012846   Manglik A;Singh R N (NO, National Geophysical Research Institute, Hyderabad-500 007) : Rheological stratification of the Indian continental lithosphere: role of diffusion creep. Proc Indian Acad Sci-Earth Planet Sci 1999, 108(1), 15-21.

Dynamic recrystallization and reduction in grain-size at large strains, e.g. in shear zones, leads to rheological weakening of the lithosphere and facilitates intense ductile deformation. Includes this effect into the rheological models of the Indian continental lithosphere to analyse its role in modifying the rheological structure and strength of the Indian lithosphere. The results computed by using quartz and felspar rheologies for the upper and lower crust, respectively, and grain-size dependent olivine rheology for the upper mantle, indicate an increase in the ductility of the mantle lithosphere.

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012845   Mallik S;Venkata Chalam V;Govinda Reddy N; Sitaramayya T (Geological Survey of India, Chemical Division, , Bandlaguda, Hyderabad-500 068) : Comparative study of estimation of molybdenum in geological materials by icpaes and visual colorimetry methods. J appl Geochem 1999, 1(2), 105-9.

Molybdenum is one of the important and startegic element, the exploration of which demands analytical methods to estimate this element in geological samples at both very high and low levels. Molybdemum is estimated by visual colorimetry method in which the sample is decomposed by aqua regia and the organge red colour complex of molybdenum is developed with thiocyanate. This element is also estimated by ICPAES in sequential mode after decomposing the sample with sodium peroxide in zirconium crucible. These two methods are applied on geological standard samples and mineralised drill core samples from Harur in Tamilnadu and analytical data obtained from them are compared. It is observed that the visual colorimetry method is useful to detect molybdenum at low level of concentration (1.0-100 μg/g) and can be used to screen the samples for molybdenum exploration work where as ICPAES method can be used for mineralised samples.

012844   Maithani P B;Banerjee R;Panchal P K;Varughese S K;Ramachandran S;Rajendra Singh (Atomic Minerals Division, Department of Atomic Energy, , AMD Complex, Begumpet, Hyderabad-500 016) : Exploration for sandstone type uranium mineralisation in mesozoic basins of Gujarat : a hydrogeochemical approach. J Indian Ass Sedimentologists 1998, 17(2), 263-70.

Evaluation of hydrogeochemical data from Kachchh Mainland, Wagad and Wadhwan basins of Gujarat has indicated sudden drop of U, SO4^-- and HCO^-3 in slightly alkaline ground water along the palaeoslopes signifying a possible precipitation of uranium at redox interface in favourable host sandstones. Thus, by applying negative anomaly mode, target areas were selected for subsurface exploration of intercept uranium mineralisation along the hydrogeochemical fence in these basins. Initial reconnaitory drilling has shown persistence of oxidation zone even beyond 200 m depth with no significant mineralisation in Kachchh Mainland and Wagad basins whereas Wadhwan basin has indicated limited extent of oxidation and encouraging results (up to 200 ppm U) in host Than sandstones.

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012843   Madhavaraju J;Ramasamy S (Sedimentology Lab, Department of Geology, School of Earth and Atmosphe, University of Madras, Guindy Campus, Chennai-600 025) : Rare earth elements in limestones of Kallankurichchi formation of Ariyalur group, Tiruchirapalli Cretaceous, Tamil Nadu. J Geol Soc India 1999, 54(3), 291-301.

Studies on calcium carbonate (CaCO₃), trace elements and rare earth elements were carried out on the Kallankurichchi Formation in order to understand the elemental behaviour in marine limestones of the Tiruchirapalli Cretaceous. Variation in ∑REE content between Sandy Fossiliferous Limestone (SFL) and Fossiliferous Limestone (FL) can be explained as due to the varying amounts of terrigenous material present in the limestones. PAAS (Post Archaean Australian Shale) normalised REE patterns and La_N/Yb_N ((La_sample/La_shale) / (Yb_sample/Yb_shale)) ratios suggest that the terrestrial rocks are the major source for REE in these limestones. The SFL and FL show negative Ce anomalies, with slight variation between these limestones. The negative correlation between CaCO₃ and Ce/Ce^* values indicates that the observed Ce anomalies are not related to the CaCO₃ content in SFL and FL, whereas Ce/Ce^* values show positie correlation with detrital elements implying that the observed variations in the Ce anomalies resulted from the variation in the terrigenous material supplied by the continental area. SFL and FL show low U/Th ratio and U content. Low U contents suggest that the oxic condition prevailed in the bottom water and sediment column during the deposition of Kallankurichchi Formation.

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012842   Leelanandam C (Department of Geology, Osmania University, Hyderabad-500 007) : Petrographic and chemical appraisal, and regressive intrusive sequence in the Kondapalli layered complex, Andhra Pradesh, India. Indian J Geol 1999, 71(1-2), 5-13.

Kondapalli Layered Complex (KLC), a magmatic body slowly cooled under metamorphic conditions, comprises of two series: Chromitite-Ultramafic Rock Series (CURS) and Gabbro-Anorthosite Layered Series (GALS). No gradational units linking the two series are encountered, and hence there appears to be no continuum between the two. The subsidiary and primitive CURS was emplaced discordantly, subsequent to the concordant emplacement of major and evolved GALS into the enveloping charnockitic rocks. The mineral chemical data display a profound chemical hiatus between the two series. Pertinent petrographic and chemical features of the KLC are critically discussed with particular reference to the preservation of magmatic traits even during a strong metamorphic impress. It is suggested that the synmetamorphic KLC directly crystallised under granulite facies conditions without being metamorphosed in the prograde part of the metamorphic cycle, and that the early GALS and late CURS constitute a regressive intrusive sequence.

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012841   Kukillaya J P;Padmanabhan K;Krishnan E (NO, Kerala Samuhya Jalasechana Samithy, Thrissur-5, Kerala) : Use and limitations of short and medium duration pumping tests in understanding hard rock fracture aquifers - an example from Kerala. J Geol Soc India 1999, 54(3), 267-77.

Short and medium duration pumping test data from a well-field, in conjunction with outcrop fracture pattern studies, are used to understand the nature of a system of fracture aquifers in a metamorphic terrain in Kerala State. Satellite imagery shows a minor E - W elongation of the drawdown contours correlates with dominant E - W fracture sets seed on outcrops. The NNW - SSE fracture zone probably forms a regional conduit for groundwater flow, with the degree of hydraulic connectivity modified locally by other intersecting fracture zones. A large-scale heterogeneity in the form of an E-W fracture zone is indicated in this area. The pumping tests give responses similar to double-porosity and semi-confined models. Some data suggest localised linear flower near pumped well. Heterogeneity in fracture distribution results in a complex response to pumping. Certain broadly-defined zones and groundwater flow conditions are discernible within this heterogeneity.

012840   Khullar N K;Soni A;Jaspal Singh;Jaggi A K (Department of Civil Engineering, Punjab Agricultural University, Ludhiana-141 004) : Selection of rainfall frequency distribution model for Punjab. J appl Hydrol 1999, 12(4), 22-8.

Goodness of fit of three frequency distribution models, viz. Longnormal 3 - parameter. Longnormal 2 - parameter and Extreme value type I distribution has been tested for maximum 1 - day, maximum 2 - day and maximum 3 - day duration of rainfall data of Punjab by using Kolmorgov - Smimov test method. Two methods viz. method of moments and method of maximum likehood have been used for the estimation of parameters of these distributions. The analysis shows that Lognormal - 3 parameter distribution model using maximum likehood method of parameter estimation is the best fit distribution model for all three duration of rainfall.

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012839   Khazai E (Department of Civil Engineering, Faculty of Engineering, University of Sistan and Baluchestan, Zahedan, Iran) : Study of groundwater recharge in the Zahedan catchment, an arid region of south eastern Iran. J appl Hydrol 1999, 12(4), 1-14.

Investigates the hydrology and hydrogeology of the Zahedan catchment and illustrates the mechanisms contributing to the groundwater recharge. Based upon a suitable approach for estimating the groundwater recharge is recommended.

012838   Kar R K;Sahni A;Ambwani K;Singh R S (NO, Birbal Sahni Institute of Palaeobotany, 53, University Road, Lucknow-226 007) : Palynology of Indian onshore-offshore Maastrichtian sequences in India : implication for correlation and palaeobiography. Indian J Petrol Geol 1998, 7(2), 39-49.

Attempts to correlate the central Indian infra and intertrappean sediments with those of the subsurface Bengal Basin, the Krishna-Godavari delta and the Cauvery Basin by means of palynological fossils and comments on palaeobiogeographic implications. The intertrappean sediments of Mohgaon-Kalan, Padwar and Ranipur in Madhya Pradesh and Naskal in Andhra Pradesh have been palynologically investigated. The palynological data on Lameta, Bengal (sybsurface), Krishna-Godavari (delta) and Cauvery basins were reassessed. The result obtained from the foraminiferal and nannoplankton assemblages from these basins was also considered for correlation. It has been observed that Azolla cretacea, Ariadnaesporites sp., Gabonisporites vigouruoxii, Triporoletes reticulatus, Spinizonocolpites echinatus, Aquilapollenites bengalensis (=Striatriporites cauveriana) and Aquilapollenites indicus are present in most of the localities. With the help of these taxa, continental onshore and offshore sections can be correlated.

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012837   Kakde S B;Dugam S S (NO, Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pune-411 008) : Variability in the relationship of Indian summer monsoon rainfall and temperature anomalies on smaller spatial scale. Vatavaran 1998, 22(2), 21-33.

Indian summer monsoon rainfall is a thermally driven, large-scale circulation. Therefore it is logical to expect the dependence of the monsoon rainfall on the temperature. Many earlier studies have shown the dependence of the Indian summer monsoon rainfall on winter temperature anomalies over northern hemisphere and De-Bilt (Netherlands-52°06'N, 05°11'E). Most of these studies are confined to the relationship between temperature anomalies and monsoon rainfall over India as a whole. An attempt has been made to understand the spatial variability in the relationship between the monsoon rainfall and temperature anomalies. De-Bilt temperature anomaly in the month of January and northern hemisphere surface air temperature anomaly in winter [(J+F)/2], for the period over various meteorological sub-divisions and five homogeneous regions of India have been observed. The correlation analysis reveals the spatial variability in the relationship between the monsoon rainfall and temperature anomalies. The relationship is statistically significant for Peninsular India, North-West India and West-Central India. More number of sub-divisions show statistically significant relationship between the monsoon rainfall and temperature significant relationship between the monsoon rainfall and temperature anomalies in the month of January over De-Bilt. On smaller spatial scale, the monsoon rainfall over larger area of Indian subcontinent is under the influence of De-Bilt temperature...

012836   Joy Chandra Singha L;Das P K;Phukan P (Department of Geological Sciences, Gauhati University, Guwahati-781 014) : Textural parameters of barail sandstones occurring around Sonpur, Jaintia hills, Meghalaya. J Indian Ass Sedimentologists 1998, 17(2), 197-211.

Grain size analysis of unconsolidated to semi-consolidated Barail Sandstone (Oligocene) in a part of South Jaintia Hills district of Meghalaya around Sonapur indicates that the sediments are mostly medium to very fine Grained (av size 1.756φ to 3.483φ suggesting fluctuation of energy condition during deposition. The sediments are poorly to moderately sorted (standard deviation 0.746φ to 1.295φ, while a very positively skewed nature of the population is evidenced by long tail at the finer end (Ski-0.223 to 0.77). The sediments are very leptokurtic to mesokurtic (0.916 to 2.017). The variable addition of finer grains into the coarser mode impart leptokuritc character to the distribution of grain size. On the whole, the sediments are bimodal. The textural classification of the sediments fall under silty sand category. The mutual relationships of grain size parameters indicate a fluviatile condition of deposition. Log-probability plots show delta distributary channel characteristics. The C-M pattern worked out for the evaluated samples suggests deposition by graded suspension under river or tractive current hydraulic regime.

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012835   Hasan M A;Woobaidullah A S M;Ahmed K M;Rahman M M (Department of Geology, University of Dhaka, Dhaka 1000, Bangaldesh) : Geochemistry and origin of saline ground water in Manda Thana, Naogaon district, NW Bangladesh. Indian J Earth Sci 1997, 24(3-4), 26-32.

Saline ground water at a relatively shallow depth in the study area, far away from the present day coastline, is considered to have originated under an ancient hydrogeological influence, i.e., salinity related to hydrogeological entrapment of sea water. Occurrence of NaHCO₃-type water indicates areas of freshening, i.e., active flushing of the aquifer by fresh recharge water which is more active in the upper part of the aquifer. On the other hand, restricted circulation with very low flushing action by recharge results in the occurrence of NaCl-type brackish water. Interpretation of hydrogeochemical data suggests ion exchange, simple dissolution and mixing are the dominant geochemical processes active in aquifer.

012834   Gupta A (NO, , 200, Santoshpur Avenue, Calcutta-700 075) : Hummocky cross-stratification in Chhattisgarh basin, M.P. and its hydraulic and bathymetric implications. J Indian Ass Sedimentologists 1998, 17(2), 213-24.

Proterozoic sediments of the eastern part of the Chhattisgarh Basin registers six distinct hummocky cross-stratified facies units. Scour and drape type and non-erosional based growing bed forms, both types of hummocky cross-stratification have been observed. The large dimension of hummocks, upsweeping of laminate, sigmoidal nature, broadly undulating erosive and flat base, draping and partial preservation of storm sequence i.e. BPHFX probably suggest intense storm activity (midlatitude winter storm) in shelf region and the water depth was probably of the order 1-30 m. Absence of vegetal cover and sedimentation style, projects a picture of vast barren plains presumably swept by strong winds/storms, which circulated unimpeded.

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012833   Golani P R;Pandit M K (A.M.S.E. Wing, Central Zone, GSI, , Seminary Hills, Nagpur-440 006) : Evidence of epithermal activity and gold mineralization in Newania Carbonatite, Udaipur district, Rajasthan. J Geol Soc India 1999, 54(3), 251-7.

Geological, geochemical and C- and Pb-isotopic evidence available on the Newania Carbonatitic Body (NCB) in southern Rajasthan are not entirely incontrovertilble from the point of view of carbonatite magmatism. Based on recognition of calcite-lined vugs, `dog-tooth spar' and `jigsaw puzzle' structure, the hematite bearing ankeritic carbonates (the ankeritic `carbonatite') are considered as epithermal emplacements into dolomitic (magnesipo) carbonatite. Seven samples collected from hematite bearing ankeritic (±sideritic) carbonates, which constitute an important component of the NCB, have given gold values ranging between 0.93 to 1.36 ppm. The significance of this find lies in the association of gold with oxides and carbonates of hydrothermal affinity.

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012832   Elampooranan T;Rajmohan N;Abirami L (Dept. of Chemistry Govt. College, , Kumbakonam-612 001) : Hydrochemical studies of artesian well waters in Cauvery Deltaic area, South India. Indian J envir Hlth 1999, 41(2), 107-14.

Artesian well waters of the deltaic area of Cauvery basin were analysed for pH, EC, Ca, Mg, Na, K, De, F, B, SO₄, Cl, DO, TH and TA to assess the suitability of these waters for domestic use based on the WHO standards. SAR, RSC and Na% values were calculated to assess the suitability of these waters for irrigation. Most of these waters were found unsuitable for both domestic and irrigational applications.

012831   Dhanamjaya Rao E N;Sreenivasa Rao P (Department of Geology, Andhra University, Visakhapatnam-530 003) : Organic matter and calcium carbonate in modern sediments of the Godavari delta and pro delta, East coast of India. J Indian Ass Sedimentologists 1998, 17(2), 177-85.

Forty-five sediment samples collected from different sedimentary environments of the Godavari delta were analysed for texture, organic matter (OM) and calcium carbonate (CaCO3) contents. The organic matter values vary widely, ranging from 0.26 to 6.29 percent and CaCO3 varies from 5.0 to 33 percent. The high organic matter is associated with fine grained fractions and low OM content with sand and sandy silts. The carbonate content shows inverse relationship with grain size and progressively increase from upper delta plain to prodelta environments. The CaCO3 content vs OM are inversely related. Such a relationship is possibly due to the presence of molluses, foraminiferal test and other biogenic materials. Benthic and planktonic foraminiferal tests are the ultimate source of CaCO3 in the prodelta.

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012830   Debaje S B;Ramachandran T V (NO, Indian Institute of Tropical Meterology, Pune-411 008) : Variation of radionuclides levels present in the ambient air with surface meterological parameters in Pune. Indian J envir Prot 1999, 19(7), 530-40.

Results of the airborne thoron (Rn²²⁰) concentrations measured in an outdoor environment by grab sampling method carried out at Indian Institute of Tropical meteorology (IITM). Pune (18° 32' N, 73° 51' E, 559 m a.m.s.I.) during May, 1993 to August, 1994 is presented. Results indicate seasonal significant changes in Rn²²⁰ concentration with respect to soil temperature and surface meteorological parameters. From this study it was found that the Rn²²⁰ concentrations reaches a maximum during local winter months (January to February) and have a close relationship with surface meteorological parameters and soil temperature at different depths.

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012829   Dayal A M;Hussain S M (NO, National Geophysical Research Institute, Hyderabad-500 007) : Sr-Nd isotopic composition of lamprophyre dykes from Queen Maud Land, East Antarctica. Curr Sci 1999, 77(12), 1681-5.

Alkali basaltic-lamprophyric dykes intrude precambrain gneisses in the Schirmacher Oasis, Queen Maux Land, East Antarctica. Rb-Sr and Sm-Nd isotopic data on two lamprophyre dykes are reported from the Schirmacher Oasis. The lamprophyre dykes have given Rb-Sr biotite/whole rock isochron age of 439 ± 10 Ma (2σ). Large variations in εSr and εNd indicate higher degree of crustal assimilation. Higher εSr (+54 to +72) and lower εNd (-7 to -13) of these dykes also suggest that the source was contaminated by older crust. Biotite/whole rock Rb-Sr isotope data on lamprophyre dykes show that the terrain was affected by thermal event during early Paleozoic which is correlated with the end of Pan-African orogeny.

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012828   Das S;Kar A (NO, , 18, Madhusudan Nagar, Bhubaneswer-751 001) : Hydrogeology around Sukinda Valley, Orissa with reference to mining activities. Indian J Earth Sci 1997, 24(3-4), 10-25.

Chromite bearing ultramafic rock bodies in Sukinda valley, cover an area of about 50 sq km in Cuttack and Dhenkanal districts of Orissa. Excessive ground water seepages occur in the opencast mines creating mining problems. The problems are relatively acute in the eastern sector of the valley. Sporadic occurrences of high hexavalent chromium also have been reported from groundwater in the area. In this context studies were carried out in the valley to know the hydrogeologial conditions and hydraulic behaviour of aquifers in order to cope up with the problems likely to be faced with extension of mining. Geologically the area is underlain by a laccolithic ultramafic complex highly weathered in the east. The studies reveal the laterites, weathered and fractured ultramafics in the area from a hydraulically interconnected aquifer system. Groundwater occurs generally under uncofined to near unconfined conditions. Groundwater flows by gravity drainage from laterite-weathered zone aquifer to the structural planes of unaltered and partially altered ultramafic bodies at depth. The deppth to water table ranges from 2.73 to 11.89m in pre-monsoon and 0.62 to 8.19 m in post-monsoon periods. The zone of saturation extends down to 65 m depth....

012827   Das A;Bhattacharyya C (Department of Geology, University of Calcutta, 35, Ballygunge Circular Road, Calcutta-700 019) : Amphibolites from Tulin-Jhalida area, Puruliya district, West Bengal. Indian J Geol 1999, 71(1-2), 143-61.

Precambrian amphibolites of Tulin and Jhalida areas occur as small bodies associated mainly with the two predominant rocks, granitoid gneisses and calc-silicate (diopside rich) gneisses. They have been classified into ortho- and para-types, mainly on the basis of relict igneous plagioclase laths commonly present in a great majority of the samples, petrography, and chemical plots of selected samples in Leake's discrimination diagrams. Most of the amphibolites are ortho-amphibolites, which have been further classified as green hornblende ortho-amphibolite, green-brown hornblende ortho-amphibolite and yellow-brown hornblende ortho-amphibolite. The petrographic distinctions among these three types of ortho-amphibolites and also between ortho- and para-amphibolites have been attempted; generally, most of the ortho-amphibolites are massive or poorl schistose, while all the para-amphibolites are strongly schistose. Hornblende chemistry does not permit to distinction between ortho- and para-amphibolite, because in one sample of ortho-ampihibolite it is magnesiohornblende, while both magnesio-hornblende and ferro-hornblende are present in para-amphibolites. Plagioclase is only statistically more calcic in ortho-amphibolite than in the para-amphibolite. The parent material of ortho-amphibolites is of tholeiitic composition, as seen in the relevant major and/or trace element discrimination diagrams. In places, the amphibolites have been migmatised to varying degrees. The petrography and major element chemistry of these migmatites suggest that they have been formed by injection of granitic magma in the amphibolites. The paleosome of such migmatites is suggested to be of basaltic composition, and not trachyandesitic to andesitic, as previously suggested.

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012826   Chattopadhyay S;Chattopadhyay B;Gupta A K (Geological Survey of India, , Calcutta) : Preliminary phase equilibria study of the system nepheline-diopside-sanidine under 1 Kbar in presence of excess water. Indian J Geol 1999, 71(1-2), 81-91.

System diopside-nepheline-sanidine, a join of the quinary system, NaAISiO₄ -KAISiO₄-CaO-MgO-SiO₂ was studied at 1 kb and variable temperatures. It is established that the join cuts through the primary phase volumes of diopside solid solution (Di_ss). There are two four-phase points : one occurring at Di₂₆Ne₆₆ San₈ and 990±10°C (C) and the other at Di₁₁Ne₃₁ San₅₀ and 865±5°C (J). In the first case (C), Di_ss + Fo_ss + Ne_ss + L are in equilibrium, whereas in the second case (I), Di_ss + Ne_ss + Lc_ss + L coexist in equilibrium. The assemblage, Di_ss + Ne_ss + Lc_ss + San_ss + L occurs at 640±10°C. Near the diopsidenepheline join, all compositions show the appearance of a pargasitic amphibole as an additional phase. Preliminary studies at 10 kb indicate complete elimination of leucite. Experimental study of the system suggests the following two paragenetic sequence of crystallization:- 1. Mela-nephelinie → Olivine nephelinite → nepheline-bearing leucitite → nepheline liucitite phonolite → nepheline phonolite → nepheline-pargasite phonolite. 2. Leucitite → nepheline leucitite → nepheline leucite pholonite → nepheline phonolite.

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012825   Chandrasekar N;Sivakumar V;Udayanapillai A V; Rajamanickam G V (Department of Geology, V O Chidambaram College, Tuticorin-628 008) : Heavy metal concentrations in salt marsh sediments of Tuticorin, Tamil Nadu. J Indian Ass Sedimentologists 1998, 17(2), 245-50.

Avecinnai Officinalis (Spartina) plants from salt marsh area of Tuticorin were collected. The roots, stem and leaf of the plants were analysed for Cu, Zn and Ni. The concentrations of metals were found to be higher in leaves than the stem and roots except for Ni. Sediments from the nearby industrial area show higher concentrations of Cu, Zn and Ni which could be attributed to the intensity of anthropogenic inputs.

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012824   Bose M K;Roy Moulick S K (Department of Geology, Presidency College, Calcutta-700 073) : Petrology and geochemistry of the metabasic rocks of Khammam schist belt, south of Chimal Pahad complex, Andhra Pradesh. Indian J Geol 1999, 71(1-2), 15-32.

Geochemistry of the Khammam amphibolites and granulites strongly indicates their affiliation to Group II and Group B basic granulites of Madras area which are surmised to have cumulation controlled compositions. However, Khammam metabasic suite does not bear any evidence of strong crystal fractionation. The Khammam amphibolites and granulites have an overall depletion in incompatible elements and, particularly, in HFS elements, relative to MORB. Mantle normalised NME plots for the metabasics reveal a Th-Nb hiatus as also negative Nb, Zr, Ti and Sr anomaly; these often characterise contaminated boninitic magmas. Chondrite normalised REE profiles of the Khammam metabasics show a disc shaped form (characteristic of boninite) or a very weakly fractionated (La_N/Yb_N = ca. 1.66) pattern. The garnetiferous mafic granulites show moderate LREE fractionation (La_N/SmN = ca.3.7), but an almost chondritic HREE profile. The tonalite-trondhjemite granulite associated with the Khammam metabasics also has depleted HREE chemistry in comparison to tonalitic granulite of Madras area and OMTG of Singhbhum craton. However, in contrast to these acid granulites, the Khammam tonalite shows a strong LREE fractionation (La_N/Nd_N =30.5), though there is no evidence of late alkaline metasomatic activity in the terrain....

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012823   Biswas S K;Agarwal R P (NO, , 6, Sidhartha Enclave, Gen. Mahadev Singh Road, Dehradun-248 001) : Tectonic framework of coastal sedimentary basins and evidences of recent neotectonic movements in Indian Peninsula, South of 15° latitude. Indian J Geol 1999, 71(1-2), 117-32.

Geomorphologically, the south-western coastal basins have three broad geomorphic units, i.e., Coastal Plain, Lateritic Upland/Pediplain, and Dissected Hills and Scarp-land. The dominant lineament trend is NNW-SSE to NW-SE with subsidiary ENE-WSW and N-S trend. ENE-WSW trend is related to major arches and extend into offshore, segmenting the offshore basins in transverse blocks. The south eastern coastal basins show four broad geomorphic units, viz., Marine Plain, Deltaic Plain, Lateritic Upland Pediplain, and Dissected Scarp-land. Dominant lineament trend is NE-SW and ENE-WSW with NW-SE and N-S subsidiary trend, and these have shaped the eastern coast line in different segments. Neotectonic evidences are observed all along the south-western and south-eastern coastal basins in the form of raised beaches, sudden break in slope, drowned river valleys, fluvial terraces, submerged shore lines, and truncation of beach ridges etc. Three planation surfaces at elevations of 180-100 m, 80-40 m and 20-03 m are identified in the south-western coastal basins. The three planation surfaces in the south-eastern coastal basins occur at elevations of 300 m, 150-50 m and 50-30 m. These surfaces represent the neotectonic cycles in these basins.

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012822   Biswas R K;Ghosh R K (Department of Soil and Water Engineering, Faculty of Agricultural Engineering, Bidhan Chandra Krishi Viswavidyal, Mohanpur-741 252) : Evaluation of estimation of evaporation losses of water from bare soils using soil-water diffusivity. J appl Hydrol 1999, 12(4), 39-45.

Soil-water diffusivities (D) were determined for the different soil moisture contents (θ) of Memari loam in Bardhaman district of West Bengal. The mean soil-water diffusivity (D) was 10.5439 cm²/day. Evaporation from the soil in two consecutive years of 1992-93 and 1993-94 were determined by using soil-water diffusivities following Crank (1956) and actual measurement of moisture depletion by sample collection from field soil. The deviation was found only 13.256% from the actual which suggests that soil-water diffusivity may be suitably used for the estimation of moisture losses from bare soils.

012821   Biswas A K;Dotiwala (NO, K.D. Malaviya Institute of Petroleum Exploration, ONGC, Dehradun-248 195) : Occurrence of overpressure in Cachar foldbelt area. Indian J Petrol Geol 1998, 7(2), 27-38.

Oil and Natural Gas Corporation Ltd. (ONGC) has so far explored eight exposed anticlines and five concealed structures in the Cachar foldbelt area. Overpressure has been encountered in nine of them. Study analyses the occurrence of overpressure in the context of six geological factors, e.g., depth, stratigraphic level, structural position, position of major thrust fault, outcropping formation in the core of the structure and thickness of the transition zone. The analysis reveals that the overpressure in Cachar are generally confined to overthrusted Middle Bhuban Formation in the crestal wells and occurs rarely below 3000m. Further, younger the formation outcropping in the core of the structure, deeper is generally the top of overpressure. Majority of the overpressured wells in Cachar are characterised by multiple overpressure regimes and relatively thin transition zones.

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012820   Bhandari A;Chatterjee T K;Vig K C;Juyal N P; Pundeer B S (NO, KDM Institute of Petroleum Exploration, ONGC, Kaulagarh Road, Dehradun-248 195) : Biostratigraphy, source rock potential and depositional model of basal oligocene pay sands in Ichapur-Shantipur area, West Bengal basin, India. Indian J Petrol Geol 1998, 7(2), 1-14.

Biostratigraphic and sedimentological studies carried out on Burdwan Formation (Early Oligocene) in Ichapur-Shantipur area of West Bengal Basin suggest that the sands of Golf Green Member were deposited under marginal marine to shallow inner shelf environment in fluvial dominated regime of constructive delta. The overlying Memari Member was deposited in middle to outer shelf (bathymetry 50-100m) environment under anoxic condition. The top of Memari member is marked by regression with a drop in relative sea level of about 100m. The source rock studies from this part of Bengal Basin reveal that in Ichapur area, the Eocene to basal Oligocene succession has marginal to good source potential for generation of hydrocarbons while in Shantipur and Golf Green areas, the Oligocene sediments are immature and Eocence section shows marginal source potential.

012819   Bhadra B K (Department of Earth Sciences, Pondicherry University, Pondicherry-605 014) : Phyllonites from Attur Shear Zone and its tectonic significance in Southern Granulite Terrain, South India. Curr Sci 1999, 77(12), 1685-7.

In the eastern part of the Southern Granulite Terrain, Attur Shear Zone (ASZ) is characterized by 1 to 1.5 km wide phyllonite zone which shows the maximum intensity of shearing. The foliation planes in this zone are sub-vertical ENE-WSW striking mylonitic foliation with dominant steeply plunging (70-80°) stretching lineations. The phyllonites show all gradations from protomylonite to ultramylonite and extensive biotitization of pyroxene/hornblende minerals. The microstructural studies of phyllonites indicate that ASZ has undergone extensive ductile shearing accompanied by fluid (H20) induced retro-grade metamorphism. ASZ, probably formed at deep (10-15 km) continental crust, is exhumed at the present level of erosion by relative upliftment of adjacent blocks.

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012818   Baruah J;Baruah N K;Kotoky P;Sarma J N (Geoscience Division, R R L (CSIR), Jorhat-785 006) : Geochemistry and environmental evaluation of the Jhanji river sediments, Assam. J Indian Ass Sedimentologists 1998, 17(2), 271-85.

Chemical characteristics and their porbable impact on the environment have been studied in the Jhanji river sediments. The physicochemical parameters show an increasing trend in the monsoon period than the non-monsoon periods. The metal concentration, except Fe, decreases towards downstream. The suspended sediments are more rich in metal content than the bed sediments. The concentration levels of Al, Mn, Zn, Cr, Co, Cd and Ni in upsteam part is higher than the background values. The pollution load index is moderately stable over the basin and shows a downstream decreasing trend.

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012817   Bandyopadhyay S (Department of Geography and Environmental Management, Vidyasagar University, Medinipur-721 102) : Coastal erosion and its management in Sagar Island, South 24 Parganas, West Bengal. Indian J Earth Sci 1997, 24(3-4), 51-69.

Sagar island (Hugli estuary : 21°37'-57'N, 88°02'-11'E) was started to be reclaimed from the Sundarban mangrove wetlands in 1811. Mainly due to different Government policies the island gradually became almost completely settled with a population of 149,222 (1991), naturally growing at 3.99% per year. Coastal erosion, that reduced the total supratidal area of Sagar by about a quarter within 144 yr (from 284.55 kM² in 1851-55 to 219.26 km² in 1997), forms the most important natural environmental hazard (NEH) affecting the island. Among other things, the erosion can primarily be related to the disturbance of morphological steady state of the Hugli estuary due to reclamation of its intertidal areas. Most of the erosion takes place episodically during tropical cyclones - the severe types of which (Beaufort force 10 or above) have a recurrence interval of 3.28 years within 100 km of the island. The erosion management schemes of Sagar, managed by seven different agencies, include 74.5 km of marginal embankments (19.4% brick-paved), 579 ha of mangrove plantations in 11 localities and three relocation settlements. Their efficiency range from excellent to very poor. To ameliorate the existing schemes, the available resources need to be used more rationally and optimally with proper appreciation of the natural feedback mechanisms....

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012816   Ashok Kumar;Venkatachala B S (NO, 1 Wadia Institute of Himalayan Geology, Dehradun-248 001) : Proterozoic Chert microbiota from the Riasi inlier of the Vaishnodevi limestone in the Himalayan foothills, Jammu, India. Indian J Petrol Geol 1998, 7(2), 51-70.

Well preserved biota has been recovered from the thin black chert laminae occurring in sparse and sporadic patches in the Riasi inlier of Vaishnodevi Limestone cropping out in the Lower Himalaya, Jammu. The biota is dominated by mat forming crustose, coccoid, chroococacean cyanobacteria that formed large colonies including Eoentophysalis belcherensis and Palaeopleurocapsa wopfnerii. Myxococcoides grandis is also a dominant taxon. Other coccoid taxa occur scattered between the crustose colonies as minor components. These include Gloeodiniopsis lamellosa, Eogloeocapsa avzyanica, Sphaerophycus cf. S. medium and Eosynechococcus moorei and E. grandis. Filamentous oscillatoriacean cyanobacteria occurring tangled amidst this assemblage include Siphonophycus Kestron, Siphonophycus robustum and Oscillatoriopsis sp. besides Circumvaginalis elongatus, Archaeoellipsoides major and A. minor. The biota are associated with spongy yellowish brown amorphous as well as grey amorphous and sapropelic organic matter. It is considered that the cyanobacterial mats discussed here grew in warm hypersaline waters in a shallow shelf regime.

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012815   Anil Kumar (Agricultural Engineering Hill Campus, G B Pant University of Agriculture and Technology, Ranichauri, Tehri Garhwal-249 199) : Appropriate water resource management to boost the productivity of rainfed agriculture in Garhwal Himalaya. J appl Hydrol 1999, 12(4), 46-51.

Studies at the Hill Campus of G B Pant University of Agriculture and Technology, located at about 2000 m above mean sea level in Tehri district have shown that the dug-out farm ponds lined with 0.25 mm thick Low Density Poly Ethylene (LDPE) sheet is a technically feasible and economically viable technique in the region. Such ponds have life span of about 12 years and the harvested water has multiple uses as for supplemental irrigation in cereals and vegetable crops, forest nurseries, orchards and medicinal and aromatic plants; consumption by livestocks and performing household activities. Due to topographical constraints, the capacity of the ponds varies between 5m³ and 15 M³ only having inverted prismoidal shape with 1 m depth and side slopes of 1.5:1 to 2:1 depending on the type of soil. The cost of construction of such ponds comes out to be Rs. 100 per m³ storage of water. This technique is quite appropriate to the farmers as it can be constructed and maintained by themselves with affordable cost.

012814   Ahmad S;Nagi D C (School of Environmental Sciences, Jawaharlal Nehru University, New Delhi-1100 67) : Hydrogeomorphological mapping for groundwater prospecting using IRA-IA LISS2 images : a case study of eastern Orissa an area between the Baitrani and Subarnrekha river. J appl Hydrol 1999, 12(4), 35-8.

Eastern part Orissa face acute potable water shortage and this area is one of the highly drought prone area of the India. The groundwater resources in the basin have not been adequately exploited. The present investigation was undertaken to evaluate the groundwater promised zones. IRA-IA, LISS2 and false color composite of band 2,3,4 were interpreted visually to differentiate different geomorphological unit and to delinerate the major trend of the lineament . The distinct geomorphic feature distinguish linear ridge, residual hill, vegetational anomaly, paleochannel, structural lineament. The study shows that paleochannel, intersection of structure lineament and residual hill are assuring zones for groundwater prospecting.

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012813   Agunwamba J C (Dept. of Civil Engineering, University of Nigeria, Nsukka) : Field erosion study and model verification. J Indian Ass Envir Mgmt 1999, 26(2), 91-9.

Erosion study was undertaken at the old Government Residential Area in Port Harcourt, Rivers State, Nigeria on a terrain of low vegetation density with an area of 68.00 m². Analysis classified the soil as silty sand with low infiltration capacity. The average specific gravity, cohesion and angle of internal friction were 2.28, 66.67 KN/m² and 27.95° respectively. Data on soil loss and the amount and duration of rainfall were collected between September 1991 and May 1992. The run-off coefficient was found to be 0.3152. There was a good linear relationship between the rate of soil erosion and the rainfall intensity with a coefficient of correlations (r) and standard error (se) of 0.982 and 0.005 respectively. Verification of Laboratory and field soil loss equations with laboratory and field data respectively revealed some disparity between measured and predicted values, especially in the laboratory model. The predictive capacity of the laboratory model, an exponential model proposed by Umeh and Ojiako was improved considerably when A (Detachment capacity of flow) was expressed as a function of slope and soil density and rate parameter (α) expressed in terms of velocity and slope. With A and a assumed constant as in Ume's and Ojiako's equation, the values of r and se are 0.227 and 0.327 respectively, whereas with A and α regarded as variables, the corresponding values were 0.978 and 0.072 respectively. Generally, Komura's showed evidence of good predictive capability when, verified with field data. However, this was not obtained at low rainfall intensities (<60> 2mm/hr) because of the assumption of constant momentum coefficient (β) which rather increases with decreasing rainfall intensity and the omission of interrill detachment term which will usually be predominant for low flows.

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012812   Agrawal P K;Pandey O P (Theoretical Geophysics Group, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007) : Was there an intracontinental rift between India and Sri Lanka. J Geol Soc India 1999, 54(3), 237-49.

Nature of tectonic configuration between SE coast of India and NW coast of Sri Lanka has been a subject of considerable debate for over past two decades. Analyses long wavelength gravity-magnetic, seismological, satellite imagery and related tectonic, geologic and geomorphic information over India, Madagascar, Sri Lanka and Antarctica to suggest that no intercontinental rift could ever develop between India and Sri Lanka. It appears that in the erstwhile Gondwana land, Sri Lanka rested in the Lutzo-Holm Bay of Antarctica and had the same relative paleoposition with respect to India as it has today, although a small scale translational and rotational motion as suggested by Yoshida et al (1992) may not be ruled out. The study throws significant light on the paleoassembly of these continental fragments ad suggests the possibility of weak mantly upwelling between India and Sri Lanka which may have resisted the formation of oceanic crust between them.

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012811   Agarwal R P;Prasad D N;Srivastava A K; Maithani A (NO, ONGC, 3rd Avenue End, Society Area, Clement Town, Dehra Dun) : Structures of Western Himalayan foothills - a case study on application of remote sensing techniques in exploration. Indian J Petrol Geol 1998, 7(2), 15-26.

Western Himalayan Foothill Belt has been extensively mapped by systematic geological field work by the geologists of Oil and Natural Gas Corporation. The major structural trends mapped are mostly parallel to the Himalayan structural trend and some of the cross trends mapped follow the swales and recesses. Availability of the high resolution remote sensing Thematic Mapper (TM) data has added a new dimension to the structural geology by providing a better regional perspective. It is inferred that horizontal displacement is apparent along these major lineaments trends. The NNW-SSE trending lineaments show right lateral movement whereas, the E-W trend shows left lateral movement. Divergent pattern of structural trends and northward swing of Main Boundary Thrust and its proximal thrusts along these lineaments suggest them to be deepseated/basement involved faults. Gravity and magnetic data also corroborate the above interpretation. The movement along these lineaments resulted in the formation of structurally complex and higly deformed zones (HDZ) whereas the intervening areas constitute less deformed zones (LDZ).

011754   Yamuna Singh;Chabria T (Atomic Minerals Directorate for Exploration and Research, Department o, , Begumpet, Hyderabad-500 016) : Late archaean-early proterozoic Rb-Sr isochron age of granite from Kawadgaon, Bastar district, Madhya Pradesh. J Geol Soc India 1999, 54(4), 405-9.

Whole-rock Rb-Sr analysis of ten granite samples from Kawadgaon, Bastar craton, yield an isochron corresponding to an age of 2497±152 Ma (2σ) and initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7142±0.0100(2σ). The data suggest emplacement of Kawadgaon granite during the ca. 2500 Ma Archaean-Proterozoic transitional event in the craton.

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011753   Srinivasa Rao;Rao A T;Krishna Rao S (Department of Geology, Andhra University, Visakhapatnam-530 003) : Geoarchaeological study in Penner delta, east coast of India. Curr Sci 1999, 77(9), 1189-96.

Two generations of laterites (primary and secondary) are identified in the Penner delta and the archaeological evidence comprising handaxes and flake archaeological evidence comprising handaxes and flake tools is collected from the surface of the laterites. The heavy handaxes are classified as ovate, cordate and lanceolate types and they are contemporary to the early Upper Pleistocene. The flake tools were introduced after the 3rd interglacial period when there is change in climate. The laterites from the Penner delta in the Nellore region are older than the Pleistocene.

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011752   Singh R P;Mishra N C;Prasanjeet Dash;Mohrana B K (Department of Civil Engineering, Indian Institute of Technology, Kanpur-208 016) : Snow characterization using SSM I data. Curr Sci 1999, 77(9), 1180-4.

Snow in the Himalayan region is a vital water resources for India. Most of the river systems of India are dependent on melting of snow during summer months, which gives substantial amount of water for agriculture and hydropower, and a boost to development. But the changes in snow cover have direct relation to global climatic changes. It is expected that the surface and atmospheric temperatures may significantly change which may influence the snow cover over high altitude regions. Currently, much attention is being paid to the global warming trend due to the increase of greenhouse gases in the earth's atmosphere. The mapping of snow cover using optical sensors, however, suffers quite often with cloud problems. Such problems do not affect microwave remote sensing which has an added advantage off quantitative estimation of snow parameters and characterization of snow cover. An attempt has been made to study the characteristics of brightness temperature of snow over Himalayan region using SSM/I data.

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011751   Sharma A K;Seshadrinath S T;Sinha R P;Naidu P V S (Atomic Minerals Directorate (AMD) for Exploration and Research, Depart, , Hyderabad-500 016) : Silver in the uraniferous limestone at Gogi, Bhima basin, Gulbarga district, Karanataka. J Geol Soc India 1999, 54(4), 432-3.

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011750   Rachna Raj;Maurya D M;Chamyal L S (Department of Geology, Faculty of Science, M S University of Baroda, Vadodara-390 002) : Tectonic geomorphology of the Mahi river basin, Western India. J Geol Soc India 1999, 54(4), 387-98.

Neotectonic activity along pre-Quaternary tectonic trends has played a major role in the evolution of Mahi drainage basin. The Mahi basin is controlled by NE-SW and WNW-ESE Aravalli trend in the uplands and by NNW-SSE Tertiary basement faults in the distal part. Lineament analysis shows three structural trends in the area which are related to major regional tectonic trends. Stream orientations indicate that the NNE-SSW and NNW-SSE trends represent lineaments which were active during the youngest tectonic phase. The NE-SW and WNW-ESE trends are asightly older. The evolution of overall configuration of the basin is attributable to neotectonic activity along WNW-ESE and NE-SW trends which have been modified by a later phase to tectonic activity along NNW-SSE trend. Morphotectonic analysis has been helpful in assessing the relative degree of tectonic activity in the different geomorphic zones of the Mahi river basin. An increasing degree of tectonic activity towards the NE conforming to the northeastward extension of the Aravalli range where the central axis of the range lies, has been indicated.

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011749   Purnachandra Rao N (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007) : Single station moment tensor inversion for focal mechanism of India intra-plate earthquakes. Curr Sci 1999, 77(9), 1184-9.

Single station moment tensor inversion of the nearest broadband station data can be effectively used to obtain fairly accurate focal mechanism solutions for small to moderate earthquakes, as demonstrated for the 21 May 1997 Jabalpur earthquake (Mw 5.8). The method is also applied to study the 3 February 1999 Godavari valley earthquake (Mw 3.6) using broadband data of the Geoscope station, Hyderabad. A pure strike-slip solution is obtained with strike 326°, dip 88° and rake 2°. The active tectonics of the Godavarii graden is studied using this result in conjunction with the mechanism of the 13 April 1969 Bhadrachalam earthquake (Mw 5.7), which also occurred in the same region. The fault planes of the two earthquakes are correlated with lineaments from Landsat images and the possibility of a block rotation in this region is suggested.

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011748   Pant P D;Luirei K (Department of Geology, Kumaun University, The Durham, Nainital-263 002) : Malpa Rockfalls of 18 August 1998 in the northeastern Kumaun Himalaya. J Geol Soc India 1999, 54(4), 415-20.

Case history of Malpa rockfall of 18 August 1998, which has claimed a toll of 250 lives, including 60 pilgrims in transit camp, under the shadow of Malpa peak, 40 km north of Dharchula. The slope failure which caused the rockfall was aggravated by high angle of hillslope (78°), conductive conditions of bedrock, particularly enlarged joint space and proximity to the Main Central Thrust (MCT), which has been affected by neotectonic movements in the recent past. High frequency of discontinuities have severely deteriorated the stability of hillslopes and their safety factor `F' has been reduced to 0.114. The rockfall vector shows a close parallelism with the geometrically determined wedge failure responsible for rockfalls. The rockfall occurred in the metaquartzites of Pandukeshwar Formation of Vaikrata Group. Freezing and thawing due to snow and swelling action of rainwater had built up shearing stresses to a level that exceeded the shearing resistance of the slope, forming weathered metaquartzites along with interbedded sericite quartzite and a thin veneer of regolith along most vulnerable and weakest surface. Massive rockfall took place following increasant rains and cloud burst which widened the enlarged joints, particularly the joint pattern in the N45°E/80° SE direction including NE-SW trending bedrock. A number of trees and dead bodies were washed away due to the bursting of the debris dam across Malipa Gad and Kali...

011747   Nath T T (Regional Palaeontological lab, Geological Survey of India, Bandlaguda, Hyderabad-500 068) : Fresh water gastropods from the Maleri formation (upper triassic) of the Godavari valley, Andhra Pradesh. J Geol Soc India 1999, 54(4), 399-403.

Records the discovery of gastropods from the vertebrate fauna-bearing beds of Maleri Formation from southwest of Kataram in the Godavari valley. They include genera Physa, Lymnaea and Tricula which indicate a fresh water environment.

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011746   Maithy P K;Ghosh A K;Gopendra Kumar (NO, Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow-226 007) : First report of Dasycladacean alga - Cyclocrinites from the Ordovician of Takche formation, Spiti, India. J Geol Soc India 1999, 54(4), 379-85.

Deals with the first occurrence of cyclocrinitids, belonging to an extinct tribe of dasycladacean algae from the Ordovician of Takche Formation Spiti Valley, Himachal Pradesh, India. Cyclocrinites favus and Cyclocrinites pyriformis are described for the first time from the Ordovician of India and their stratigraphic significance and palaeoecological implications discussed.

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011745   Krishnamurthy P;Sarbajna C (Atomic Minerals Directorate for Exploration and Research, Department o, , Hyderabad-500 016) : Late archaean granitoid with a ring structure around Chandra, Mandya district, Karnataka. J Geol Soc India 1999, 54(4), 411-14.

Ring-like structure is defined by a late Archaean granite around Chandra. It is a fertile granite with a parental status akin to the rare metal pegmatite-hosted deposits of Li-Be-Nb and Ta around Allapatna-Marlagalla. This observation has important implications for new exploration targets for rare metal pegmatites in sourthern Karnataka and also geological evolution of the terrain as a whole.

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011744   Kotoky P;Baruah B;Borgohain R (NO, Regional Research Laboratory, Jorhat-785 006) : X-ray diffraction, infrared and isotope study of the Lakadong limestone, Meghalaya. J Geol Soc India 1999, 54(4), 421-30.

X-ray diffraction (XRD) and infrared (IR) spectral analyses of the Lakadong Limestone, Meghalaya indicate calcite as its dominant mineral phase. Association of dolomite at the base and presence of silica at the top of the sequence is evidence from the spectra. A significant relationship between CaO content and the peak intensity of IR-spectra is found and needs standardisation before it can be utilised for rapid estimation of quality of limestone and can be an alternative for different time consuming analytical procedures. Stable isotope of δ¹³C {0.63 to 1.12%(av. 0.87±0.01%)} points to enrichment of heavier C isotope and δ¹⁸O values {-7.34 to -10.55% (av.-9.06±0.01%)} to lighter O isotope enrichment. Isotopic grid analysis confirms the marine origin for the limestone. Biochemical fractionation along with diagenetic reorganisation might have played critical roles in controlling the isotopic ratios of this limestone.

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011743   Kalsi S R (NO, India Meteorological Department, Mausam Bhavan, Lodhi Road, New Delhi-110 003) : Multiple eyewall structure in an Arabian Sea cyclone. Curr Sci 1999, 77(9), 1175-80.

Depression was formed in the south-east Arabian Sea on the afternoon of 16 May 1999. While moving initially north-west and later northwards it rapidly developed through several stages on 17 May and acquired a wind speed more than 100 knots on 18 May. Multiple concentric and somewhat symmetric eyewalls were seen in this cyclone on 19 May 1999 when the intensification process had already stopped. Development and consequences of multiple eyewalls in this cyclone in terms of inner core intesification, outer core strengthening and recurvature are discussed.

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011742   Hanuma Prasad M;Hakim A;Krishna Rao B (NO, , GSI Colony, Sanjivani Nagar, Jabalpur-482 003) : Metavolcanic and metasedimentary inclusions in the Bundelkhand granitic complex in Tikamgarh district, Madhya Pradesh. J Geol Soc India 1999, 54(4), 359-68.

Bundelkhand Granitic Complex of central India contains inclusions of Archaean volcanic and sedimentary rocks and orthogneisses, some of which are 15 km by 6 km in size. Earlier workers considered that these inclusions belong to two distinct lithostratigraphic formations separated in time by a migmatization event. New data suggest that the migmatization event post-dated all of the volcanic and sedimentary rocks and hence the two-fold stratigraphic subdivision is not viable. Further, intrusion of orthogneisses resulted in an increase in grade of metamorphism in some volcanic and sedimentary rocks specifically near the contact.

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011741   Divya Prakash (Department of Geology, Banaras Hindu University, Varanasi-221 005) : Cordierite-bearing gneisses from Kodaikanal, South India : textural relationship and P-T conditions. J Geol Soc India 1999, 54(4), 347-58.

Kodaikanal is part of a Precambrian terrane characterized by granulite facies rocks. Cordierite-bearing gneisses here document spectacular reaction textures involving (Opx/Sp)-Cd symplectite and cordierite rim around resorbed garnet, consistent with the reactions : Garnet + Quartz = Orthopyroxene + Cordierite; Garnet + Sillimanite + Quartz = Cordierite; Garnet + Sillimanite = Spinel + Cordierite. Application of Gt-Bio, Gt-Opx, Gt-Cd and Sp-Cd thermometric, and Gt-Opx-Plag-Qtz, Gt-Sill-Plag-Qtz and Gt-Cd-Sill-Qtz barometric models to the granulite grade metapelites provides a P-T path which suggests that the rocks experienced substantial decompression (up to 3 kbar) and moderate cooling (150-200°C) subsequent to peak conditions of metamorphism ((c7.5 kbar, 750 ± 50°C). The polymetamorphic history of the study areas, interprekd from garnet consuming reaction textures and thermobarometric estimates, defines a decompressional P-T path followed by cooling of the rocks.

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