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Earthquakes are known to have occurred in Indian subcontinent from ancient times. This paper presents the results of seismic hazard analysis of India (6°-38°N and 68°-98°E) based on the deterministic approach using latest seismicity data (up to 2010). The hazard analysis was done using two different source models (linear sources and point sources) and 12 well recognized attenuation relations considering varied tectonic provinces in the region. The earthquake data obtained from different sources were homogenized and declustered and a total of 27,146 earthquakes of moment magnitude 4 and above were listed in the study area. The sesismotectonic map of the study area was prepared by considering the faults, lineaments and the shear zones which are associated with earthquakes of magnitude 4 and above. A new program was developed in MATLAB for smoothing of the point sources. For assessing the seismic hazard, the study area was divided into small grids of size 0.1° × 0.1° (approximately 10 × 10 km), and the hazard parameters were calculated at the center of each of these grid cells by considering all the seismic sources within a radius of 300 to 400 km. Rock level peak horizontal acceleration (PHA) and spectral accelerations for periods 0.1 and 1 s have been calculated for all the grid points with a deterministic approach using a code written in MATLAB. Epistemic uncertainty in hazard definition has been tackled within a logic-tree framework considering two types of sources and three attenuation models for each grid point. The hazard evaluation without logic tree approach also has been done for comparison of the results. The contour maps showing the spatial variation of hazard values are presented in the paper. [ABSTRACT FROM AUTHOR]

This paper reports the use of a GIS based Probabilistic Certainty Factor method to assess the geo-environmental factors that contribute to landslide susceptibility in Tevankarai Ar sub-watershed, Kodaikkanal. Landslide occurrences are a common phenomenon in the Tevankarai Ar sub-watershed, Kodaikkanal owing to rugged terrain at high altitude, high frequency of intense rainfall and rapidly expanding urban growth. The spatial database of the factors influencing landslides are compiled primarily from topographical maps, aerial photographs and satellite images. They are relief, slope, aspect, curvature, weathering, soil, land use, proximity to road and proximity to drainage. Certainty Factor Approach is used to study the interaction between the factors and the landslide, highlighting the importance of each factor in causing landslide. The results show that slope, aspect, soil and proximity to roads play important role in landslide susceptibility. The landslide susceptibility map is classified into five susceptible classes - low, very low, uncertain, high and very high − 93.32% of the study area falls under the stable category and 6.34% falls under the highly and very highly unstable category. The relative landslide density index (R index) is used to validate the landslide susceptibility map. R index increases with the increase in the susceptibility class. This shows that the factors selected for the study and susceptibility mapping using certainty factor are appropriate for the study area. Highly unstable zones show intense anthropogenic activities like high density settlement areas, and busy roads connecting the hill town and the plains. [ABSTRACT FROM AUTHOR]

Alaskan-type of plutonic complexes represent arc magma chambers and they occur throughout the earth's history from Archean to Phanerozoic periods around the globe. The ultramafic rocks from these complexes commonly contain spinels of varied chemistry, especially rich in Cr, Fe, and Ti coupled with low-Al contents when compared to the spinels from oceanic or continental rift domains. An attempt is made here to study Thenmudiyanur Mafic–Ultramafic Complex (TMUC) from the Belur Shear Zone (BLSZ) in the northeastern margin of Southern Granulite Terrane, located about 20 km SW of Tiruvannamalai Town. The important lithologies of TMUC include dunites, peridotites and pyroxenites surrounded by metagabbros and amphibolites. The dunites and peridotites are highly serpentinized with well-preserved cumulate olivines along with magnesite, chrome spinel and clinopyroxenes. The mineral chemistry of olivines represents higher forsterite (Fo88–90) and Mg# 87–90 [100×Mg/(Mg+Fe2+)] contents. The gradational contact within the rock types, compositional variations and cumulate nature of mineralogical characteristics suggest fractional crystallization of magma from a single parental source. The chrome spinels from these lithologies represent higher Cr# [100×Cr/(Cr+Al)] that ranges from 65 to 86 along with lower MgO (1.06–4.57 wt%) and MnO (<1 wt%) contents. The presence of chrome spinels together with olivine in dunites as well as peridotites and clinopyroxene mineral chemistry from pyroxenites reveal arc signatures for the evolution of TMUC, which seems to be similar to that of the Alaskan-type. Considering the tectonic setting and the age relationships of adjacent lithologies, it is opined that the TMUC might have evolved during the Neoproterozoic period. [ABSTRACT FROM AUTHOR]

Harvesting of water by tunnelling in the Western Ghats lateritic terrains of India known as surangam (tunnel well) is practiced since ages. It is common even today in the northern parts of Kerala state in India. Surangams are featured by horizontal tunnel wells, dug manually within the laterite, where the tunnel wall collects the seepage water, flows out under gravity and get accumulated in open tanks or dug wells for further use. The tunnels are laid horizontally or slightly inclined, placed just over the lithomarge clay so that maximum seepage can be accumulated through the porous laterites (generally of 3.95–30.20 m thick). A study is done on surangams from the Kasaragod district of Kerala, where it is still popularly used. They represent different designs; single tunnel, criss-cross tunnels and diversion tunnels, depending upon the terrain conditions, the permeability of the laterites and thickness of the saturated zones within laterites, demand of water and location of delivery points, etc. Surangam system may start from a dug well, end in a dug well and there can be an open shaft or dug well in between. Total 32 surangams are inventoried in Bedadka Panchayath, of which 24 are investigated in detail. The discharge varies from 0.078 to 13.29 m3/day during pre-monsoon while it remains between 172.80 and 691.20 m3/day during monsoon period in 2019. In 2019 summer, 12 inventoried surangams remained dry. The hydrochemical facies of water from the surangams generally varies from Ca–HCO3 type to Ca–Mg–Cl type indicating rock–water interaction. Because of lack of proper maintenance caving of walls occur during the rainy season. Lack of maintenance renders the priceless traditional groundwater abstraction structures disappearing fast. Surangams with good discharge are to be protected with proper concrete reinforcing of the outlet of the tunnel and proper storage options and arrangement of delivery systems up to the user point. Besides, water harvesting measures in the catchment of surangams are required for round the year sustainability of yield. A plan has been proposed for the revival of the surangams along with design specifications. [ABSTRACT FROM AUTHOR]

A comprehensive geophysical and petrological study was carried out at Giddalur area in Prakasam district, Andhra Pradesh, which is geologically a highly deformed area and is difficult to delineate the aquifer zone(s). The task was to find out the exact rock type in which aquifer is concealed as well as to delineate the aquifer zone, which can yield sufficient quantity of water. The resistivity models derived from geophysical dataset were interpreted in terms of hydrogeology and the results revealed substantial resistivity contrast of the geological formations within the study area. We have delineated two major groundwater potential zones based on this study. These zones were tapped at different depths in diverse rock types. Drilled hand specimens (rock cuttings) were not adequate, so these specimens were petrographically studied to reveal the exact contact zones of the rock type. On integration of the geophysical and the petrographic results, it was illustrated that two aquifer zones were struck at a depth of 92 and 122 m between shale-phyllite and phyllite-quartzite, respectively. These findings were correlated, which matched with the lithology of the drilled borehole. This integrated approach will be helpful in strategy for groundwater assessment as well as prospecting groundwater resources in different geological terrain. [ABSTRACT FROM AUTHOR]

An investigation has been carried out to identify the trends in maximum, minimum and mean temperatures and temperature range over the Indian land mass during the winter (January, and February), pre-monsoon (March-May), southwest monsoon (June-September) and post-monsoon (October-December) seasons by using high resolution daily gridded data set prepared by India Meteorological Department for the period of 1969-2005. It has been observed that the maximum temperatures over the west coast of India show rising trend in winter, southwest monsoon and post-monsoon seasons but the maximum temperatures do not show any significant trend over the other parts of the country. Minimum temperatures show increasing trend over the North Indian states in all seasons and they show an increasing trend over the west coast of India in winter and southwest monsoon seasons. Mean temperature shows an increasing trend over the west coast of India during winter and southwest monsoon seasons. Decreasing trend is observed in the temperature range over North India in all seasons due to increasing trend in minimum temperature. [ABSTRACT FROM AUTHOR]

The present study reports occurrence of helically coiled microfossil Obruchevella Reitlinger from the Owk Shale of the Kurnool Group from the peninsular India. The age of the Kurnool Group is poorly constrained due to the absence of direct radiometric dating and meager palaeobiological data. Occurrence of Obruchevella is considered as a typical Vendian marker genus recorded mostly from close to the Precambrian-Cambrian boundary successions. Hence, the present assemblage is important to ascertain the age of the basin. In the Owk Shale, four species of Obruchevella, viz., O. delicata, O. parva, O. minor and O. valdaica are recorded as organic walled microfossils. Among them O. valdaica is the largest in terms of size parameters. On the global scale, the recovered species occur in the Late Neoproterozoic to Early Cambrian sediments. Therefore, the occurrence of microfossil Obruchevella in the Owk Shale and known burrow structures in the Narji Limestone suggest Ediacaran age close to the Cambrian for the Kurnool Basin and challenges the recently assigned Mesoproterozoic age of the basin. [ABSTRACT FROM AUTHOR]

Two new palm leaf impressions, cf. Iguanura wallichiana and Palmacites makumensis sp. nov. are described from the Makum Coalfield, Tinsukia District, Assam. They belong to the Tikak Parbat Formation being considered as Late Oligocene (Chattian 28-23 Myr) in age. Their presence, along with the other known fossil records indicates that CMMT (cold month mean temperature) was not less than 18°C with plenty of rainfall, in the region during the period of deposition. [ABSTRACT FROM AUTHOR]

Pterospermumocarpon (Type: P. kalviwadiensis), a new morphogenus of fossil fruits showing resemblance with fruits of extant Pterospermum Schreb. (Malvaceae s.l.), is described from the Sindhudurg Formation (Miocene) at the Kalviwadi Village, Sindhudurg District, Maharashtra, India. Diagnostic feature of the fossil taxon is the dehiscent pentalocular capsule with five distinct sutures and imprints of winged seed-like structures in the locules. Recent modifications in the systematics of the Malvales, their fossil record, and the distribution and migration of Pterospermum and other malvalean taxa in the context of the Indian subcontinent are discussed. [ABSTRACT FROM AUTHOR]

A new fossil fruit wing of Shorea Roxb. belonging to the family Dipterocarpaceae is described from the Early Miocene sediments of Kachchh, Gujarat. It resembles best the extant species Shorea macroptera Dyer, which is a prominent member of the tropical evergreen forests of the Malayan Peninsula. The present finding, along with the other megafossil records described from the same area, indicates a typical tropical vegetation with a warm and humid climate at the time of deposition in contrast to the present day xeric vegetation in the area. As the family Dipterocarpaceae no longer exists in western India, it is essential to discuss the time of its extinction and possible causes, which may include drastic changes in the climate of the region. The present finding also supports the theory of a Malaysian origin for the family in contrast to the hypothesis of a Gondwanan origin. [ABSTRACT FROM AUTHOR]

Tephra, emplaced as a result of Pleistocene eruption of the Indonesian 'supervolcano' Toba, occurs at many localities in India. However, the ages of these deposits have hitherto been contentious; some workers have argued that these deposits mark the most recent eruption (eruption A, ca 75 ka), although at some sites they are stratigraphically associated with Acheulian (Lower Palaeolithic) artefacts. Careful examination of the geochemical composition of the tephras, which are composed predominantly of shards of rhyolitic glass, indicates that discrimination between the products of eruption A and eruption D (ca 790 ka) of Toba is difficult. Nonetheless, this comparison favours eruption D as the source of the tephra deposits at some sites in India, supporting the long-held view that the Lower Palaeolithic of India spans the late Early Pleistocene. In principle, these tephra deposits should be dateable using the K-Ar system; however, previous experience indicates contamination by a small proportion of ancient material, resulting in apparent ages that exceed the true ages of the tephras. We have established the optimum size-fraction in which the material from Toba is concentrated, 53-61 μm, and have considered possible origins for the observed contamination. We also demonstrate that Ar-Ar analysis of four out of five of our samples has yielded material with an apparent age similar to that expected for eruption D. These numerical ages, of 809 ± 51, 714 ± 62, 797 ± 45 and 827 ± 39 ka for the tephras at Morgaon, Bori, Gandhigram and Simbhora, provide a weighted mean age for this eruption of 799 ± 24 ka (plus-or-minus two standard deviations). However, these numerical ages are each derived from no more than 10-20% of the argon release in each sample, which is not ideal. Nonetheless, our results demonstrate that it is feasible, in principle, to date this difficult material using the Ar-Ar technique; future follow-up studies will therefore be able to refine our preparation and analysis procedures to better optimize the dating. [ABSTRACT FROM AUTHOR]

The Jaduguda U (-Cu-Fe) deposit in the Singhbhum shear zone has been the most productive uranium deposit in India. Pyrite occurs as disseminated grains or in sulphide stringers and veins in the ore zone. Veins, both concordant and discordant to the pervasive foliation, are mineralogically either simple comprising pyrite ± chalcopyrite or complex comprising pyrite + chalcopyrite + pentlandite + millerite. Nickel-sulphide minerals, though fairly common in concordant veins, are very rare in the discordant veins. Pyrite in Ni-sulphide association is commonly replaced by pentlandite at the grain boundary or along micro-cracks. Based on concentrations of Co and Ni, pyrite is classified as: type-A - high Co (up to 30800 ppm), no/low Ni; type-B - moderate Co (up to 16500 ppm) and moderate to high Ni (up to 32700 ppm); type-C - no/low Co and high Ni (up to 43000 ppm); type-D - neither Co nor Ni. Textural and compositional data of pyrites suggest that the hydrothermal fluid responsible for pre-/early-shearing mineralization evolved from Co-rich to Ni-rich and the late-/post-shearing fluid was largely depleted in minor elements. Sulphur isotope compositions of pyrite mostly furnish positive values ranging between −0.33 and 12.06‰. Composite samples of pyrites with only type-A compositions and mixed samples of type-A and type-B are consistently positive. However, pyrite with mixed type-A and type-C and pyrite with type-D compositions have negative values but close to 0‰. By integrating minor element and sulphur isotope compositions of pyrite in conjunction with other published data on the Jaduguda deposit, it is proposed that reduced sulphur for the precipitation of most pyrites (type-A, type-B) was likely derived from isotopically heavy modified seawater. However, some later sulphur might be magmatic in origin remobilized from existing sulphides in the mafic volcanic rocks in the shear zone. [ABSTRACT FROM AUTHOR]

Composition of chromiferous spinel included in olivines of Mg-rich basalts and gabbros of the Deccan Traps (Gujarat and Western Ghats) are reported here. They vary from Al-rich compositions [AlO = 53wt.%; Cr#, 100Cr/(Cr + Al) = 12] to Cr-rich compositions [CrO = 51wt.%; Cr# = 84], and from Cr-Al rich compositions towards Cr-rich Ti-magnetite (TiO up to 23 wt.%, ulvöspinel up to 67mol.%). The Mg# [100Mg/(Mg + Fe)] of spinel decreases from 81 to nearly zero. The highest Cr# has been found in the Bushe Fm., Thakurvadi Fm., and some high-Ti basalts of the Pavagadh section, whereas some of the low-Ti basalts of Saurashtra have Al-rich compositions typical of spinels found in mid-ocean ridge basalts. The chemical composition of the Deccan Trap spinels is completely different compared to that observed in mantle spinel suites, with very few exceptions. The decreasing Al and increasing Fe and Ti of spinel seems to be mainly the result of decrease of Mg in the locally coexisting melts and favourable cationic substitutions in the lattice. There is barely any evidence of general relationships between the composition of the Deccan spinels and inferred mantle sources of the host magmas. Pyroxene inclusions in spinels may witness a high-pressure stage of crystallization, but the possibility of non-equilibrium crystallization, or even magma mixing, cannot be ruled out. Overall, the compositional ranges of chromiferous spinel in the Deccan Traps closely match those observed in the other Large Igneous Provinces having mafic/ultramafic intrusions and mafic magma compositions (e.g., Siberian Traps, Karoo, Emeishan). [ABSTRACT FROM AUTHOR]

The geological complexities of banded iron formation (BIF) and associated iron ores of Jilling-Langalata iron ore deposits, Singhbhum-North Orissa Craton, belonging to Iron Ore Group (IOG) eastern India have been studied in detail along with the geochemical evaluation of different iron ores. The geochemical and mineralogical characterization suggests that the massive, hard laminated, soft laminated ore and blue dust had a genetic lineage from BIFs aided with certain input from hydrothermal activity. The PAAS normalized REE pattern of Jilling BIF striking positive Eu anomaly, resembling those of modern hydrothermal solutions from mid-oceanic ridge (MOR). Major part of the iron could have been added to the bottom sea water by hydrothermal solutions derived from hydrothermally active anoxic marine environments. The ubiquitous presence of intercalated tuffaceous shales indicates the volcanic signature in BIF. Mineralogical studies reveal that magnetite was the principal iron oxide mineral, whose depositional history is preserved in BHJ, where it remains in the form of martite and the platy hematite is mainly the product of martite. The different types of iron ores are intricately related with the BHJ. Removal of silica from BIF and successive precipitation of iron by hydrothermal fluids of possible meteoric origin resulted in the formation of martite-goethite ore. The hard laminated ore has been formed in the second phase of supergene processes, where the deep burial upgrades the hydrous iron oxides to hematite. The massive ore is syngenetic in origin with BHJ. Soft laminated ores and biscuity ores were formed where further precipitation of iron was partial or absent. [ABSTRACT FROM AUTHOR]

A group of 36 coral islands is being scattered in the Arabian Sea off the western coast of India. On such islands, groundwater is the only source of fresh water for the islanders. The demand for groundwater is increasing every year due to growing population and urbanization. On the other side the peculiar hydrologic, geologic and geomorphic features restrict the availability of groundwater. Thus a proper understanding of the groundwater condition is important in order to meet this increasing demand and also to formulate future development and management strategies. Detailed hydrogeological, geophysical and hydrochemical studies had been carried out to identify potential fresh groundwater resources and quantify vulnerable parts of Andrott Island, Union Territory of Lakshadweep. Systematic collection and analysis of hydrological, geophysical and hydrochemical data gives an early signal of deterioration in groundwater quality in the peripheral parts of eastern and western coasts of this island and it suggests immediate measures for arresting the deterioration in groundwater quality as well as augmentation for restoration of aquifer in some parts of the island. [ABSTRACT FROM AUTHOR]

Cretaceous phosphorites from the onshore of Tamil Nadu have been investigated for their origin and compared with those in the offshore. Cretaceous phosphorites occur as light brown to yellowish brown or white nodules in Karai Shale of the Uttatur Group in the onshore Cauvery basin. Nodules exhibit phosphatic nucleus encrusted by a chalky shell of carbonate. The nucleus of the nodules consists of light and dark coloured laminae, phosphate peloids/coated grains and detrital particles interspersed between the laminae. Scanning electron microscope (SEM) studies reveal trapping and binding activity of microbial filaments. A mat structure with linearly arranged microbial filaments and hollow, cell-based coccoid cyanobacterial mat are present. Nodules contain abundant carbonate fluorapatite, followed by minor calcite, quartz and feldspar. The P2O5 content of the phosphorites ranges from 18 to 26%. The CaO/P2O5, Sr and F contents are higher than that of pure carbonate fluorapatite. Concentrations of Si, Al, K, Fe, and Ti are low. We suggest that the nuclei of the nodules represent phosphate clasts related to phosphate stromatolites formed at intertidal conditions. At high energy levels the microbial mats were disintegrated into phosphate clasts, coated with carbonate and then reworked into Karai Shale. On the other hand, Quaternary phosphorites occur as irregular to rounded, grey coloured phosphate clasts at water depths between 180 and 320m on the continental shelf of Tamil Nadu. They exhibit grain-supported texture. Despite Quaternary in age, they also resemble phosphate stromatolites of intertidal origin and reworked as phosphate clasts onto the shelf margin depressions. Benthic microbial mats probably supplied high phosphorus to the sediments. Availability of excess phosphorus seems to be a pre-requisite for the formation of phosphate stromatolites. [ABSTRACT FROM AUTHOR]

We present five new discriminant function diagrams based on an extensive database representative of basic and ultrabasic rocks from four tectonic settings of island arc, continental rift, ocean-island, and mid-ocean ridge. These diagrams were obtained after loge-transformation of concentration ratios of major-elements -- a technique recommended for a correct statistical treatment of compositional data. Higher % success rates (overall values from ∼83 to 97%) were obtained for proposing these new diagrams as compared to those (∼82 to 94%) obtained from the discriminant analysis of the raw major-element concentration data (i.e., without the loge-transformation and without taking ratios of the compositional data, but using exactly the same database to provide an unbiased comparison), suggesting that such a data transformation constitutes a statistically correct and recommended technique. The new diagrams also resulted in less mis-classification of basic and ultrabasic rocks from known tectonic settings than the diagrams obtained from the raw data. The use of these highly successful new discriminant function diagrams is illustrated using Miocene to Recent basic and ultrabasic rocks from three areas of Mexico with complex or controversial tectonic settings (Mexican Volcanic Belt, Los Tuxtlas volcanic field, and Eastern Alkaline Province), as well as older rocks from three areas (Deccan, Malani, and Bastar) of India. Additionally, the major-element data from two 'known' continental arc settings are used to show that they are similar to those from the island arc setting. Continental rift setting is inferred for all Mexican cases and for one cratonic area of India (Malani) and an IAB setting for the Bastar craton. The Deccan flood basalt province of India is used to warn against an indiscriminate use of those discrimination diagrams that do not explicitly include the likely setting of the area under evaluation. An Excel template is also provided for an easy application of these new diagrams for discriminating the four settings considered in this work. [ABSTRACT FROM AUTHOR]

This study uses 1 yr of eddy covariance (EC) flux observations to investigate seasonal variations in evapotranspiration (ET) and surface energy budget (SEB) closure at a tropical semi-deciduous forest located in north-east India. The annual cycle is divided into four seasons, namely, pre-monsoon, monsoon, post-monsoon and winter. The highest energy balance closure (76%) is observed during pre-monsoon, whereas the lowest level of closure (62%) is observed during winter. Intermediate closure of 68% and 72% is observed during the monsoon and post-monsoon seasons, respectively. Maximum latent heat flux during winter ( 150 W m - 2 ) is half of the maximum latent heat ( 300 W m - 2 ) flux during the monsoon. ET is a controlling factor of SEB closure, with the highest rates of closure corresponding to the periods of the highest ET. The Bowen ratio ranges from 0.93 in winter to 0.27 during the monsoon. This is the first time the role of ET in the seasonal variation of SEB closure has been reported for any ecosystem in north-east India using EC measurements. [ABSTRACT FROM AUTHOR]

The influence of local meteorology and convection activities on the vertical distribution of carbon monoxide (CO) over Chennai in southern India was investigated by analysing the measurements of ozone aboard airbus in-service aircraft observations during the years 2012–2013. The seasonal variation of CO in the free troposphere was observed to be different and less pronounced than that in the planetary boundary layer (PBL). The near surface mixing ratio of CO was the highest ( 190 ± 68 ppbv ) during winter, while enhanced values ( 117 ± 11 ppbv ) in the free troposphere were observed during post-monsoon. The mixing ratios were the lowest throughout the troposphere during the monsoon. In the PBL, the mixing ratios of CO showed a decline with an increase in wind speed and were the highest ( > 200 ppbv ) under stagnant conditions ( 1 - 2 m s - 1 ) during winter. The higher CO in the lower free troposphere during the pre-monsoon period is attributed to the stronger biomass burning emissions. In the middle–upper troposphere, higher levels of CO during post-monsoon are due to the enhanced vertical mixing of regional emissions associated with weaker wind shears and frequent convection activities. Overall, the contrasting effects of stronger CO emissions can be observed in winter/pre-monsoon, while the efficient vertical mixing during the monsoon/post-monsoon season governs the observed seasonality of CO. The model for ozone and related chemical tracers, version 4 (MOZART-4) provides a reasonable representation of the convection effect on the CO mixing ratio. This study highlights a need to conduct more observations, especially of aircraft-borne instruments, to understand the effects of regional-scale emissions and dynamics in the middle–upper tropospheric chemistry over South Asia. [ABSTRACT FROM AUTHOR]

Amphibolites and Abukuma-type low-grade and low-pressure meta-sedimentary rocks (MSR) host mineralised rare metal (Nb-Ta, Be and Li)- and Sn-bearing granite pegmatites and their parental, fertile S-type granites in the Bastar-Malkangiri Pegmatite Belt (BMPB) in the SE part of the Bastar craton in parts of Chhattisgarh and Odisha, India. Amphibolites, based on their field relationship (as sills in MSR), mineral assemblage and textural features, are broadly classified into three types: (i) tremolite-, (ii) hornblende-actinolite-, and (iii) hornblende-bearing amphibolites. Petrochemically, amphibolite types (i-iii) show a regular decrease in their Mg content and related trace elements such as Cr (81-1731 ppm), Ni (135-379 ppm) and Co (23-68 ppm) and, hence, are designated, respectively, as high-, intermediate- and low-Mg amphibolites. All the three types show slight enrichment in Si, Fe and P, reflected in their normative quartz, hypersthene and lesser diopside, magnetite, ilmenite and apatite, but no olivine. They are relatively enriched in incompatible elements such as Rb (16-526 ppm), Ba (15-538 ppm), Zr (56-147 ppm) and Nb (3-44 ppm), with relatively a higher concentration of these elements in those near to the contacts with pegmatites, thereby demonstrating some influence of the pegmatites on the chemistry of the host amphibolites. In spite of these, the three types of amphibolites show regular differentiation trends, reflected by their systematic decrease of Ni, Cr and Co with a decrease of Mg, and also show Fe-enrichment in their alkalies (Na2O+K2O)-(FeO+Fe2O3)-MgO (AFM) plot. The field, petrography and major-minor trace elements petrochemistry, including rare earth elements with slight negative to no Eu-anomaly, and their chemical patterns cumulatively point out that these amphibolites are ortho-type and sub-alkaline in nature, with quartz tholeiitic magmatic affinity, and the formation due to more of fractional crystallisation and less of 5-25% partial melting of an enriched primordial mantle magma (enriched mid-oceanic ridge basalt - E-MORB), emplaced at a deduced shallow depth of 10-25 km, with the main controlling phases being olivine, plagioclase, clinopyroxene and apatite. [ABSTRACT FROM AUTHOR]

The Kaladgi Basin on the northern edge of the Dharwar craton has characters diverse from the other epicratonic Purana basins of Peninsular India. Sedimentological studies in the basin have established the presence of three cycles of flooding separated by an event of intra-basinal deformation accompanied by low grade incipient metamorphism. The overall structural configuration of the basin indicates its development by supracrustal extension accompanied by shearing in a trans-tensional regime during the Mesoproterozoic. This was followed by sagging that yielded Neoproterozoic sedimentation in a successor nested basin. 40Ar/39Ar dating of an intrusive mafic dyke along the axial plane of a fold has yielded a plateau age of 1154±4Ma. This helps constraint the age of the various events during the evolution of this basin. [ABSTRACT FROM AUTHOR]