A review of crust and upper mantle structure studies of the Snake River Plain-Yellowstone volcanic system: A major lithospheric anomaly in the western U.S.A.

The Snake River Plain-Yellowstone volcanic system is one of the largest, basaltic, volcanic field in the world. Here, there is clear evidence for northeasterly progression of rhyolitic volcanism with its present position in Yellowstone. Many theories have been advanced for the origin of the Snake River Plain-Yellowstone system. Yellowstone and Eastern Snake River Plain have been studied intensively using various geophysical techniques. Some sparse geophysical data are available for the Western Snake River Plain as well. Teleseismic data show the presence of a large anomalous body with low P- and S-wave velocities in the crust and upper mantle under the Yellowstone caldera. A similar body in which compressional wave velocity is lower than in the surrounding rock is present under the Eastern Snake River Plain. No data on upper mantle anomalies are available for the Western Snake River Plain. Detailed seismic refraction data for the Eastern Snake River Plain show strong lateral heterogeneities and suggest thinning of the granitic crust from below by mafic intrusion. Available data for the Western Snake River Plain also show similar thinning of the upper crust and its replacement by mafic material. The seismic refraction results in Yellowstone show no evidence of the low-velocity anomalies in the lower crust suggested by teleseismic P-delay data and interpreted as due to extensive partial melting. However, the seismic refraction models indicate lower-than-normal velocities and strong lateral inhomogeneities in the upper crust. Particularly obvious in the refraction data are two regions of very low seismic velocities near the Mallard Eake and Sour Creek resurgent domes in the Yellowstone caldera. The low-velocity body near the Sour Creek resurgent dome is intepreted as partially molten rock. Together with other geophysical and thermal data, the seismic results indicate that a sub-lithospheric thermal anomaly is responsible for the time-progressive volcanism along the Eastern Snake River Plain. However, the exact mechanism responsible for the volcanism and details of magma storage and migration are not yet fully understood.     

Seasonal and solar cycle variations of night-time anomalous enhancements in total electron content

Seasonal and solar cycle variations of the various characteristics of night-time anomalous enhancements in total electron content (TEC) of the ionosphere are presented for a low latitude station, Hawaii by considering TEC data for a full solar cycle. All the characteristics of the TEC enhancements have seasonal and solar cycle dependence. TEC enhancement characteristics such as frequency of occurrence, amplitude and duration are positively correlated with solar activity. The possible source mechanisms for the observed enhancements are also discussed.     

Soil,landuse and land evaluation studies of Patna area Bihar

The soil and landuse surveys have been conducted in Patna area, Bihar, using aerial photos of 1:25,000 scale. Three major systems, Ganges Gandak and interfluvial plain, have been identified in the area. These were further sub-divided into levees plains and channels etc. The soils were classified according to Soil axonomy. The major land use of the area is cultivation (62.2%) (Upland, lowland and wet land crops) plantation (1.8%) habitation (16.0%), water bodies (8.8%), barren lands (9.4%) and miscellaneous (1.8%). The soils of the area have been evaluated for different land utilization types-upland crops, lowland crops, and habitation. For paddy 75.:%, upland crops 8.2% and for habitation 57%, area was found suitable.     

The solani-ganga interfluve; an application of remote sensing technique on soil resource mapping for agricultural planning

The area of the Solani-Ganga interfluve, which lies between 29°16′N to 30°15′N latitude and 77°45′E to 78°15′E longitude was undertaken for the present study using LANDSAT imagery of band 5 and 7 and the false colour composite on the scale of 1:250,000 in combination with aerial photographs (1:25,000). Major geomorphic units, e.g., Siwalik Hills. Solani-upper alluvial plain, Solani lower alluvial plain, ‘Tarai’ and Ganga alluvial plain were delineated on LANDSAT and colour composite. Sample areas selected from LANDSAT were studied on aerial photographs in details and soil physiography relationship was developed. The soils on Siwalik hills are classified as Orthents. The soils of the pledmont plain and the recent terraces of Solani river and its tributaries were Psamments, Orthents, Fluvents, Orchrepts and Aquepts. The soils of upper alluvial tract of the Ganga plain is mostly Ustalfs with inclusion of Aqualfs, while the strong hydromorphic Tarai tract consists of partly Aquepts, Ochrepts (cultivated) and partly of Aquolls, Ustolls and Ustalfs (under forest). The present study aims to pin point the nature of soil relief relationship with the help of LANDSAT imagery and aerial photographs and diagnose the intensity of the depletion of soil resources (by prevailing factors like swift run off of biykderfed torrents, fast-flow of ground water, soil creep, mass wasting) through field studies and then treat them with ecological dose of soil conservation. For agronomic development of the region, it is worked out that the present crop-combination and crop-rotation systems should be slightly modified according to its ecosystem to prevent the depletion of soil nutrients.     

Use of remote sensing techniques for agricultural land use survey,classification and planning

A critical appraisal of the need and use of remote sensing techniques for land use mapping with particular reference to Indian conditions have been made. Land use classification system based on physiography, utility, management and identification have been suggested using remote sensing techniques at different levels of mapping.     

Multi level land use surveys using remote sensing techniques

The use of Landsat imagery at 1:1 M and 1:250,000 and aerial photos on 1:65,000 and 1:20,000 scale have been used to study landuse. It has been possible to achieve identification using Landsat imagery up to utility level ( level 1 and II ) and with the aerial photographs further subdivisions of utility into management and identification (level III and IV) .     

Petrological And Geochemical Characteristics Of The Granulitic Terrain Of Brejses, Bahia, Brazil

New petrological and geochemical characteristics of the Brejtes region, situated in the south of Bahia, Brazil are discussed. The region forms a part of the most important and extensive granulite facies terrain in Brazil of Archean/Paleoproterozoic age. Five groups of rock types all equilibrated in the granulite facies are identified in this region. They are: i) supracrustal and related rocks, ii) undifferentiated granulites, iii) hornblende bearing enderbite-charnockites, iv) hornblende free enderbite-charnockites, v) charnockites. The first group appears to be the oldest in the region as they form enclaves in the 2.9 Ga old undifferentiated granulites. The third and fourth group are enderbite-charnockites, whose protoliths constitute two series of calc-alkaline rocks, one titanium poor (hornblende free) and another titanium rich (hornblende bearing). U/Pb zircon SHRIMP dates indicate ages of formation at 2.81 Ga (hornblende free) and 2.69 Ga (hornblende bearing) for the two groups. The fifth group of rocks have charnockitic affinity and are present in the center of the Brejtes Dome. These rocks are also have calc-alkaline affinity, but show petrographic and geochemical characteristics distinct from those of other groups. Preliminary geochronological investigations by zircon Pb-Pb evaporation method yielded 2.6 Ga and 2.0 Ga for the charnockites from the inner core of the Brejtes Dome. These age data suggest that the circular structure was formed by the re-fusion of the 2.6 Ga old deep crustal material generating younger charnockites at 2.0 Ga.     

Soil survey of command area for planning of water management: A case study of an area in Hardoi district,U.P.

Development of irrigation potential for increasing agricultural production is the main aim of Command Area Development. This involves interaction amongst various factors; the soil, the crop, the climate, the topograpny and others. Water management in Command Area requires careful planning, based upon adequate data regarding soils, land use and topography. It is essential to make the best possible use of the available water without creating waterlogging, salinity and alkalinity problems in the command area. The use of aerial photographs is a well recognized expedient, convenient and economical method of data collection, which appreciably suits the requirement of the survey of Command Areas. As large areas have to be surveyed for data collection, the best way to accomplish this is by taking up survey of command area in different levels: reconnaissance, semi-detailed and detailed. The reconnaissance and semi-detailed survey would enable us to identify problem areas. Detailed survey are needed in these areas for taking up reclamation measures. A case study of soil survey carried out in the Sharda Sahayak Command Area of a part of Hardoi District is given as an example to illustrate the use of aerial photographs for planning of water management practices.     

东天山伊吾二叠纪花岗质杂岩体的锆石定年、地球化学及其构造意义

伊吾花岗质杂岩体主要由二长花岗岩和碱长花岗岩构成。锆石LA-ICP-MS U-Pb定年分析得到二长花岗岩和碱长花岗岩的侵位年龄分别为284.6±1.4Ma和284.0±1.1Ma。结合地质证据,此年龄表明该杂岩体形成于碰撞之后的二叠纪早期挤压-伸展转折阶段。岩石学、地球化学和同位素等方面的对比研究表明这两种岩石为同一岩浆演化的产物。与二长花岗岩相比,碱长花岗岩表现为硅、碱的含量较高,而铝的含量较低;富Th、U、Nb、Ta,贫Sr、P、Ti、Sm;DI和Rb/Sr升高,Nb/Ta和Zr/Hf下降,从二长花岗岩到碱长花岗岩表现出连续分异演化的趋势。计算得到二长花岗岩和碱长花岗岩的模式年龄(t_(DM))分别为693Ma和763Ma,ε_(Nd)(t)分别为+4.53和+4.64,(~(87)Sr/~(86)Sr)_i分别为0.703858和0.703855,表现出高ε_(Nd)(t)低(~(87)Sr/~(86)Sr)_i的特征。这些特征表明,伊吾岩体的岩浆来自新元古代时从亏损地幔分离出来的初生地壳源区。二长花岗岩岩浆是这种初生地壳岩浆演化的产物,而碱长花岗岩形成于二长花岗岩母岩浆经斜长石、磷灰石、钛铁氧化物、榍石、独居石、褐帘石和锆石等矿物分离结晶后的残留岩浆。