Disturbance due to a point source in a layered half-space

Summary In this paper the displacement components due to a compressional point source in a layered half-space consisting of a liquid layer of finite thickness overlying a semi-infinite solid homogeneous medium have been deduced. Two different cases have been considered. In the first case the source is taken in the liquid layer and in the second case the source is taken in the solid layer. The displacement components in cylindrical coordinates have been obtained in closed form in detail at the interface for all values of distance from the source for the second case.     

The petrology and geochemistry of intrusive alkaline rocks of Elchuru,Prakasam District,Andhra Pradesh,India

The Elchuru alkaline igneous intrusion is an arcuate-shaped ring complex, approximately 16 km² in area, cropping out in the Eastern Ghats high grade metamorphic series. It is part of an alkaline province composed of a number of intrusions which range from ijolite-melteigite to alkali gabbro (viz. malignite, melalusitanite, shonkinite) and then to hypersolvus nepheline syenite followed by subsolvus nepheline syenite. The complex is cut by late lamprophyric dykes. A nephelinized alkaline gneiss, within the investigated complex, is the only deformed rock type and is regarded as an older unit not related to the comagmatic series. The remainder of the complex was emplaced post-tectonically. Sovitic carbonatite is a conspicuous Iithologic unit associated with the complex. Chemical analyses of 19 selected samples for 13 major oxides and 5 trace elements (Rb, Ba, Sr, Zr and Nb) are presented to establish a geochemical model for the investigated complex. The mineralogy, petrography and geochemistry of the rocks of the Elchuru Alkaline Complex suggest that it was formed by differentiation of an initially alkali-rich ijolitic magma as reflected in the crystallization of nepheline, kaersutitic amphibole and alkali feldspar. With progressive increase in alkali feldspar content (volume percentage) the ijolite passes to malignite and then nepheline syenites. Amphibole shows sodic enrichment from a dominant calcic variety. Pyroxene, likewise, shows sodic enrichment following the scheme salite-ferrosalite to aegirine-augite. The igneous cycle closes with the intrusion of biotite lamprophyre. There is a systematic increase in total alkalies (Na₂O+K₂O) and decrease in CaO from the early mafic rocks to the syenitic rocks. The alkali-lime index of the complex is 48 indicating its strongly alkaline nature (Peacock 1931), and they are miaskitic in character (agpaicity index <1, Currie 1976). Such miaskitic complexes are associated with carbonatites (Heinrich 1966).     

Alkaline rocks of Samchampi-Samteran, District Karbi-Anglong, Assam, India

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.     

Sedimentary characteristics of palaeolake deposits along the Indus River valley,Ladakh, Trans‐Himalaya: Implications for the depositional environment

This study is an attempt to contribute to the data set of granulometric studies of sediments by measuring the sedimentary structure and texture, along with statistical parameters, of cold and arid lake systems. The palaeolake sequence along the River Indus on the western fringe of the Tibetan Plateau in Ladakh sector was selected in order to shed light on depositional environmental changes within the lake from post‐last glacial maximum to 5 ka. The River Indus was blocked by Lamayuru dam burst during the deglaciation, after the Last Glacial Maximum (LGM) and the subsequent increase in water level led to the formation of the Saspol–Khalsi palaeolake. This lake was ca 55 km in length, extending from Nimo to Khalsi, had a surface area of 370 km² and was in existence until 5 ka. Two sections (Saspol and Khalsi) separated by an aerial distance of 35 km show a similar trend in sediment character due to their deposition in the same lake system. Grain‐size studies show a polymodal nature of sediments for both of the sections. However, sediments of the lower/downstream section (Khalsi) show a poorer degree of sorting, and coarser grain size and high energy depositional condition as compared with the sediments of Saspol section (positioned upstream) due to the location of the sections within the lake system. It was noted that, in high‐altitude arid regions, the sedimentological characteristics of large‐sized valley lakes may vary greatly, horizontally as well as vertically, owing to local stream input, inflow intensity from the catchment, outflow velocity of water channels, lithology and valley widths at the different sites.     

Experimental study of the joins forsterite–diopside–leucite– and forsterite–leucite–åkermanite up to 2.3 GPa [P(H2O) = P(Total)] and variable temperatures: Its petrological significance

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 forsterite_ss + diopside_ss + leucite_ss + 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 forsterite_ss, phlogopite_ss, kalsilitess, K-feldspar_ss and diopside_ss. It has the following three five-phase points: 1) one occurring at Fo₉Di₄₉Lc₄₂ and 1005 ± 5 °C, where liquid and vapour coexists with forsterite_ss, phlogopite_ss and diopside_ss (phlogopite-bearing madupite), 2) the second one at Fo₄Di₅₀Lc₄₆ and 990 ± 10 °C, where diopside_ss, K-feldspar_ss and phlogopite_ss coexist with liquid and vapour (pyroxene-bearing minette), and 3) the third one at Fo₃Di₂₁Lc₇₆ and 775 ± 5 °C, where phlogopite_ss, kalsilite_ss and K-feldspar_ss 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 forsterite_ss, phlogopite_ss, kalsilite, K-feldspar_ss, diopside_ss and merwinite_ss. The data indicate the presence of four five-phase points: 1) one occurring at Fo₇Lc₄₂Ak₅₁ and 1165 ± 5 °C, where phlogopite_ss, forsterite_ss, diopside_ss 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 phlogopite_ss, K-feldspar_ss, diopside_ss and vapour (pyroxene-bearing minette), 3) the third one at Fo₁₈Lc₂₁Ak₆₁ and 1255 ± 10 °C, where merwinite_ss, forsterite_ss and diopside_ss are in equilibrium with liquid and vapour (merwinite-bearing wherlite), and 4) the fourth one at Fo₅Lc_73.5Ak_21.5 and 770 ± 5 °C, where kalsilite_ss, phlogopite_ss 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.     

The role of women in internal migration in Zambia

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.     

Mafic alkalic magmatism in central Kachchh,India: a monogenetic volcanic field in the northwestern Deccan Traps

Magmatism in Kachchh, in the northwestern Deccan continental flood basalt province, is represented not only by typical tholeiitic flows and dikes, but also plug-like bodies, in Mesozoic sandstone, of alkali basalt, basanite, melanephelinite and nephelinite, containing mantle nodules. They form the base of the local Deccan stratigraphy and their volcanological context was poorly understood. Based on new and published field, petrographic and geochemical data, we identify this suite as an eroded monogenetic volcanic field. The plugs are shallow-level intrusions (necks, sills, dikes, sheets, laccoliths); one of them is known to have fed a lava flow. We have found local peperites reflecting mingling between magmas and soft sediment, and the remains of a pyroclastic vent composed of non-bedded lapilli tuff breccia, injected by mafic alkalic dikes. The lapilli tuff matrix contains basaltic fragments, glass shards, and detrital quartz and microcline, with secondary zeolites, and there are abundant lithic blocks of mafic alkalic rocks. We interpret this deposit as a maar-diatreme, formed due to phreatomagmatic explosions and associated wall rock fragmentation and collapse. This is one of few known hydrovolcanic vents in the Deccan Traps. The central Kachchh monogenetic volcanic field has >30 individual structures exposed over an area of ∼1,800 km² and possibly many more if compositionally identical igneous intrusions in northern Kachchh are proven by future dating work to be contemporaneous. The central Kachchh monogenetic volcanic field implies low-degree mantle melting and limited, periodic magma supply. Regional directed extension was absent or at best insignificant during its formation, in contrast to the contemporaneous significant directed extension and vigorous mantle melting under the main area of the Deccan flood basalts. The central Kachchh field demonstrates regional-scale volcanological, compositional, and tectonic variability within flood basalt provinces, and adds the Deccan Traps to the list of such provinces containing monogenetic- and/or hydrovolcanism, namely the Karoo-Ferrar and Emeishan flood basalts, and plateau basalts in Saudi Arabia, Libya, and Patagonia.     

Quantification of irreversible benzene sorption in sandy materials

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.     

Albedo enhancement over land to counteract global warming: impacts on hydrological cycle

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.