Historical geomorphology and pedology of the Gandak Megafan,Middle Gangetic Plains,India

The Gandak megafan of eastern Uttar Pradesh and northwestern Bihar lies in the Middle Gangetic Plains. The Gandak River has shifted about 80 km to the east due to tilting in the last 5000 years. This has created a soil chronoassociation similar to the chronosequences found on some flights of river terraces. This chronoassociation has five members, QGD1-5. They are distinguished on the basis of profile development, clay mineralogy and calcium carbonate content. Chlorite transforms to vermiculite on a large scale from QGD1 to QGD3 and decreases drastically in member QGD4. Kaolinite and interstratified kaolinite-smectite are abundant in the older members of the chronoassociation. The youngest soils (QGD1:? < 500 b.p.) are found on the floodplains of the major rivers. QGD2 soils, like those of the Young Gandak Plain, date from? > 500 b.p., while QGD3 soils, like those on the Older Gandak Plain and Old Rapti Plains date back to 2500 b.p. QGD4 soils, like those on the Oldest Gandak Plain, are dated as? 5000 years b.p., whilst the oldest QGD5 soils, as on the Old Ghaghra Plain and Ganga-Ghaghra Interfluve, date back to 10000 b.p. These soils, which include pedogenic calcite and a? saline epipedon, indicate a dry climatic spell during the period 9000-11000 b.p. Faults developed on the megafan are not related to the basement structures.     

Boundary shock waves in a conducting gas

Summary In this paper, we have postulated, in a conducting gas, the occurrence of a boundary shock wave, considered as a quick transition region in which the viscous effects are compressive and are confined to a thin layer adjacent to a surface. The analogues of the well known Rankine-Hugoniot jump relations, Prandtl relation, and other properties of a shock wave are derived and a discussion about the existence of a boundary shock wave is made.     

Petrochemistry of the deccan trap flows of linga,Chhindwara district,M.P., India

Five representative cumulative samples of basal flows were chemically analysed. Normative composition (CIPW),DI, FI, MI, SI, f (norms) and ‘S’ indices have been calculated therefrom. It is concluded that the Linga flows are tholeiitic in nature with slightly more FeO, MgO and Al₂O₃ than most tholeiitic basalts. They represent eariy-middle stage basalts with DI less than 30. Thef-norms put these flows in the pyroxene field indicating an early fractionation of pyroxenes causing relative iron enrichment. Textural evidences, also, support a late fractionation of feldspar with overlapping periods of crystallisation of pyroxene and feldspar. The similarity in composition of the lower flows is more apparent than true. The trend of differentiation is characteristically tholeiitic. Oxygen and vapour fugacity may have been responsible for a shift in the general trend of differentiation. Explosive eruption of the magma, which was well mixed and which cooled rapidly, is borne by the features exhibited by these flows.     

On the vibrations of a composite orthotropic cylinder placed in a magnetic field

Summary The problems of radial vibration of a composite orthotropic cylinder subjected to a uniform axial magnetic field forms the chief interest of the paper.     

Crustal structure of the Indian subcontinent

Studies carried out by various investigators up to 1971 to delineate the Indian crustal structure using body wave travel times, surface wave dispersion and gravity methods are summarised and reviewed. The average crustal thickness is found to be 35–40 km in the Indian peninsular shield, 30–35 km in the Indo Gangetic plains and 60–80 km in the Himalayas and the Tibetan plateau region. The limitations of the various methods used and the errors in the estimation of crustal thickness by them are discussed. As no deep refraction work for crustal studies has been carried out so far in India, this topic is not covered in this study.     

Mapping runoff generating areas using AGNPS-VSA model

ABSTRACT

In humid regions, surface runoff is often generated by saturation-excess runoff mechanisms from relatively small variable source areas (VSAs). However, the majority of the current hydrologic models are based on infiltration-excess mechanisms. In this study, the AGricultural Non-Point Source Pollution (AGNPS) model was used to integrate the VSA concept using topographic wetness index (TWI). Both the original and AGNPS-VSA models were evaluated for a small agricultural field in Ontario, Canada. The results indicate that the AGNPS-VSA model performed better than original model. The AGNPS-VSA model predicted that only the saturated portion of the field with higher TWI values produced runoff, whereas the original AGNPS model showed uniform hydrologic response from the entire field. The results of this study are important for accurately mapping the locations of VSAs. This new model could be a powerful tool in identifying critical source areas for applying targeted best management practices to minimize pollutant loads to receiving waters.     

Observational Study of the Three-Dimensional Magnetic Field Structure and Mass Motion in Active Regions

Spectro-polarimetric observations of active regions were carried out in the spectral lines of Sii 10827.1 Å and Hei 10830 Å to study the three-dimensional magnetic field structure and associated plasma flow properties. Comparison of Sii and Hei magnetograms with the potential field model shows that a large fraction of the magnetic field is consistent with the potential field structure, by assuming that the height difference between the origin of the two lines is about 1200 km. The slope of the scatter plot between Sii and Hei magnetograms is 0.5, 0.76 in an emerging flux and a larger active region, respectively. These values are lower than the scatter plot slopes obtained from Kitt Peak photospheric and chromospheric magnetograms, in which case the corresponding values are 0.83 and 0.9, respectively. Considering the height difference between these two sets of chromospheric magnetograms, this implies that the magnetic field spreads out faster near the transition region heights. Dopplergrams obtained by determining the centroid of the asymmetric line profiles show that, in case of emerging flux region, the chromospheric upflow regions are located in the magnetic neutral line areas.     

Geo-engineering properties of expansive soil treated with xanthan gum biopolymer

ABSTRACT

This paper presents the effectiveness of xanthan gum (XG) biopolymer in stabilising the expansive soil. The XG biopolymer is mixed with expansive soil in different proportions such as 0%, 0.2%, 0.5%, 0.8% and 1.0% by weight of the dry soil mass. The plasticity, compaction, swelling, compressibility, hydraulic conductivity, strength and durability characteristics of the treated and un-treated expansive soil are examined. Results show that the plasticity index of the treated soil mass initially increases but beyond 0.5% biopolymer addition it decreases sharply. The optimum moisture content and maximum dry density of treated soil, found out from light and heavy compaction tests, do not follow any definite trend. It is also found that increasing XG content increases compressibility slightly but, it reduces swelling pressure, differential free swelling value and hydraulic conductivity remarkably. On the other hand, time-dependent compressive strength and resistance to mass loss increases with increasing XG content. Microscopic examination confirms the formation of gel-like linkage, which brings about the modifications in the treated expansive soil.     

Emerging Flux and X-class Flares in NOAA 6555

The active region NOAA 6555 had several locations of highly sheared magnetic field structure, yet, only one of them was the site for all the five X-class flares during its disk passage in March 1991. The pre-flare observations of high-resolution H filtergrams, vector magnetograms and H Dopplergrams of the 2B/X5.3 flare on 25 March 1991 show that the flaring site was characterized by a new rising emerging flux region (EFR) near the highly sheared magnetic field configuration. The polarity axis of the emerging flux was nearly perpendicular to the pre-existing magnetic neutral line. The location of the EFR was the site of initial brightening in H. The post-flare magnetograms show higher magnetic shear at the flare location compared to the post-flare magnetograms, which might indicate that the EFR was sheared at the time of its emergence. As the new EFR coincided with the occurrence of the flare, we suggest that it might have triggered the observed flare. Observations from Big Bear Solar Observatory and Marshall Space Flight Center also show that there was emergence of new flux at the same location prior to two other X-class flares. We find that out of five observed X-class flares in NOAA 6555, at least in three cases there are clear signatures of flare-related flux emergence. Therefore, it is concluded that EFRs might play an important role in destabilizing the observed sheared magnetic structures leading to large X-class flares of NOAA 6555.     

Mildly alkaline basalts from Pavagadh Hill, India: Deccan flood basalts with an asthenospheric origin

Summary Of twelve flows at Pavagadh Hill, the two three-phenocryst-basalt flows with Mg#0.70 and Ni/MgO33 are the most primitive and perhaps as primitive as any basalts in the Deccan province. Scatter on variation diagrams and the occurrence of primitive flows at two different levels in the volcanic sequence implies that most rocks are probably not, strictly speaking, comagmatic. Nevertheless, mass balance calculations indicate a generalized differentiation scheme from primitive basalt to hawaiite that involved removal of olivine, augite, plagioclase and Fe-Ti oxides in the proportions 40:33:22:5 with 50% of the magma remaining. Crustal assimilation had a minimal effect on evolution of the basalts but rhyolites at the top of the volcanic sequence may have been produced by crustal melting following prolonged heat release from alkali basalt pooled along fault zones in the continental crust. Major element based calculations indicate that the most primitive basalts were generated by 7 to 10% melting of mantle peridotite. These low percentages of melting, typical of alkali basalts, are consistent with the steep slopes on chondrite-normalized REE diagrams. Low heavy REE concentrations point to residual garnet in the source region. Incompatible element concentrations (e.g. Rb, Ba, Zr, La) in Pavagadh basalts exceed those in Deccan tholeiitic basalts but are substantially lower than those reported for some other Deccan alkali basalts. Obviously Pavagadh basalts do not reflect the lowest percentages of melting and greatest amount of source region metasomatic enrichment attained in the Deccan province. Deccan tholeiitic and alkali basalts are largely characterized by low La/Nb ratios and high La/Ba ratios similar to those in oceanic island basalts. This indicates minimal involvement of the subcontinental lithospheric mantle in their petrogenesis. Comparison with continental mafic magma provinces where a subcontinental lithospheric mantle imprint is common indicates long periods of extension and/or melting of mantle lithosphere still hot from pre-extension subduction are more likely to produce magmas bearing the lithospheric imprint.

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Alkalische Basalte von Pavagadh Hill, Indien: Deccan-Flutbasalte von Astenosphärischer Herkunft

Zusammenfassung Im Gebiet von Pavagadh Hill, Indien, treten 12 Spät-Deccan und rhyolithische alkalibasaltische Ergüsse und Intrusiva auf. Variationsdiagramme zeigen, daß die Abfolge nicht komagmatisch ist. Zusammen mit Berechnungen der Massenbilanz unterstützen sie vielmehr ein Zwei-Stadienmodell für die Entstehung von Hawaiiten aus sehr primitiven (i.e. Mg#=Mg/(Mg+.(0.9*Fe_totat)) at.%0.70) Basalten. Olivin und Augit dominierten die frühe Fraktionierung während Augit vorherrschte als der Magmaanteil von 65% auf 50% sank. Die Entfernung von Plagioklas spielte bei der Differentiation nur eine geringe Rolle. Niedrige Th/Nb (0,2), Rb/Sr(<0,12) und K/NbVerhältnisse geben keine Hinweise auf signifikante Assimilation von Krustenmaterial. Die Seltene-Erd-Verteilungsmuster (SEE), niedrige Gehalte an schweren SEE sowie die Hauptelementspektren der Alkalibasalte weisen auf eine granatführende Ursprungsregion und auf einen Aufschmelzungsgrad von nur 7% bis 10% hin. Es gibt jedoch auch stärker alkalische (höhere Rb, Zr etc.) Deccanbasalte (i.e. Rajpipla). Die Assoziation von Deccanalkalibasalten, Rhyolithen und Störungszonen zeigt, daß letztere die Extraktion von Magma aus dem Mantel erleichterten und dazu führten, daß Magma aus Magmenkammern Krustenschmelzen (Rhyolithe) produzierte. Deccanbasalte tendieren zu hohen La/Ba und niedrigen La/Nb-Verhältnissen; dies weist auf eine asthenosphärische Herkunft hin, selbst wenn die Gesteine verhältnismäßig spät gebildet wurden (i.e. Pavagadh). Längere Perioden von Krustenextension oder von Subduktion, die der Extension vorhergeht, führt offensichtlich zur Entstehung von Magmen mit einer lithosphärischen Komponente.