A new occurrence of sapphirine-spinel-corundum-bearing granulite from NE of Jagtiyal, Eastern Dharwar Craton, Andhra Pradesh

We report a new occurrence of sapphirine-spinel-corundum bearing granulites enclosed in granitic gneisses near Jagtiyal in the Eastern Dharwar Craton (EDC). These granulites are very important in deciphering the prehistory of the thermal peak of metamorphism due to the presence of refractory phases. The appearance of sapphirine is related to the following reactions: (a) Spl₁ + Crd₁ = Spr_{1 (2:2:1)} (b) Phl (in Bt₁) + Crn₁ = East (in Bt₂) + Spr_{2 (7:9:3)} + Crd₂ (c) Bt₂ + Crd₁ + Crn₁ = Spr_{2 (7:9:3)} + Kfs + H₂O (d) Crd₁ + Spl₁ + Crn₁ = Spr_{2 (7:9:3)}. The P-T evolution of these sapphirine granulites has been constrained through the use of THERMOCALC program. Temperature of formation of sapphirine-spinel assemblages is high, around 800 °C, and pressure ranges from 5–7 kbars, suggesting that sapphirine formation took place during decompression stage.     

Sphene coronites from Hyderabad granites,Andhra Pradesh,India

Sphene coronites around magnetite are recorded in the granodiorite of Hyderabad. The metamorphic origin of the corona is discussed.     

Petrology of calc-silicate rocks from Koduru,Andhra Pradesh,India

Mineral assemblages, rock and mineral chemistry, and mineral reactions, in calc-silicate rocks from Koduru area, Andhra Pradesh, India are discussed. Mineralogical and bulk chemical differences indicate 3 calc-silicate rock types — type I with K feldspar+calcite+wollastonite+quartz+scapolite+diopside_ss +andradite_ss+sphene, has relatively high rock oxidation ratios. Type II is a highly calcic variety with high rock MgFe ratios, and has K feldspar+calcite+wollastonite+quartz+scapolite + diopside_ss±grossularite_ss+sphene+zoisite. Type III has K feldspar +calcite+wollastonite+quartz+scapolite+diopside_ss +sphene+hornblende+magnetite, and has relatively low oxidation ratio and low MgFe ratio. The 3 calc-silicate rock types have originated as mixtures of limestone/dolomite/marl.Diopside was produced by a reaction involving Ca-amphibole +calcite+quartz, and reversed during retrogression. Andradite_ss in type I rocks was produced at the expense of hedenbergitic component of pyroxene in a continuous reaction as a consequence of increase in the oxygen content of the original sediment relative to type III. Calcite+quartz reacted to give wollastonite. During cooling an influx of water caused scapolite to alter to zoisite.     

Geoenvironmental effects of groundwater regime in Andhra Pradesh, India

 The Indian subcontinent has the largest semi-arid tropical (SAT) area among developing nations. The State of Andhra Pradesh falls under the SAT region in India and is mostly covered by compact and hard rocks, characterized by seasonal rainfall of a highly fluctuating nature, in both space and time. As a consequence of the green revolution and an increase in industrial activity, there has been an increase in the utilization of groundwater resources during the last two decades in Andhra Pradesh. The development has also caused a number of problems, such as water table decline, decrease in well yields and seawater intrusion. Although major irrigation projects have contributed to improved agricultural production, the associated problems of waterlogging, salinization and loss of valuable bioresources have led to the gradual degradation of the land, affecting agricultural productivity. Surface water and groundwater have also been polluted in several parts of the State because of untreated discharge of effluents from the industries into nearby streams or open lands. A brief account of the overall scenario of the hydrogeological framework and geo-environmental effects on the groundwater regime in Andhra Pradesh is presented. Possible management practices and conservation methods are suggested. Received: 9 August 1999 · Accepted: 10 July 2000     

The Purimetla gabbros,Prakasam District,Andhra Pradesh,India

Gabbros at Purimetla occur in close association with the alkaline pluton. Petrography and petrochemistry of these gabbros indicate their tholeiitic nature. Chemical variation of these tholeiites suggests that an initial undersaturated tholeiitic magma yielded oversaturated fractions in the final stages of differentiation. Their regional distribution suggests that basic magmatism preceded the emplacement of the alkaline rocks in the Prakasam alkaline province.     

Geochemistry of Archean Metavolcanic Rocks from Kadiri Schist Belt, Andhra Pradesh, India

The basic volcanic group exposed in the Kadiri schist belt includes high Mg-basalt, basalt, basaltic andestite and dacite. The basalts are tholeiitic in composition and high Mg-basalts, basaltic andesites and dacites show calc-alkaline affinity. Major and trace element characteristics suggest that the volcanic suite has been derived from an initial tholeiitic magma which has given rise to an early basaltic type and a later calc-alkaline type of rocks. An island arc and active continental margin tectonic setting was inferred for these rocks.     

The impact of paleo-channel on groundwater contamination,Andhra Pradesh,India

 Nakka vagu, a tributary of the River Manjira in the Medak district of Andhra Pradesh, has a catchment area of ∼500 km². Patancheru is an industrial development area (IDA) near the vagu. There are about 350 industries of varied nature (pulp, plastic, bulk drugs, pharmaceuticals, paints and steel rolling mills) that are engaged in the manufacture/processing of their respective products and that use water extensively. The hydrogeological setup has a bearing on the widespread contamination in the area because of discharge of industrial effluents into open land and streams. Several dug wells and boreholes situated in the study area have been monitored for water level fluctuations and quality variations. Pumping tests have been conducted to evaluate aquifer parameters. The geology, drainage, chemistry and other related anthropogenic factors play a major role in the spread of pollution in the area. Hence, it is very important to determine the degree of vulnerability to pollution based on hydrogeological factors. Amidst the granite terrain, the Nakka vagu has been identified as a paleo-channel (composed of clay–silt–sand facies); its presence in the area has immensely increased the spread of groundwater contamination. The transmissivity of the alluvial aquifer varies from 750 to 1315 m²/day. The adjoining granite has a transmissivity that varies from 30–430 m²/day. The thickness of the valley fill in the discharge region is about 10–12 m, with a lateral spread of 500–700 m, east of Nakka vagu. Received: 17 November 1999 · Accepted: 14 March 2000     

Tectonic Setting of the Kadiri Schist Belt, Andhra Pradesh, India

Plate tectonic activity has played a critical role in the development of petrotectonic associations in the Kadiri schist belt. The calc alkaline association of basalt, andesite, dacite and rhyolite(BADR) is the signature volcanic rock suite of the convergent margin. The N-S belt has gone below the unconformity plane of Cuddapah sediments. In the northern part geochemical and structural attributes of the Kadiri greenstone belt is studied along with microscopic observations of selected samples. Harker diagram plots of major elements generally indicate a liquid line of descent from a common source, such that BADR rocks are derived from a common parent magma of basaltic to andesitic composition. These calc-alkaline volcanic rocks are formed at convergent margins where more silicic rocks represent more highly fractionated melt. All the litho-units of this greenstone belt indicate crush and strain effects. The stretched pebbles in the deformed volcanic matrix with tectonite development along with associated greenschist facies metamorphism, alteration and hydration is remarkable. Flow foliation plane with N-S strike and very low angle(5° to 10°) easterly dip and N-S axial planar schistosity formed due to later phase isoclinal folding can be clearly identified in the field. Basic intrusives are quite common in the surrounding area. All the observations including the field setting and geochemistry clearly demonstrate ocean-continent subduction as the tectonic environment of the study area.     

Fluorine distribution in waters of Nalgonda District, Andhra Pradesh, India

Geochemical and hydrochemical studies were conducted in Nalgonda District (A.P.), to explore the causes of high fluorine in waters, causing a widespread incidence of fluorosis in the local population. Samples of granitic rocks, soils, stream sediments, and waters were analyzed for F and other salient chemical parameters. Samples from the area of Hyderabad city were analyzed for comparison. The F content of waters in areas with endemic fluorosis ranges from 0.4 to 20 mg/l. The low calcium content of rocks and soils, and the presence of high levels of sodium bicarbonate in soils and waters are important factors favoring high levels of F in waters.     

A biogeochemical study of the Podili and Tirupati area of Andhra Pradesh, India

 The fluoride content of dung, urine and milk of grazing animals, for example cow, she-buffalo, doe and ewe, was studied in the Podili area, India, (endemic fluorosis) and also in Tirupati (non-fluorosis) for the purpose of comparison. The data reveal that the fluoride content of the urine of animals is suitable for the preparation of biogeochemical atlases studying the environmental effect in relation to health. Received: 1 August 1997 · Accepted: 2 March 1998     

Alkaline basic intrusives of Elchuru,Prakasam District,Andhra Pradesh,India

The igneous alkaline rocks at Elchuru start from a parent ijolite-melteigite association to basic malignite, melalusitanite and shonkinite followed by nepheline syenites and then biotite lamprophyres (as dykes) at the waning phase of the evolutionary course of the complex. The distinct alkalinity of the rocks is manifested by the development of modal nepheline and calcic amphibole (kaersutite). For both the basic rocks,i.e. alkali gabbro and biotite lamprophyre, the percentages of normative nepheline are always higher than modal nepheline, indicating silica deficiency and alkali enrichment of the mafics. It is evident from detailed petrological and geochemical studies that the two basic members are very much akin to each other and there is no major deviation in their bulk chemistry.     

Fluoride-bearing groundwater in Gummanampadu Sub-basin, Guntur District, Andhra Pradesh, India

The functional factors responsible for fluoride (F^?)-bearing groundwater used for drinking as well as for cooking in the area of Gummanampadu Sub-basin, Guntur District, Andhra Pradesh, India are discussed. The study area is a part of an Archean Gneissic Complex, consisting of banded-biotite-hornblende-gneisses, over which the Proterozoic Cumbhum quartzites, shales, phyllites, and dolomitic limestones occur. The chemistry of groundwater is dominated by carbonates (HCO₃ ^? and CO₃ ^2?) at a higher pH. This results in a higher total alkalinity over total hardness, causing an excess alkalinity. Sodium ion is dominated among the cations (Ca²⁺, Mg²⁺, and K⁺). The concentration of F^? (2.1–3.7 mg/L) is higher than that of desirable national limit (1.2 mg/L) prescribed for drinking purpose. A significant positive correlation exists between F^? and pH as well as that between F^? and HCO₃ ^? + CO₃ ^2?. This indicates that the alkaline condition is the prime conducive factor for dissolving F^?-bearing minerals more effectively leading to a higher concentration of F^? in the groundwater. Furthermore, a positive chloro-alkaline index reflects the ion exchange, and an oversaturation with respect to CaCO₃ indicates the evaporation. In addition, a negative relation between the well depth and F^? shows the effect of solubility and/or leaching of salts in different depth levels. These factors regulate the concentration of F^? in the groundwater. On the other hand, a positive correlation of F^? with SO₄ ^2? as well as with K⁺ shows the human land use activities (namely, use of chemical fertilizers, disposal of domestic wastes, etc.), which add F^? to the groundwater. A significant number of the residents of the study area suffer from the health disorders related to fluorosis, which is a consequence of higher concentration of F^? in the drinking water. Thus, this study emphasizes the need for supply of safe drinking water, nutritional diet, rainwater-harvesting structures, and public education to realize “health for all” motto of World Health Organization.     

Growth of Prosopis juliflora on pegmatite tailings from Nellore Mica Belt, Andhra Pradesh, India

 Prosopis juliflora was found to be occurring extensively on the pegmatitic tailings. Leaves and twigs of P. juliflora and soil samples were analyzed for mineral elements. The analysis has shown variation in the absorption and accumulation of mineral elements of the same plant species growing at different areas. The plant species accumulated large concentrations of Sr, B, and Ba. The ubiquitous thorny shrub P. juliflora has an extraordinary ecologic amplitude and tolerance for a variety of elements. Received: 10 October 1997 · Accepted: 13 January 1998     

Geochemistry of groundwater in parts of Guntur district, Andhra Pradesh, India

Hydrogeochemical investigations, which are significant for the assessment of water quality, have been carried out to study the sources of dissolved ions in groundwaters of some rural areas of Guntur district, Andhra Pradesh, India. Groundwaters in the area are mostly brackish. High contents of SiO₂, and Na⁺ and Cl^- ions in groundwater, in comparison with those of seawater, suggests a meteoric origin of groundwater. The high concentration of SiO₂ and various geochemical signatures reflect the weathering of minerals. However, the Na⁺+K⁺ vs Cl^- ratio suggests weathering, has occurred only to some extent. The chemistry of groundwater favours the formation of clay minerals (montmorillonite, illite and chlorite), because of evapotranspiration. The positive saturation index of CaCO₃ and the high signatures of Ma²⁺:Ca²⁺ and Na⁺:Ca²⁺ reveals the occurrence of evaporation. The evaporation enhances the concentration of ions (which occurred originally in the water) in the soils during summer. The very high % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr % 0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8 % frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaqabeaadaaakeaacqqG % tbWucqqGpbWtdaqhaaWcbaGaeeinaqdabaGaeeOmaiJaeeyla0caaa % aa!2EC5! SO₄^{2 -} {\rm SO}_{\rm 4}^{{\rm 2 - }} and Cl^- contents in some groundwaters and the occurrence of kankar (CaCO₃) in the area suggest a long history of evaporation. Greater ionic concentration in the groundwaters of post-monsoon compared with pre-monsoon indicates the increasing addition of leachates into the groundwater from the soils in the monsoon and anthropogenic activities, which leads to a deteriorating quality of groundwater. According to the Gibbs' diagrams, rock weathering, to some extent, and evaporation are the dominant phenomena responsible for the higher ionic concentrations found in groundwater. Measures that benefit sustainable management of groundwater quality are suggested in this study.     

Groundwater quality in a coastal area: a case study from Andhra Pradesh, India

Over-exploitation of groundwater results in decline of water levels, leading to intrusion of salt water along the coastal region, which is a natural phenomenon. A groundwater quality survey has been carried out to assess such phenomena along the coast of Visakhapatnam, Andhra Pradesh, India. Brackish groundwaters are observed in most of the wells. The rest of the wells show a fresh water environment. The factors responsible for the brackish groundwater quality with respect to the influence of seawater are assessed, using the standard ionic ratios, such as Ca²⁺:Mg²⁺, TA:TH and Cl⁻:HCO⁻ ₃. Results suggest that the brackish nature in most of the groundwaters is not due to the seawater influence, but is caused by the hydrogeochemical process. Some influence of seawater on the groundwater quality is observed along the rock fractures. The combined effect of seawater and urban wastewaters is due to the inferior quality of groundwater in a few wells, where they are at topographic lows close to the coast.     

Hydrogeochemistry of the Sarada river basin,Visakhapatnam district,Andhra Pradesh,India

Systematic hydrogeochemical survey has been carried out for understanding the sources of dissolved ions in the groundwaters of the area occupied by Sarada river basin, Visakhapatnam district, Andhra Pradesh, India. Khondalites, charnockites and granite gneisses and calc-granulites of Precambrians and alluvial deposits of Quaternaries underlie the study area. Groundwaters are both fresh and brackish; the latter waters being a dominant. Most groundwaters are characterized by Na⁺:HCO₃⁻ facies due to chemical weathering of the rocks. Enrichment of Na⁺, K⁺, Cl⁻, SO₄²⁻, NO₃⁻ and F⁻ in some groundwater samples is caused by seawater intrusion, locally accompanied by ion-exchange, and anthropogenic activities, resulting in an increase of brackish in the groundwaters. Based on the results of this hydrogeochemical study, suitable management measures are recommended to solve the water quality problems.     

Vulnerability from storm surges and cyclone wind fields on the coast of Andhra Pradesh,India

The results presented here are from a study conducted for the government of the state of Andhra Pradesh (GOAP) in India, as part of a World Bank project on cyclone mitigation. A set of detailed maps were prepared depicting the Physical Vulnerability (PV), specifically storm surge inundation zones are shown for frequent occurrence, 50-year return period, likely scenario for global warming and extreme global warming. Similarly vulnerable areas from strong wind field from tropical cyclones (TCS) are also presented for the same four parameters. Vulnerability zones are presented from a social point of view also based upon certain socio-economic parameters that were included in determining the overall vulnerability of each Mandal in a coastal district (a Mandal represents a group of villages and towns) include: population, senior citizens, women, children under different age groups, type of housing, income level, cyclone shelters, hospitals and medical centres, schools and caste based population. The study is about scenarios that could happen if global warming and the predicted intensification of TCS actually occur as predicted by some numerical models.     

Regional appraisal of the fluoride occurrence in groundwaters of Andhra Pradesh

Fluoride (F^?) is essential for normal bone growth, but higher concentration in the drinking water causes health problems which are reported in many states of India. Andhra Pradesh is one of the states which suffer from excess fluoride in groundwater particularly in the hard rock terrain. In this context, a study was conducted in Andhra Pradesh based on chemical analysis of water samples from hydrograph net work stations (dug wells) and exploratory bore wells. The concentration of fluoride in groundwaters ranges from traces to 9.75 mg/l. The occurrence of fluoride is mostly sporadic, uneven and varies with depth. The highly affected districts include Nalgonda and Warangal in Telangana region, Prakasam in coastal region, Anantapur and Kurnool in Rayalaseema region. In certain areas of Nalgonda district, 85% of wells have fluoride more than permissible limit (> 1.5 mg/l) for drinking water. High F^? is present in all the geological formations, predominantly in granitic aquifers, compared to the other formations. The average value of fluoride is high in the deeper zone (1.10 mg/L), compared to the shallow zone (0.69 mg/L). The fluoride-rich minerals present are the main sources for fluoride concentrations in groundwater. Residence time, evapotranspiration and weathering processes are some of the other supplementary factors for high fluoride concentrations in groundwater. Long-term data of hydrograph net work stations (dug wells) reveal that fluoride concentrations do not show any marked change of trend with respect to time. The concentration of fluoride is found to increase with increase of Na⁺and HCO ₃ ^? , and decrease with increase of Ca²⁺. Sodium bicarbonate waters are more effective in releasing fluoride from minerals into groundwater. High fluoride waters are of Na⁺ type. The paper presents a brief account of the study and its results.