Showing papers in "Journal of Geological Society of India in 2000"

Tectonothermal History of the Central Indian Tectonic Zone and Reactivation of Major FauIts/Shear Zones

Abstract: Central Indian Tectonic Zone (CITZ), which divides the Indian subcontinent into Bundelkhand Block in the north and the Deccan Block in the south, is represented by a collage of different lithotectonic terranes ranging in age from Archaean to Recent. It comprises two parallel structural domains, namely the Son-Narmada (SONA) subzone in the north and the Sausar mobile belt (SMB) in the south. The ancestry of the SONA subzone is indicated by the Neoarchaean - Palaeoproterozoic ages yielded by the rocks of Mahakoshal fold belt; the Sausar belt, on the other hand, has yielded Meso- to Neo-proterozoic ages. The present response of CITZ to accumulation of stress and attendant seismicity is governed by the structures generated due to early tectonic history of rocks within it, particularly the development of number of E-W to ENE-WSW striking, brittle and ductile shear zones. While the Sausar belt has remained more or less stable since the late Precambrian, the SONA and Tapti lineament zones have been reactivated several times. Two prominent ENE-WSW trending deep fautts, termed the Son-Narmada North Fault (SNNF) and Son-Narmada South Fault (SNSF) have been episodically active from Neoarchaean onwards. The SNSF in particular has witnessed protracted reactivation well into the Phanerozoic. Intraplate seismicity in continents is commonly concentrated along ancient fault zones. Reactivation of faults or shear zones is favoured over new fault generation, since the SNSF is in a high shear stress orientation. Although the Sausar mobile belt is marked by a number of E-W trending parallel ductile shears, mass transfer processes such as silicification, recrystallization and grain growth during Precambrian appear to have healed them.

Hydrochemistry and Quality Assessment of Groundwater in Naini Industrial Area, Allahabad District, Uttar Pradesh

Abstract: The chemical characteristics of groundwater in and around the industrial area of Naini district, Allahabad have been studied to evaluate the suitability of water for irrigation and domestic uses. Sixty five water samples representing the shallow and deep groundwater of the area were collected and analysed for pH, EC, TDS, HCO 3 , CO 3 , SO 4 , Cl, Ca, Mg, Na and K. It is observed that the quality of the groundwater is suitable for domestic use with some exception. The observed high quantity of heavy metals at some sites requires immediate attention and detailed study. The calculated values of SAR, RSC and sodium percentage indicate the good to permissible quality of water. However, the high sodium percentage and RSC values at certain sites restrict its suitability for agricultural purposes.

Rapid Development of the Late Archaean Hutti Schist Belt, Northern Karnataka: Implications of New Field Data and SHRIMP U/Pb Zircon Ages

Abstract: The Palkanmardi conglomerate is one of many polymict conglomerates interbedded with greywackes in the NE of the Hutti schist belt. These conglomerates are up to a few metres thick, unsorted and include rounded to sub-angular clasts of granodiorite, granite, vein quartz and rnetabasalt in a matrix of coarse-to medium-grained greywacke. Cross-bedding, convolute bedding and grading are well preserved in the interbedded greywackes in spite of deformation and homfelsing during Late Archaean regional high temperature - low pressure metamorphism. These primary structures and lack of sorting in the conglomerates are consistent with deposition as turbidites and debrites in an unstable submarine environment. This new interpretation contrasts with previous views that the Palkanmardi conglomerate is autoclastic, pyroclastic-detrital or glacio-fluvial. The conglomerate-greywacke sequence occurs low in the lithostratigraphy and is overlain by metabsalts. A clast of granodiorite in the conglomerate bed at Palkanmardi village has yielded a SHRIMP weighted mean 207 Pb/ 206 Pb zircon age of 2576±12 Ma which is interpreted as the magmatic age of the erosional provenance. Moreover, SHRIMP zircon geochronology using a sample from the steep elongate wedge of granodiorite that extends for at least 150 km SE of the schist belt has yielded a weighted mean 207 Pb/ 206 Pb age of 2561±24 Ma and a concordia upper intercept age of 2580±31 Ma. These ages are indistinguishable within their errors and are interpreted as the age of magmatic crystallisation. Combined with the low stratigraphic position of the Palkanmardi conglomerate, the age data imply that basin development (volcanism and sedimentation) in the Hutti belt was not only rapid, but began very late in the Archaean history of this part of the Dharwar craton.

Crustal Velocity Structure of the Dharwar Craton, India

Abstract: Re-examination of analog seismic data acquired across Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC) (western and middle parts of Kavali-Udipi DSS profile) indicate significant velocity variations in WDC and EDC. The synthesis of velocity details with the available geological signatures suggests that the two segments of the Dhanvar Craton have varying structure and evolution.

The Radial and Linear Modes of Interaction between Mantle Plume and Continental Lithosphere: A Case Study from Western India

Abstract: The study examines the interaction between continental lithosphere (CL) and deep mantle plume. For this purpose, the Indian CL and the Reunion plume have been considered, with special emphasis on the consequent development of geophysical, tectonic and structural features. It reveals a bimodal pattern (linear and radial) of these manifestations. The radial one is correlated with the outburst of the plume-head, while the pre- and post-outburst phases follow a linear mode due to the traverse of Indian plate over the plume. It is seen that, the plume-CL interaction is facilitated by mobile belts and resisted by cratons.

Rupture Mechanism of Chamoli Earthquake on 29 March 1999 and its Implications for Seismotectonics of Garhwal Himalaya

Abstract: Chamoli earthquake of 29 March, 1999 (m b 6.8) has caused extensive damage to life and property. Macroseismic surveys conducted around Chamoli have indicated maximum intensity of VIII on MSK scale. The epicentral tract of this event is oriented in the E-W direction. The aftershocks for the first few days are concentrated in an area of 40 km x 30 km which is bound by MCT in the north and the Alkananda Fault in the south. The authors have suggested a source model of this event on the basis of data generated as well as the seismotectonic setting of the area and have surmised that this event nucleated at the intersection of a transverse fault and the rupture propagated towards west along the detachment surface.

Trace Fossils from the Pin Section of Spiti Valley, Himachal Pradesh and their Stratigraphic Significance

Abstract: The Early Cambrian trace fossils Planolites, Skulithos, Psammichnites, Neonereites, Didymaulichnus, Monurnorphichnus, Dirnorphichnus, Diplichnites, Rusophycus and Cruzianu are described from the Kunzum La Formation (Haimanta Group) of the Pin section in Spiti valley. These trace fossils occur well below the body fossil zone reflecting their abundance at two stratigraphic levels. The Precambrian-Cambrian boundary could be well betow the earliest trace fossil horizon. The abundance of trace fossils at these two levels is a universd phenomenon in the Himalaya and indicates two acme zones with proliferation of vermiform organisms in the lower zone and arthropod forms in the upper zone.

Evidence of a Palaeoseismic Event from the Deccan Plateau Uplands

Abstract: Palaeoseismic evidence is recorded for the first time from the upland region near the crest of the Deccan plateau. Some of the soft-sediment deformation structures from Quaternary sediments in the Chandanapuri valley are interpreted as seismites. These sediments rest nonconformably upon the Deccan Traps and are inherently anomalous vis-a-vis their location in the river valley. Based on various features and their position in the succession of the sediments, these seismites are provisionally attributed to a single event with an inferred magnitude > 6.5 M, which occurred 5000 - 7000 years ago. This report highlights the need to re-evaluate the traditional perception of the aseismic nature of the main Deccan plateau.

Problems of Classifying Early Oligocene Reticulate Nummulites (Foraminiferida) from Southwestern Kutch, Gujarat

Abstract: Problems of classifying the A and B Forms of reticulate Nummulites with large embryonic apparatus and intercalary whorls respectively from Early Oligocene rocks of Maniyara Fort Formation, south-western Kutch are discussed. The taxon is described and illustrated; pending further investigations, it is provisionally identified here as Nummulites cf. fichteli Michelloti.

Evidences for Soda Metasomatism in Ladera-Sakhun Area, Northeastern Rajasthan

Abstract: Albitite and albitised banded gneissic country rock from the Ladera-Sakhun area, situated about 80km southwest of Jaipur, show several evidences for soda metasomatism. Megascopic evidences include reddening of outcrops due to aventurisation, gradational contacts between albitite and gneisses, development of metasomatic minerals, dequartzification, epidotization and cataclasitisation. Microscopic evidences include relict microcline in the newly formed albite grain, poor and discontinuous development of twin lamellae in albite giving step-like appearance, ubiquitous sweeping extinction in albite due to cataclasitisation, occasional mortar texture in albitite, tapering of twin lamellae within the grain, twin lamellae forming in chequered fashion, development of aventurine albite containing dusty Fe-oxide inclusions, development of albite along twin/cfeavage plane of microcline, formation of new albite in plagioclase, destruction of sericite in plagioclase of albitised granite, formation of myrmekite of intergranular, intragranular and rim types, development of epidote corona around clinopyroxene in pyroxenite, partial to complete dequartzification and filling up of voids by calcite. Petrochemical evidences of increased characteristic values of Na 2 O from 3.17 to 7.00 wt%, K 2 O and Si 2 O from -0.03 to -6.00 wt% and -0.76 to -10.55 wt% in the unalbitised to albitised rocks respectively, provide further support for soda metasomatism. Albitisation at Ladera-Sakhun area extends over a considerable distance into Haryana in the NE and beyond Tal in the SW, attesting to its regional significance and its potential for mineralisation.

"Possible Microfossils" from the Archaean Banded Iron Formation (Bailadila Group), Madhya Pradesh, India

Abstract: SEM studies have recorded presence of filamentous and unicellular spheroidal structures which are regarded as "possible microfossils", from the stromatolitic Archaean (ca. 3.0 Ga old) banded iron formation (BIF), Bailadila Group. Spheroidal bodies have diameters that range from 0.5 to 6.9 microns. The frequency of forms with smaller diameters is greater than those with the diameter above 3.0μm. The filamentous structures range from less than 100 nanometres to 1.2μm in diameter. Syngenetic nature of these microfossils has been established. Though a large number of these microfossils could be identified in the SEM, they could not be observed in petrographic thin sections under optical microscope most probably because of their association with, and being clouded by, opaque haematite.

Petrology of the Dykes of Ravipadu, Prakasam Province, Andhra Pradesh, India

Abstract: The doleritic and basaltic dykes of Ravipadu in the Prakasain Province traverse and extend beyond the gabbro pluton. The dolerites exhibit ophitic - subophitic, intergranular and equigranular textures. The basaltic dykes include lamprophyres (camptonites) and porphyritic basaltic dykes which display porphyritic/glomeroporphyritic and panidiomorphic textures. The chief rock forming minerals in these dykes are olivine, clinopyroxene and plagioclase with subordinate orthopyroxene, amphibole and biotite. The accessory minerals include opaques and green spinel. The dolerites and basaltic dykes show contrasting major dement compositions, especially with respect to alkalies and alkali/silica ratios, normative mineralogy and rare earth element concentrations and patterns. The dolerites, which contain modal and normative hypersthene, are tholeiitic and show iron enrichment as the differentiation proceeds. They show LREE enriched and HREE depleted patterns with positive Eu anomalies. Basaltic dykes in which modal and normative hypersthene is conspicuously absent are calc-alkaline to alkaline and are LREE enriched without any perceptible Eu anomalies. Petrogenetic modelIing suggests that the dolerites are probably replenished liquids which are geochemically similar to the parental magmas of the host gabbros, whereas the basaltic dykes are genetically unrelated to the dolerite dykes and to the host gabbros. The basaltic dykes are believed to have formed from the melts of an LREE enriched mantle and are emplaced in a rift setting, during an extensional regime.

Verdine and Glaucony Facies from Continental Margin Off Chennai, Bay of Bengal

Abstract: Green and brownish green grains associated with surficial sediments of outer continental shelf and subsurface sediments of upper slope off Chennai have been investigated for their distribution. The green and brownish grains account for 40% of the sediments in the outer continental shelf while in the upper slope the green grains account for 20-90% of the sediments. X-ray diffractograrns reveal that the grains from outer shelf are mainly composed of Phyllite V clay mineral of the verdine facies and a mixture of detrital clays. The grains from the upper slope constitute glauconitic slnectite and glauconitic mica of the glaucony facies. The ferric oxide and potassium oxide contents of the grains confirm their verdine and glaucony facies respectively. Their distribution pattern signifies the palaeobathymetric and palaeoenvironmental conditions of the area. Glaucony facies in upper continental slope apparently belong to the period of Last Glacial Maximum (LGM) and verdine facies in outer continental shelf to subsequent transgression.

Mineralogical and Chemical Characteristics of Complexly-Zoned Columbite-Tantalite from the Rare Metal Pegmatites of Southern Karnataka

Abstract: Detailed mineralogical and chemical studies by EPMA on the Nb-Ta minerals from the rare metal pegmatites of southern Karnataka have revealed wide compositional variations, and the presence of some new minerals like tapiolite and microlite, hitherto unreported from these pegmatites. Back scattered electron (BSE) images have indicated complex zoning patterns such as oscillatory, patchy and/or their combinations, associated with replacement of columbite-tantalite by microlite, manifested by the variations of Nb 2 O 5 , Ta 2 O 5 , FeO and MnO. Such features, although known from a few rare meral pegmatites of the world, are being recorded here for the first time in India. Oscillatory zones in columbite-tantalites are manifested as alternating dark and light grey coloured bands, of which darker bands are Nb-rich (30-300 μM thick) and lighter bands are Ta-rich (125-450 μm thick). The wider zones may, in turn, consist of a group of very fine sub-zones (1-50 μm) of slightly varying composition: Patchy zoned crystals exhibit corroded remnants of early formed columbite-tantalite (with 39.73-44.02% Ta 2 O 5 ), surrounded by later formed zones which are enriched in Ta 2 O 5 (up to 50.99 %) in columbite-tantalite leading to the formation of microlite containing up to 73.4% Ta 2 O 5 . The zoning of the columbite-tantalites has been attributed to periodic changes in the composition of the major components such as Nb, Ta, Fe and Mn in the pegmatite fluid system, apparently influenced by the late stage fractionation of volatiles. This ultimately generated fluids rich in Ta and Na, resulting in resorption and replacement with patchy zoning of early formed, zoned columbite-tantalites.

A Statistical Analysis of Completeness of Earthquake Data of Peninsular India and its Implications for Seismicity Evaluation

Abstract: The best available data from different compilations have been consolidated and homogenised for the Indian peninsular shield These historical and instrumental data of 410 years (1586 - 1995) have been subjected to statistical completeness test to determine time - intervals in which the data sets are complete in different ranges (classes) of magnitude The analysis reveals that the data are complete for the last about 40 years, 60 years and 120 years from present in the magnitude cIasses 40≤M<50, 50≤M<60 and M≥60 respectively The two significant parametric constants of seismicity (a and b values) obtained by regression analysis of these data sets turn out to be 459 and 094 respectively that are typically indicative of a moderately active zone such as the continental interior of southern India is indeed so Based on this deduction, the recurrence time-interval for a Latur type earthquake (M 63) in the Indian shield region works out to be close to 215 years The magnitude of Design Basis Earthquake (DBE), assumed to occur not more than once in 50 years in the peninsular shield region, works out to be close to 67

Simulation of Arid Multi-Layer Aquifer System to Evolve Optimal Management Schemes: A Case Study in Shashe River Valley, Okavango Delta, Botswana

Abstract: A multi-leaky aquifer system in Shashe river valley (Okavango delta), Botswana was simulated to study the aquifer response and thereby evolve optimal pumping schemes. The river valley falls in an arid region and has three aquifers separated by two aquitards. The upper alluvial aquifer below the narrow riverbed is being exploited to augment drinking water supply to the nearby wildlife tourist center, Maun. The bottom aquifer is saline. Continuous increase of abstraction from the upper unconfined and middle semi-confined aquifers has been causing progressive decline of water levels in these aquifers, as well as migration of saline water to the middle aquifer. In order to quantify the upward flow from the saline unit, a multi-layer model was constructed and calibrated for both steady state and transient condition. The calibration was reasonably good even with the given limited water level history for the middle (semi-confined) aquifer system. The calibration has shown that vertical conductivity (K 1 ) of the confining layers has a considerable influence on the hydrodynamics of multi-aquifer system. As a natural corollary, groundwater movement to the middle (semi-confined) aquifer is found to be dependent on the vertical downward leakage from the upper phreatic aquifer and upward leakage from the lowermost saline unit. As the river-derived recharge to the phreatic aquifer has been negligible due to no-flow condition existing in the riverbed for nearly a decade, even a moderate pumping rate of 3150m 3 /day may cause severe damage to the middle aquifer. The upper reaches of the middle semi-confined aquifer are likely to become unconfined and the upward leakage from the underlying saline aquifer will increase the concentration of total dissolved solids (TDS). The situation may be improved by reconfiguration of well fields. The longevity of wellfields will increase if the pumping rate from the lower reach is reduced and that from middle and upper reaches is increased.

Gold and PGM Contents in a Subvolcanic Deccan Picrite of Saurashtra, Gujarat

Abstract: Some samples from a chrome spinel-bearing intrusive picrite within olivine rich Deccan basalts at Limbdi in Saurashtra show anomalous high contents of gold (148-231 ppb), platinum (15-125 ppb) and palladium (17-311 ppb). Other samples bear an avenge of ∼6 ppb of gold, ∼31 ppb of platinum and ∼42 ppb of palladium. Sulphide mineralisation in the picrite is of extremely fine grain size, with low to moderate whole-rock contents of sulphur varying between 0.08 to 0.53 %. Higher values of gold and platinum are found in the western olivine-rich portion of the intrusive, while at surface level platinum/palladium ratio decreases due east with increase in palladium. This intrusive with higher average contents of precious metals could be a potentid target for exploration. Such high contents of gold, platinum and palladium are hitherto unreported from Deccan volcanic province.

Ancient Denudational Surfaces in the Gondwana Sequences of Peninsular India

Abstract: Gondwana basins of Peninsular India contain a thick pile of clastic sediments of predominantly fluvial origin. As expected in such a depositional milieu, the sedimentary pile is punctuated by numerous episodes of contemporaneous uplift, non-deposition and erosion. Most of these events are localised in nature and hence not correlatable from one basin to another. However, a few events of regional nature can be recognized. They comprise (a) basement surface with glaciated features like polishing, striations and frost wedging below the basal Talchir strata; (b) surface of angular and erosional unconformity between Permian/Triassic and Early Triassic/infra - Late Norian and (c) a major diastrophic episode resulting in reversal of palaeoslope between Late Jurassic and Early Cretaceous. Besides these, localized events represented by surfaces of contemporaneous subaerial exposure and oxidation showing characters of pedogenic (palaeosol) and lateritic (latosol) profiles have been recorded. These include Lower Barakar (Early Permian) of Hutar basin of Koel valley, Barren Measures (Late Permian) and Triassic/Jurassic contact of Rewa and Satpura basins, and Late Cretaceous Lometa Beds in Rewa Basin. Breaks represented by conglomerate beds occur in Early Permian Barakar strata of Talchir coalfield and Late Mesozoic Bagra Formation of Satpura basin. The palaeosols vary in thickness from 4 m to 25 m and are characterised by red brown clay with mottles, rootlets, slickensides, ferruginous concretions and calcareous veinlets. The palaeosols are hydromorphic and are developed under poorly drained to well drained groundwater conditions. Even where the palaeosols are not present, the bedrock displays evidences of deep weathering. These probably represent the earlier topographic positive areas affected by physical weathering and intense groundwater activity.

Geochemistry of Komatiitic Basalt Dyke from Schirmacher Oasis, Queen Maud Land, East Antarctica

Abstract: Geochemistry of a Neoproterozoic/Phanerozoic basalt dyke of komatiitic affinity, in the Precambrian metamorphosed gneissic terrain of Schirmacher Oasis, Queen Maud Land, East Antarctica is reported here. The dyke is composed of olivine (Fo 87-90 ) which is largely pristine, clinopyroxene, magnesiochromite and devitrified glass. Clinopyroxene exhibits microspinifex texture. It has moderately high MgO (14.10-15.10 %), Cr (569-813 ppm), Ni (457-629 ppm) and low K 2 O (0.46-0.68 9%) and TiO 2 , (0.93-1.00 %) contents and high CaO/AI 2 O 3 (1.11-1.22) ratios. The dyke shbws Al-depleted (low Al 2 O 3 , TiO 2 , = 8.36-8.72, depleted HREE Gd N = Yb N = 1.66-1.96) signature. suggesting that the source magma was generated by low degree of partial melting of the mantle with garnet in the residue. LREE enrichment (La N /Yb N = 3.01-3.51) and negative Nb anomalies in the dyke samples further suggest crustal contamination of the source magma during ascent through the continental crust.

On the Discovery of Middle Eocene Larger Foraminifera from a Limestone Bed in Churu District, Rajasthan

Abstract: Definite Middle Eocene larger foraminifera has been found in the limestone at Sandwa, Bidasar area, Churu district in the Nagaur-Ganganagar basin, Rajasthan. Nummulites Cf. Obtuses (Sowerby) 1840 with two forms viz., A form (Dia. 2.8 mm) and B form (Dia. 9 mm) are observed. In the type area of Kachchh, N. Obtuses has been assigned the age of Middle Eocene. This find assigns the limestone bed to Jogira Formation and it also extends the limits of the Eocene Sea in Rajasthan by 80 km towards east.

Metamorphism of the Inverted Sequence in Himachal Himalaya: A Study from the Kullu-Rohtang Pass-khoksar Section

Abstract: An inverted metamorphic gradient has been documented within the rocks of the Kullu-Rohtang Pass-Khoksar region, with increase in grade of metamorphism from biotite through garnet, staurolite and kyanite to sillimanite zones. Microtextures, mineral equilibria and geothermobarometry of mineral assemblages indicate deformation at a minimum temperature of 500°C and 4.7 kbar pressure in the Kullu region to a maximum temperature of 635°C and 6.8 kbar pressure in the Rohtang Pass region of Higher Himalaya. The lower arnphibolite facies rocks further north of Rohtang Pass indicate P-T conditions of 4.5 kbar and 450°C respectively. The range of P-T conditions imply tectonic burial of 16 to 23 km and geothermal gradient variation of 31 °C/km to 28°C/km. There is a maximum P-T difference of 2100 bars and 135°C upsection between samples near Kullu to samples along the Rohtang Pass, with dP/dT values of around 16 bars/°C. The inverse metamorphism of the region is due to synto post-metamorphic folding of isograds accompanied by thrusting of normal Barrovian metamorphic sequence, that is subsequently followed by a retrogressive cooling path during exhumation.

Geology of Part of Warwan Valley, Doda District, Kashmir Himalaya

Abstract: Systematic geological mapping of an area of about 1000 sq.km.in the Warwan valley by the authors brought out a stratigraphic succession ranging in age from Proterozoic through the Jurassic which is represented in the ascending order by the Proterozoic Salkhala Group and the formations of Palaeozoic Ramsu-Machhal, Lolab, Karihul, Margan, Muth Quartzite, Syringothyris Limestone, Fenestella Shale, Agglomeratic Slate, Panjal Volcanics and Zewan, and Mesozoic Khunamuh, Khrew, Wuyan and Drungam. The Jurassic sequence in the area, designated as the Drumgam Formation, occurs as isolated outliers resting over the upper Triassic rocks with an angular unconformity in Drumgam- Kelnar area. Structurally, the area has experienced polyphase deformation, with atleast three distinct phases of folding, the best example being the Warwan valley Anticline, whose eastern limb is overturned. A pronounced unconformity between the Salkhala (Precambrian) basement and the overlying Palaeozoic-Mesozoic succession occurs in the southern part of the area.