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11.
The Samchampi-Samteran alkaline igneous complex (SAC) is a near circular, plug-like body approximately 12 km2 area and is emplaced into the Precambrian gneissic terrain of the Karbi Anglong district of Assam. The host rocks, which
are exposed in immediate vicinity of the intrusion, comprise granite gneiss, migmatite, granodiorite, amphibolite, pegmatite
and quartz veins.
The SAC is composed of a wide variety of lithologies identified as syenitic fenite, magnetite ± perovskite ± apatite rock,
alkali pyroxenite, ijolite-melteigite, carbonatite, nepheline syenite with leucocratic and mesocratic variants, phonolite,
volcanic tuff, phosphatic rock and chert breccia.
The magnetite ± perovskite ± apatite rock was generated as a cumulus phase owing to the partitioning of Ti, Fe at a shallow
level magma chamber (not evolved DI = O1). The highly alkaline hydrous fluid activity indicated by the presence of strongly
alkalic minerals in carbonatites and associated alkaline rocks suggests that the composition of original melt was more alkalic
than those now found and represent a silica undersaturated ultramafic rock of carbonated olivine-poor nephelinite which splits
with falling temperature into two immiscible fractions—one ultimately crystallises as alkali pyroxenite/ijolite and the other
as carbonatite. The spatial distribution of varied lithotypes of SAC and their genetic relationships suggests that the silicate
and carbonate melts, produced through liquid immiscibility, during ascent generated into an array of lithotypes and also reaction
with the country rocks by alkali emanations produced fenitic aureoles (nephelinisation process). Isotopic studies (δ18O and δ13C) on carbonatites of Samchampi have indicated that the δ13C of the source magma is related to contamination from recycled carbon. 相似文献
12.
Nag P 《Population geography : a journal of the Association of Population Geographers of India》1983,5(1-2):60-69
Zambia's urban population increased from 29% to 43% between 1969-80. Female migration, although modest, played an important role in improving the sex ratio in urban areas. In 1980, there were 962 males/1000 females in Zambia as a whole and 1061/1000 in the urban areas. This compares with 960 males/1000 females in Zambia as a whole in 1969 and 1113/1000 in the urban areas. This overall decrease in the number of males/1000 females in urban areas has had implications for Zambian household structure and for the matrilineal social structure. The single male household traditional to urban areas can be expected to be increasingly replaced by complete households of larger size. Family size has tended to be smaller in provinces that have been affected by outmigration. The historically different propensities of males and females to participate in internal migration has meant that the actual number of family units has been smaller than the potential number. However, this pattern can be expected to normalize as female migration continues to increase. In rural areas, this trend should lead to a decline in the number of female household heads and implications for matrilineal land ownership patterns and agricultural output. 相似文献
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Based on a previous study of the irreversible sorption of benzene in sandy aquifer materials, we further investigated a method to quantify an irreversible sorption coefficient of aqueous benzene. Assuming that the rate of irreversible loss from the solution to the sorption sites followed first‐order kinetics, the irreversible sorption coefficient was derived from a kinetic batch sorption test conducted for an appropriate soil‐to‐solution ratio to reflect the flow conditions imposed on a column test. Simulation results revealed that the irreversible sorption coefficient estimated from the kinetic batch test provided a good agreement with the measured data obtained from the column test, indicating that the method proposed in this study can be used to quantify the irreversible sorption coefficient. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
15.
A recent modelling study has shown that precipitation and runoff over land would increase when the reflectivity of marine clouds is increased to counter global warming. This implies that large scale albedo enhancement over land could lead to a decrease in runoff over land. In this study, we perform simulations using NCAR CAM3.1 that have implications for Solar Radiation Management geoengineering schemes that increase the albedo over land. We find that an increase in reflectivity over land that mitigates the global mean warming from a doubling of CO2 leads to a large residual warming in the southern hemisphere and cooling in the northern hemisphere since most of the land is located in northern hemisphere. Precipitation and runoff over land decrease by 13.4 and 22.3%, respectively, because of a large residual sinking motion over land triggered by albedo enhancement over land. Soil water content also declines when albedo over land is enhanced. The simulated magnitude of hydrological changes over land are much larger when compared to changes over oceans in the recent marine cloud albedo enhancement study since the radiative forcing over land needed (?8.2?W?m?2) to counter global mean radiative forcing from a doubling of CO2 (3.3?W?m?2) is approximately twice the forcing needed over the oceans (?4.2?W?m?2). Our results imply that albedo enhancement over oceans produce climates closer to the unperturbed climate state than do albedo changes on land when the consequences on land hydrology are considered. Our study also has important implications for any intentional or unintentional large scale changes in land surface albedo such as deforestation/afforestation/reforestation, air pollution, and desert and urban albedo modification. 相似文献
16.
We conducted a series of melting experiments in the join forsterite–diopside–leucite under 0.1 and 2.3 GPa and in the join forsterite–leucite–åkermanite under 2.3 GPa to understand paragenetic relationships amongst different types of lamproitic and lamprophyric magmas with K-rich mafic and ultramafic volcanic (kamafugitic) rocks. Both the joins were studied in the presence of excess water. The experimental results of the join forsterite–diopside–leucite at 0.1 GPa show that the five-phase point of forsterite (Fo)ss + diopside (Di)ss + leucite (Lc)ss + liquid (Liq) + vapour (V) (equivalent to ugandite lava) occurs at Fo2Di50Lc48 at 880 ± 5 °C. Phlogopite appears as the last phase at 830 ± 15 °C. The final crystalline assemblage of forsteritess + diopsidess + leucitess + phlogopite is similar to the phenocryst assemblage of missourite lava. Present study suggests that an olivine leucitite (ugandite) can be derived from an olivine italite, a slightly potassic peridotite and a leucitite magma.
A study of the join Fo–Di–Lc [P(H2O) = P(Total)] at 2.3 GPa shows that liquid compositions penetrate the primary phase volumes of forsteritess, phlogopitess, kalsilitess, K-feldsparss and diopsidess. It has the following three five-phase points: 1) one occurring at Fo9Di49Lc42 and 1005 ± 5 °C, where liquid and vapour coexists with forsteritess, phlogopitess and diopsidess (phlogopite-bearing madupite), 2) the second one at Fo4Di50Lc46 and 990 ± 10 °C, where diopsidess, K-feldsparss and phlogopitess coexist with liquid and vapour (pyroxene-bearing minette), and 3) the third one at Fo3Di21Lc76 and 775 ± 5 °C, where phlogopitess, kalsilitess and K-feldsparss are in equilibrium with liquid plus vapour (kalsilite-bearing minette).
The experimental results of the join Fo–Lc–åkermanite (Ak) show that the join 40 penetrates the primary phase volumes of forsteritess, phlogopitess, kalsilite, K-feldsparss, diopsidess and merwinitess. The data indicate the presence of four five-phase points: 1) one occurring at Fo7Lc42Ak51 and 1165 ± 5 °C, where phlogopitess, forsteritess, diopsidess coexists with liquid and vapour (olivine-bearing madupite), 2) the second one at Fo3Lc49Ak48 and 1140 ± 10 °C, where a liquid is in equilibrium with phlogopitess, K-feldsparss, diopsidess and vapour (pyroxene-bearing minette), 3) the third one at Fo18Lc21Ak61 and 1255 ± 10 °C, where merwinitess, forsteritess and diopsidess are in equilibrium with liquid and vapour (merwinite-bearing wherlite), and 4) the fourth one at Fo5Lc73.5Ak21.5 and 770 ± 5 °C, where kalsilitess, phlogopitess and K-feldspar coexist with liquid and vapour (kalsilite-bearing minette). The present data suggest that high pressure heteromorphic equivalent of a katungite magma is represented by a kalsilite-bearing minette, a pyroxene-bearing minette, or an olivine-bearing madupite. 相似文献
17.
P.R. Sen Gupta Kashi Ram A.K. Das S.R. Paul B.K. Guha D.K. Nag 《Meteoritics & planetary science》1985,20(3):583-589
The Gujargaon meteorite was observed to fall on a cotton field at Gujargaon in Dewas district, Madhya Pradesh, India, on the afternoon of the 4th of September, 1982. It is an oriented stone with a saucer-shaped front and regmaglypted rear with surfaces of more than one generation, and is entirely covered by fusion crust. Gujargaon is an H5 chondrite with rare chondrules integrated with the matrix. Intense fracturing with fractures filled by glassy veins, and undulose extinction and deformation-twin lamellae in troilite bear evidences of shock. Compared to average H-group chondrites Gujargaon appears to have higher contents of SiO2and normative pyroxene. 相似文献
18.
K. R. Nag 《Pure and Applied Geophysics》1962,52(1):115-126
Summary In this paper, the displacements produced at the surface of a semi-infinite, clastic medium by the sudden creation and subsequent motion of discontinuities in the normal and tangential stresses have been obtained in the form of definite integrals byCagniard's method. Numerical values are given in a particular case.Published with the kind permission of the Director General, Geological Survey of India, Calcutta. 相似文献
19.
The data of proton fluences measured in three ranges of energy values (1 MeV, 10MeV, and 100 MeV) in the current solar cycle 22 have been analysed to detect periodicities. Power spectral analysis of the time series of the data of proton fluences shows a periodicity of 74 days, which conforms to that of other kinds of solar activity as reported by earlier authors, thus indicating the intimate relationship of proton emission with solar activity. 相似文献
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