaean amphibolite-facies to granulite-facies transition zone of southern India provide support for the hypothesis that CO₂,-rich H₂O-poor fluids were a major factor in the origin of the high-grade terrain. Charnockites, closely associated leucogranites and quartzo-feldspathic veins contain vast numbers of large CO₂-rich inclusions in planar arrays in quartz and feldspar, whereas amphibole-bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed-facies quarries contain no large fluid inclusions. Inclusions in the northernmost incipient charnockites, as at Kabbal, Karnataka, occasionally contain about 25 mol. % of immiscible H₂O lining cavity walls, whereas inclusions from the charnockite massif terrane farther south do not have visibile H₂O Microthermometry of CO₂ inclusions shows that miscible CH₄ and N₂ must be small, probably less than 10mol.%combined. Densities of CO₂ increase steadily from north to south across the transitional terrane. Entrapment pressures calculated from the CO₂ equation of state range from 5 kbar in the north to 7.5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750°C, in quantitative agreement with mineralogic geobarometry. This agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions. Calculations on the stability of the charnockite assemblage biotite-orthopyroxene-K-feldspar-quartz show that an associated fluid phase must have less than 0.35 H₂O activity at the inferred P and T conditions, which agrees with the petrographic observations. High TiO₂ content of biotite stabilizes it to lower H₂O activities, and the steady increase of biotite TiO₂ southward in the area suggests progressive decrease of aH₂O with increasing grade. Oxygen fugacities calculated from orthopyroxene-magnetite-quartz are considerably higher than the graphite CO₂-O₂ buffer, which explains the absence of graphite in the charnockites. The present study quantifies the nature of the vapours in the southern India granulite metamorphism. It remains to be determined whether CO₂-flushing of the crust can, by itself, create large terranes of largeion lithophile-depleted granulites, or whether removal of H₂O-bearing anatectic melts is essential.  相似文献   

印度与欧亚大陆碰撞构造变形数值分析   总被引：8，自引：0，他引：8  

陈开平  马瑾 《地震地质》1995,17(3):277-284

在全面考虑了大陆构造变形三重非线性特征的基础上，用动态有限元法研究了藏东对印度与欧亚大陆碰撞作用的大变形响应。数值模拟结果显示了明显的纵向收缩变形，变形主轴多具有顺时针转动的趋势，但横向位移在总体上并不显著。其最大值正位于红河和鲜水河断裂之间，这一结果论证了印度板块对欧亚大陆的碰撞可能是川滇菱形块体向南东运动的动力来源。红河、鲜水河、昆仑及阿尔金活断层在碰撞作用下发生了顺时针的旋转变形；而且，计算结果模拟出了红河断裂由左旋变为右旋，另３条断裂始终左旋的运动特征  相似文献   

论板块运动的驱动力          下载免费PDF全文

谢鸣一  谢鸣谦 《地质科学》1987,(3):209-220

本文从动力学的角度讨论了板块运动的驱动机理,并提出了计算板块扩张速度的公式,然后求出了不同类型板块的扩张速度。用此公式所计算出的板块扩张速度与实际观测速度很符合。  相似文献   

Plate tectonics,palaeoenvironments and limestone geomorphology in West-Central Britain     

Ian Douglas 《地球表面变化过程与地形》1987,12(5):481-495

The variety of active, exhumed, and buried limestone landforms of northern England, North Wales, and the Isle of Man arises in part from the way in which Dinantian (Lower Carboniferous) sedimentation was affected by a tilt-block basement structure evolved during the closure of the Iapetus Ocean suture to the north, and partly to subsequent plate tectonic movements associated with the closure of the proto-Tethys ocean, the opening of the Atlantic Ocean and the Alpine orogeny. Landforms created during the Dinantian now form important exhumed and buried landscape features. The Permian half-graben structures of the eastern Irish Sea-Cheshire-Worcester Basins account for many of the contrasts between the upland karsts of the Pennines and the lowland karsts of coastal areas.  相似文献   

A study of tropospheric wave disturbances over India in winter     

I. Subbaramayya  A. S. N. Raju 《Pure and Applied Geophysics》1982,120(3):437-452

The wave disturbances in the troposphere over north and central India during winter when the subtropical westerlies prevail in the upper air over the area have been investigated by power-and cross-spectrum analysis. The power-spectrum study revealed the existence of basically two systems of periods 10.0–12.5 days and 4.5–5.5 days in the middle and upper troposphere. Both the long-and short-period systems have been found to be propagating eastwards at rates 5° and 10° long./day respectively. In both the cases lower temperatures are found to the east of the troughs. It is also noted that these systems build up the meridional temperature gradient and hence strengthen the upper tropospheric westerlies. Synoptic study of the transient systems is presented.  相似文献   

论博格达俯冲撕裂型裂谷的形成与演化   总被引：66，自引：23，他引：43  

顾连兴  胡受奚等 《岩石学报》2001,17(4):585-597

博格达裂谷带位于准噶尔与吐－哈两个前寒武纪地块之间,呈东－西走向,东端与克拉麦里－哈尔里克泥盆－石炭纪火山弧呈大角度相交。该 裂谷于早－中石炭世启动和沉降,在盆地中堆积了巨厚的陆源碎屑岩夹双峰式火山岩。裂谷的闭合发生于中石炭世末至晚石炭世。在裂谷闭合后区域构造由挤压向拉张的转折时期,发生了以辉绿岩为主的侵入活动,并伴有少量中－酸性分异产物。博格达裂谷东、西两段的演化特征有着显著差异。东段早石炭世就已开始裂离,裂离过程的火山岩以玄武岩为主,仅有少量流纹岩,裂谷盆地强烈沉降,形成深海－半深海环境,裂谷在中石炭世末至晚石炭世初即已闭合,裂谷岩系因强烈褶皱,与上覆二叠系呈明显角度不整合,显示了“突变”式闭合特征。与此不同的是,西段至中石炭世才开始明显裂离,裂离过程的火山岩以英安岩和流纹岩为主,玄武岩量较少,火山－沉积岩系均形成于浅海环境,裂谷至晚石炭世末才发生闭合,裂谷岩系因未发生强烈褶皱,故与上覆二叠系为平行不整合接触,显示了“渐变”式闭合特征。该裂谷的形成是古亚洲洋壳向先存的准－吐－哈陆块斜向俯冲,将其东南端撕裂的产物,因而可称为俯冲撕裂型裂谷。演化过程沿走向的明显不均一性是这类裂谷的重要特点。  相似文献   

Challenges of using remote sensing and GIS in developing nations   总被引：2，自引：1，他引：2  

Madan K. Jha  V. M. Chowdary 《Hydrogeology Journal》2007,15(1):197-200

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