bluuebunny/crossref_metadata_2025 huggingface dataset:
An Ion Microprobe Study of Single Zircons from the Amet Granite, Rajasthan
Authors: Wiedenbeck M. , Goswami J. N. , Roy A. B.
Published: November 2024

We have lIsed an ion microprobe to measure 207Pb/206Pb ages on carefully selected ~20 μm domains of single zircons from two samples of the Amet Granite. A sample of the Amet Granite, consisting of a strongly foliated augen gneiss, yields a minimum crystallization age of 1641±14 Ma (1s). From a second sample, collected from an aplite dyke which cross-cuts the foliation of the augen gneiss, we calculate a minimum emplacement age of 1766±16 Ma; both these ages are based on a dynamic background correction of 0.01 c/s.

As part of this study we conducted 30 analyses of an internal standard which has a published, concordant age of 2631±4 Ma. Our data suggest that a low intensity dynamic background (=0.01 c/s), comparable to the 204Pb count rate, is present within our system. This background could, in principle, lead to considerable uncertainties when calculating 206Pb/204Pb ages for young samples which have low radiogenic 206Pb concentrations. We believe an inaccurate background correction is the most likely explanation why the cross-cutting dyke yields an apparent age which is older than that obtained from its host rock. Assuming that the dynamic background was negligible at the time of its analysis. we recalculate an age of 1646±19 Ma for the dyke sample which is statistically indistinguishable from the age of the augen gneiss. The use of small geometry ion microprobes for obtaining 207Pb/206Pb age is best suited for older and radiogenic Pb-rich zircon, when such a low intensity background becomes less significant.

Our results indicate that the crystallization of the Amet porphyritic granite, the tectonic emplacement of the nearby mid-Proterozoic Sand Mata granulites and the subsequent deformation are the products of a single tectonic cycle which was completed by ~ 1.64 Ga.
Regional Stratigraphy of Quaternary Deposits in Parts of Thar Desert, Rajasthan
Authors: Sundaram R. M. , Rakshit P. , Pareek S.
Published: November 2024

Quaternary stratigraphy of a part of Thar desert, Rajasthan is proposed based on the correlation of depositional sequences in Kantli-Ghaggar basin, Luni basin, Sambhar lake and Jaipur area. The Quaternary sediments comprising the fluvial, lacustrine and aeolian deposits are associated with distinct pedologic events which show uniformity in succession even over these widely separated areas. The lithosequences and geomorphological characteristics along with pedogenic evidences are considered in classifying the Quaternary sediments, giving an informal nomenclature, into five formations namely Bikaner Formation, Churu Formation, Sambhar Formation, Jaipur Formation and Luni Formation, Each of these formations consists of fluvial, lacustrine and aeolian units excepting the Jaipur Formation which consists of only fluvial unit. The onset of Quaternary period marked a major transformation from humid, tropical to arid, desertic conditions which continued with periods of comparative wetter and drier phases.
Temporal Patterns of Palaeoflows of Middle and Upper Siwalik Subgroups, Jammu
Authors: Pandita S. K. , Bhat G. M.
Published: November 2024

This paper embodies the results of palaeocurrent analysis of two stratigraphic sections exposed at Parmandal-Uttarbani and Papar-Nad, Jammu. The general palaeoflow patterns are due south-southwesteriy with the temporal palaeoflow variations of 40°-183° and 41°-144°for the Middle and Upper Siwalik Subgroups respectively. In the Middle Siwalik Subgroup of Papar-Nad section and Upper Siwalik Subgroup of Parmandal-Uttarbani section, four palaeoflow reversals have been recorded. The temporal palaeoflow patterns and the reversals are related to the tectonic episodicity of the intrabasinal tectonic structures and the basin margin activity.
Geomorphic Controls of the Chittamgondi Bauxite Deposit, Visakhapatnam District, Andhra Pradesh
Authors: Prakash P. , Ramana Rao K. L. V.
Published: November 2024

Bauxite cappings occur discontinuously, along a linear stretch amidst the Eastern Ghuts comprising khondalite and charnockite groups of rocks, in the States of Andhra Pradesh and Orissa. These cappings/deposits, by virtue of their proximity to the eastern coastline of India, are christened as the East Coast Bauxite deposits.

The East Coast Bauxites of Andhra Pradesh include the Anantagiri, Chintapalli, Gurtedu and Paderu groups of deposits. The Anantagiri group comprises Galikonda, Chittamgondi, Raktakonda and Kutuki deposits. The Chittamgondi bauxite deposit, charucterised by multi-directional slopes, is preserved in a sickle shaped synformal structure. Furthermore, the maximum thickness of bauxite, viz., 54 m, amongst the East Coast Bauxite deposits, investigated so far, has been recorded in it. As has already been established for other East Coast Bauxite deposits, the geomorphological setup and morphometry have played a pivotal role in the formation of the Chittamgondi bauxite deposit.
Chromite Alteration at Boula-Nausahi Igneous Complex, Orissa
Authors: Mohanty J. K. , Sahoo R. K. , Paul A. K.
Published: November 2024

During Serpentinization of the ultramafic rocks, the accessory chrome spinels are altered at grain margins and/or along fractures to highly reflecting phases of ferritchromit and magnetite which occur as rims around parent chromite. Of these two altered phases, ferritchromit exhibits greater compositional variation. Electron probe microanalysis data indicate that these phases are rich in Fe and poor in Cr, Al and Mg with respect to parent chromite. Magnetite rim is characterised by extreme iron enrichment and marked depletion of Cr, Al and Mg whereas ferritchromit represents intermediate chemical composition between parent chromite and the magnetite outer rim. This compositional variation is due to solid state diffusion of elements from chromite outwards during serpentinization. Textural features, chemical composition and presence of chromiferous serpentine attest genetic relationship between serpentinization and chromite alteration.
Nature of Aquifer in Parts of Granitic Terrain in Mahabubnagar District, Andhra Pradesh
Authors: Raj Pradeep , Nandulal L. , Soni G. K.
Published: November 2024

Hydrogeological studies in the granitic terrain in parts of Mahabubnagar district, Andhra Pradesh, indicate a fairly thick and well distributed weathered zone, linear zones of fractures and deep water levels. The higher yields of some of the bore wells are due to the presence of N-S or E-W fractures. Pumping tests on 23 dug wells and three bore wells drilled within the weathered zone indicate a lower transmissivity values when compared with the pumping tests conducted on four bore wells which encountered fractured zones.

The gross ground water extraction per unit area hardly varies in sampled areas that form sman second order basins, irrespective of well density or type of wells. The number of dug wells drying-up in parts of the area is proportional to the success of the bore wells in the area. It suggests that new and deeper wells are only replacing the older, shallower dug wells and that the deeper fractured zone aquifer and shallower weathered zone aquifer are well connected.

This study also shows that the limiting factor for ground water development is not the nature of the aquifer but the quantum of recharge to it. Hence, artificial recharge structures must be planned to improve availability of ground water in the area.
Heavy Mineral and Geochemical Studies of Lower Bharathapuzha Sediments, Kerala
Authors: Rajendran S. , Karthikeyan P. , Seralathan P.
Published: November 2024

Size specific abundance of heavy minerals (HM) in sediments of lower Bharathapuzha indicates an increase towards finer sizes, with the average maxima at ASTM +170. HM content in the bulk sample is similar to that of ASTM +60. Opaques, hornblende and pyroxenes are responsible for more than 90% variability. Garnet, monazite, zircon and sillimanite are least abundant. Hornblende, pyroxene and garnet are enriched in ASTM +60 but depleted in ASTM +230, whereas opaques show a reverse trend. HM content of bulk is similar to that of ASTM +60 and +120.

Heavy metal distribution has also been examined and the order of abundance is Fe>Mn>Ni>Cr>Zn>Pb>Cu>Cd. Bulk samples show the lowest content. Mud fraction is emiched in metals, i.e., more than five fold for Zn, Cu and around three fold for Ni, Cr, Mn and Fe. The difference of metal abundance between HM and mud fraction is only marginal for Ni and Pb. In HM, Cd, Cu and Zn content are very low whereas Cr, Mn and Fe are enriched. EF (Enrichment Factor) values of Cu, Zn, Cr and Mn are close to crustal abundance whereas Cd and to a small extent Pb show relatively high values possibly resulting from anthropogenic contributions.
Economic Viability of Manganese Nodule Mining in India: A Discussion
Authors: Manickam S. , Victor Rajamanickam G. , Benjamin R. E.
Published: November 2024

A comprehensive analysis of the economic viability of manganese nodule mining in India through the adoption of the standard capital budgeting techniques is attempted. The study includes both 3-metal plant (Copper, Nickel and Cobalt) and 4-metal plant (Copper, Nickel Cobalt and Manganese). Most of the studies carried out in the developed countries in the past conclude that this new ocean mining venture is not eccnomicaily viable. Hence, in this study, an attempt is made to find out any change that leads to significant improvement in the viability of the project by comparing the economic status of the industry between two periods, June 1987 and July 1990. The results of the research show that the Internal Rate of Return (lRR) of the 3-metal plant is 8.1% in June 1987 prices and the IRR for the 4-metal plant is 15.2%. But the IRR of 3-metal plant is 45.3% in July 1990 prices and 40.4% for the 4-metal plant. The results clearly point out that the project becomes viable in 1990 prices. This vast improvement in the economic status of this industry can largely be attributed to the enormous hike in the annual revenue of the project. Thus, the deep ocean holds out a beacon of hope to the world in general and India in particular for future supply of nodule metals.
Petrographic Criteria for Freshwater Diagenesis of Saurashtra Miliolites
Authors: Bhatt Nilesh , Patel M. P.
Published: November 2024

The miliolites of Saurashtra Peninsula represent reworked bioclastic sand accumulations under the varying palaeoclimatic conditions during the Late Quaternary period. Their origin, whether marine or aeolian, forms a matter of controversy. These rocks comprise medium to fine grained allochems along with minor amount of detrital grains cemented together by non-ferroan, low magnesian sparry calcite cement exhibiting various ultrastructures. The intragranular porosity, geopetal infilling, dripstone-drapstone, meniscus and dogtoothspar cements suggest vadose condition while the presence of isopacholls rim and blocky void filling cements indicate their formation in phreatic freshwater environment.
On the Problem of Age and Genesis of Bedhaghat Water Falls (Jabalpur), Madhya Pradesh
Authors: Ganjoo R. K. , Rajaguru S. N. , Gupta Avijit
Published: November 2024

Reasonably convincing evidences of neotectonic activities in the Central Narmada Valley have come to light. The geomorphic investigation of litho-sections at Bedhaghat, near Jabalpur and Siddhaghat highlights the occurrence of such event in geologically younger times. The integration of observations has further helped in understanding the genesis and dating the waterfall at Bedhaghat.
Geochronology and Geochemistry of the Lingtse Gneiss, Darjeeling - Sikkim Himalaya: Revisited
Authors: Paul D. K. , Mcnaughton N. J. , Chattopadhyay S. , Ray K. K.
Published: November 2024

Foliated augen gneisses with streaky character, such as the Lingtse Gneiss of Sikkim-Darjeeling area, occur throughout the Himalaya. The Lingtse Gneiss is highly deformed and Occurs as thin tabular bodies. Considerable textural variation is noticed depending on the intensity of deformation and grain growth. The rocks are peraluminous and show fractionated REE pattern (Lan/Lun = 1.2-6.8). These gneisses were previously dated at 1075 and 2034 Ma by Rb-Sr method. The results of the present isotopic age determination by Rb-Sr and Pb/Pb methods indicate ages of 1678 ± 44 Ma and 1792 ± 45 Ma respectively. The variability and scatter of isotopic composition are believed to reflect imprints of tectono-thermal events.
Statistical Structure of the Aeromagnetic Anomaly Field Over the Cuddapah Basin and Adjoining Terrain: Implications in Interpreting Structure and Tectonics
Authors: Bhaskara Rao D. S. , Rao Ch. Rama , Atchuta Rao D.
Published: November 2024

The statistical structure of the aeromagnetic anomaly field over an area of approximately 30,000 sq. km of parts of eastern Dharwar craton and the western parts of Cuddapah basin has been studied. The distribution of statistical moments of aeromagnetic field showed two magnetically different zones, viz., one towards north of 14°45'N Lat., and the other to the south of it. Directional filtering operations over the exposed granite-greenstone terrain and the adjoining intracratonic Cuddapah basin has clearly brought out an ENE to E-W trending long linear possibly related to a deep seated tectonic feature. This mega lineament separates this part of the crust into two zones of different magnetic character. Filtering operation over the aeromagnetic data applying sequential trend suppression in E-W, NW-SE and ENE-WSW directions has clearly brought out magnetic trends striking nearly N-S. These nearly N-S trends may reflect the structures that controlled the development of greenstone belts or the structures resulted during the E-W compressional event.
Agnostid Fauna from the Cambrian of Spiti
Authors: Sahni A. K. , Sudan C. S.
Published: November 2024

An agnostid fauna from the Middle Cambrian (Peronopsis-Oryctocephalus zone) of Parahio valley, Spiti is described. It includes Peronopsis amplaxis. Peronopsis sp., Pagetia griesbachi and Pagetia sp. This assemblage is correlated with S olenopleura-Tonkinella zone of Kashmir and also with Ptychagnostus gibbus zone of Australia and North America.
Trace and Rare Earth Elements Geochemistry of Alkaline Rocks of Sarnu-Dandali, Harmer, Rajasthan
Authors: Shastry Anant , Kumar Santosh
Published: November 2024

The alkaline rocks belonging to ijolite series and carbonatites constitute the Sarnu-Dandali igneous complex (68.5 Ma) associated with Precambrian acid volcanics. Trace elements including REE of ten selected Late Cretaceous rock-types viz. melteigite, melanephelinite, phonolite, carbonatite, basalt and Precambrian rhyolites of SDIC have been examined and discussed. The data of alkaline rocks suggest their derivation from an alkaline (ijolitic) magma formed by the partial melting of mantle source. Ba-Sr-REE enriched carbonatites possibly represent an immiscible split from nephelinite. The basalt (Hawaiite) represents a subalkaline magmatic pulse unrelated to alkaline suite. The associated Precambrian rhyolites have formed by a combination of magmatic processes such as partial melting, fractional crystallization and/or magma-mixing.
Geochemistry and Petrogenesis of Hanuman Tibba Granite of Kullu Valley, Himachal Himalaya
Authors: Islam R. , Bist K. S. , Chaudhuri B. K. , Rawat B. S. , Purohit K. K.
Published: November 2024

A maiden attempt has been made to study the far-flung Hanuman Tibba Granites of Kullu valley, Himachal Pradesh. The granite has intruded the low grade Haimanta (-Lahaul) Formation which tectonically overlies the Rohtang Gneissic Complex. Integrated field, petrographic and geochemical studies have revealed that it is peraluminous S- type granite derived from sedimentary protolith. Compositional difference in terms of depletion of Fe, Mg, Ti, Ca, Sr, Zr and enhancement of Sit K and Rb from margin to core of the granite body is consistent with fractional crystallization process.

The emplacement of Hanuman Tibba Granite on the same tectonic level as Jispa and Ratilaman granite (500±ma) in adjacent Lahaul-Spiti region suggests a Cambro-Ordovician age for the Hanuman Tibba Granite.
Fault Segmentation and Earthquake Hazard Zones in Deccan Trap Region: Gravity Evidence
Authors: Ramachandran C. , Kesavamani M.
Published: November 2024

Detailed structural interpretation of the regional gravity map over the Deccan traps has brought out a number of major structural discontinuities (fault/fractures), particularly the E-W features whlch were not delineated by earlier investigators. The most significant among them is the major E-W fault from west coast to east coast along Bombay-Latur-Hyderabad-Bhadrachalam-Visakhapatnam (BLHV fault). Several features of the BLHV fault suggest it to be a major reactivated strike slip fault. The structural scenario presented in this paper will have great implications in earthquake studies in Deccan trap area. Based on some aspects of fault segmentation technique for earthquake hazard and from the structural interpretation of the regional gravity map over Deccan traps, several zones are identified which could be termed as earthquake hazard zones. These hazard zones are typically located at: (1) the segment boundaries or fault steps of BLHV and other major E-W faults, (2) in many cases are associated with gravity low nosings which possibly reflect buried granite intrusions (regarded as asperities or barriers in the context of seismicity), and (3) intersection of major E-W faults with other transverse structural trends (fault/fractures). The areas where the major E-W faults terminated against the west coast fault system can also be important in terms of future seismicity. The recent seismicity in the Deccan trap, area is inferred to be due to the reactivation of the major E-W faults due to the still continuing convergence of India with Asia.

The present work, for the first time, demonstrates the importance and application of fault segmentation technique in earthquake hazard studies in Deccan trap area, and also the full potential of gravity interpretation in such studies.
Spinifex Textured Peridotitic Komatiite from Nuggihalli and R.N. Pur Schist Belts, Karnataka
Authors: Jafri S. H. , Subba Rao D. V. , Ahmad S. M. , Mathur Ramavati
Published: November 2024

Spinifex textured ultramafic rocks occur at Bhaktarahalli in Nuggihalli schist belt and as an enclave within the Peninsular Gneiss near Dodda Gudda, Holenarasipur belt in Hassan District. They have Komatiitic chemistry pointing to ultramafic volcanism in the Dharwar Craton during the Archaean Era.
Glacial Erratics in the Higher Himalayan Region of Lahaul, Himachal Pradesh: Their Geomorphological Significance
Authors: Prashra K. C.
Published: November 2024

Two levels of glacial erratics of granitic rocks located at about 280m and 1250m above the present river level have been identified in the Higher Himalayan region of Lahaul, Himachal Pradesh, which may possibly correspond to advancing and waning phases of the valley glacier. The erratics have been transported over a distance of about 4 km to 28 km from their respective provenances. The appreciable difference in altitude between the two levels of erratics and that of the present river course suggests a considerable uplift of this part of the Himalaya during the Quaternary period.
Geothermometry and Oxygen Barometry of Coexisting Iron-Titanium Oxides of Majhgawan Diamondiferous Pipe, Madhya Pradesh
Authors: Mukherjee Abhijeet , Rao K. S. , Bandyopadhyay D. , Roy Gautam , Chatterjee A. K.
Published: November 2024

Geothermometry of the coexisting magnetite-ilmenite (Mt-Ilm) pair from Majhgawan diamondiferous pipe indicates a temperature of 1150°C. The values of fO2 T and P fall in the equilibria field defined by iron-wustite (IW) and wustite magnetite (WM) indeating depth of sampling of about 155km and pressure of 46kbar.
Hydrogeological Conditions and Optimum well Discharges in Granitic Terrain in Parts of Nalgonda District, Andhra Pradesh, India
Authors: Narasimha Reddy T. , Raj Pradeep
Published: November 2024

Ground water in study area underlain by peninsular Gneissic complex occurs in unconfined conditions in weathered zones and semi-confined to confined conditions in fractured zones. Productive fractured zones define narrow linear tracts closely corresponding to surface drainage. Fluoride content of ground water is low mostly in topographic highs and to lesser extent in tank beds or tank commands and in areas where fractures are not connected with fluoride bearing granites. For potability, most wells were drilled in topographic highs and some around tanks.

The aquifer is highly complex (anisotropic and heterogeneous) needing critical analysis to assess performance of wells, as recently yields of a large number of borewells drilled in granitic terrains of Andhra Pradesh are reported to have declined. This is attributed mostly to direct interference with other wells, improper construction of wells leading to silting and general decline in water levels due to various reasons. But rarely, it is realised that these aquifers are laterally limited. In this study pumping tests for 500 to 1000 minutes i.e., 2 1/2 to 3 log cycles of time were carried out and the data was analysed using graphical methods of Cooper and Jacob and Theis recovery method. [n four cases the test data was analysed by a micro processor based simulation technique. Optimum discharges were calculated keeping in view the effects of 'no-flow' boundaries, effective available drawdown and other field parameters. This has indicated that the optimum discharges of the wells are in general between 60% to 80% of the yields recorded during drillng.
A New Occurrence of Sapphirine in the High-Grade Pelitic Gneisses of Usilampatti, Tamil Nadu
Authors: Subba Rao D. V. , Nirmal Charan S. , Moeen S.
Published: November 2024

Sapphirine is found in the pelitic gneisses of Kosavankovilpatti near Usilampatti in Tamil Nadu. It is intimately associated with melt products and the associated minerals are garnet, biotite, orthopyroxene, plagioclase, mesoperthite and K-feldspars. The sapphirine-bearing rock is characterised by (i) enrichment of MgO, depletion of SiO2 (ii) absence of coronas and symplectites, (iii) presence ofmesoperthites (iv) high XMg values of the associated minerals and (v) high P-T conditions (855±20°C and 8.0±O.3 Kb) in contrast to the adjacent sapphiri ne absent rocks (750-800° and P of 6.5-7.5 Kb). This occurrence of prismatic sapphirines is in contrast with the reported sapphirine occurrences where it occurs as symplectites and coronas defining a decompression path (T= 700°C and p 5-7 Kb) in the adjacent Kodaikanal massif. It is suggested that the sapphirine being reported is of prograde origin.
R-Mode Factor Analysis, and Its Implications on the Geochemistry of Nishikhal Manganese Deposit, Raigada District, Orissa
Authors: Nayak B. K. , Mohanty Swati , Rajeev  , Sahoo R. K.
Published: November 2024

Normalised major and trace element data of manganese ores from Nishikhal are processed by using R-mode factor analysis of correlation matrix. Twenty major and trace elemental variables are expressed in terms of 3 common (rotated) factors to understand the mineralogical occurrences and the processes of formation of the manganese deposit. Varimax factor scores are used to classify in a finer detail the manganese ore types.
Marine Magnetic Anomalies as a Link Between the Granulite Belts of East Coast of India and Enderby Land of Antarctica
Authors: Murthy K. S. R. , Malleswara Rao M. M. , Venkateswarlu K. , Subrahmanyam A. S. , Lakshminarayana S. , Rao T. C. S.
Published: November 2024

Magnetic data of the eastern continental margin of India (ECMI) helped in demarcating the offshore extension of the granulite belts of east coast of India and their possible link to those of the East Antarctica. Short wavelength and high amplitude negative magnetic anomalies (200 to 1600 nT) are observed over the northern part of ECMI between Kakinada and Chilka lake and also off Madras shelf, the coastal regions of which are associated with granulite facies rocks . This part of the shelf is associated with structural lineaments with predominant NE-SW trends . In contrast, the offshore basins off Cauvery, Krishna - Godavari (K-G) and Mahanadi rivers are associated with subdued positive anomalies (less than 200 nT) indicating subsidence off these basins by heavy load of Phanerozoic/younger shelf sediments. Structural lineaments with NW-SE or W-E trends delineated over these basins are related to the offshore extension of these rift related Gondwana grabens. Similarity in the trends of the magnetic anomalies and the granulite facies on the east coast of India and their correlation with the granulite belt of Enderby Land of Antarctica supports the view that the entire region comprised of a single and stable block of granulite rocks prior to the fragmentation of the Gondwanaland. The study also suggests probable continuation of Mahanadi and Godavari grabens into East Antarctica.
Dune Associated Calcretes, Rhizoliths and Paleosols from the Western Continental Shelf of India
Authors: Purnachandra Rao V. , Thamban M.
Published: November 2024

The calcareous deposits on the western continental shelf of India, off Bhatkal (water depths 50 to 58 m) occur as crusts, sheets, cylinders and reddish brown mudstones. The outer layers of the crusts are micrite-dominated and beneath this layer detrital/carbonate sands with thin heavy mineral laminations are found. Textural studies indicate that the detrital sands are derived from dunes. Drusy calcite and neomorphic calcite cements are associated with the sands. Sheet deposits contain coarse calcareous component-dominated layer within micrite layers and abundant micrite cements. These are similar to dune associated calcretes.

Cylinders are rhizoliths and show different stages of root calcification. Circular bodies. about 0.15 mm to 0.70 mm diameter, interpreted as vascular cylinders of the root tissues are typical. Radial fibrous calcite and spar calcite with inclusions indicate neomorphic cements. Reddish brown mudstones contain calcified root-hair sheaths, micrite glaebules and reworked pollen suggesting that these are indurated soils. X-ray diffraction studies indicate the presence of ferroan calcite, quartz, pyrite and dolomite in rhizoliths and ferroan calcite, goethite and quartz in mudstones. Mudstones and some rhizoliths are Fe-rich and some other rhizoliths are Fe-poor but enriched with Mg and Mn. The particulate matter in the calcareous deposits were initially at the proximity of the coast and cemented by metastable calcites during the ultimate Pleistocene interglacial sea-level stands on the shelf. Pedogenic cementation processes overprinted and developed them into eolianites and paleosols during the subsequent Late Pleistocene sea-level regression. The compositional differences of these deposits were apparently controlled by type of sediments and associated sedimentary environments.
Variation of Crustal Velocity Structure in India as Determined from DSS Studies and their Implications on Regional Tectonics
Authors: Kaila K. L. , Sain Kalachand
Published: November 2024

The Indian subcontinent has been divided into six crustal velocity zones based on P-wave velocity structure obtained along 20 Deep Seismic Sounding (DSS) profiles, covered in India from 1972 to 1992. Zone - 1 consists of two parts: zone  - 1.a comprises the Dharwar craton, Cuddapah basin, Godavari graben and the Koyna region, and zone- 1 .b consists of the western margin of the Bengal basin and the Singhbhum craton. Zone - 2 covers the West Bengal sedimentary basin and the Mahanadi coastal basin. Zone - 3 includes Bundelkhand craton and the Vindhyan basin. Zone - 4 covers Cambay basin north of the Narmada lineament and the Aravalli - Delhi fold belt. Zone - 5 lies south of the Nannada lineament covering the Tapti graben extending up to the west coast of India. Zone - 6 comprises the northwest Himalaya up to the Nangaparbat including Jammu and Srinagar sedimentary basins. Detailed crustal velocity structures in these six zones have been described with their bearing on regional tectonics. Velocity structure of the lower crust in some of these zones, suggests that crustal underplating has played a very important role in the evolution of the Indian continental crust and lithosphere. Some petrological inferences have also been drawn for the Indian crust from crustal velocity zonation.
Pattern of Seismicity in Shillong-Mikir Plateau and the Orientation of Compressional Axis
Authors: Baruah Saurabh , Duarah Ranju , Yadav Dilip K.
Published: November 2024

The study of eleven years (1982-1993) of seismicity (focal depths<60km) in the Shillong-Mikir massif of N.E.R., India (25°-27°N) clearly delineates the pattern of activity within this region. The most important feature is a concentration of events in the depth range of 20 to 40 km where 70% of the activity took place. Minor seismicity prevails in the other ranges. The results from the focal mechanism solutions of 12 events of magnitude >5.0 ascertain thrust and strike slip type mechanisms within the depth range of <40km while dip-slip and normal type solutions are occurring in the range >40km. The compressional axis of most of the events is oriented along north-northwesterly direction.
Pyroclastics in the Late Proterozoic Formations of the Simla Himalaya
Authors: Bose U. , Nagal S. C. , Sharma N. L. , Prashra K. C. , Sharma V. K. , Bassi U. K.
Published: November 2024

Pyroclastics are found in all the late Proterozoic clastic formations of the Outer Krol Belt in the Simla Himalaya. The field and petrographic characters leading to identification of the pyroclastics are described here.
Turbidite to Storm Transition Sedimentation during Early Carboniferous, Kashmir Himalaya
Authors: Bhat G. M. , Singh Rajinder , Pandita S. K.
Published: November 2024

This work, based on sedimentological data collected from two stratigraphic sections at Lambar and Malvat (Banihal area), reports the turbidite to storm influenced sedimentation of "Syringothyris Limestone" sequence, Kashmir Himalaya. An upward progresssion of the sequence reflects the depositional record of fine grained turbidite to storm - and wave - influenced sedimentation. Sedimentary structures like short wave length symmetrical ripples. flat lamination, thin graded bedding and structures in muddy siltstones suggest deposition in low energy, wave influenced settings, The storm influenced sediments display hummocky, cross stratification. skolithos ichinofacies, granule/shelly lags, mega ripples, low angle cross lamination and convolute lamination. The whole sequence is interpreted to represent episodic storm influenced sedimentation in a shallow basin, largely controlled by tectonic activity, The Markov Chain models structured for this sequence also suggest episodic sedimentation and do not show any cyclicity,
Geochemistry of Rajapur and Puttur Thermal Springs of the West Coast, India
Authors: Ramanathan A. , Chandrasekharam D.
Published: November 2024

Thennal springs of Rajapur and Puttur (Irde and Banduru) are of low-temperature and low-flow type. Though they are located at two different geological set up, they fall in Na-HCO3 facies . The imprints of basalt - thermal water interaction at Rajapur and local equilibration of doleritic dyke with the thermal water of Irde is deduced. The reservoir of the Rajapur thermal spring is likely to be located in the Precambrian formations, as that of Puttur thermal springs and hence the chemical processes undergoing in these systems are similar. The reservoir temperatures estimated using chemical geothermometers are about 200°C and >120°C for the Puttur and Rajapur thermal springs respectively. Illite, K-mica. chlorite. kaolinite. Ca-montmorillonite and philipsite are the expected secondary minerals in the system.
Grain Size Studies on the Nearshore Sediments of Jaigad, Ambwah and Varvada Bays, Maharashtra
Authors: Rajamanickam G. V. , Gujar A. R.
Published: November 2024

Bivariate plots of the textural parameter data suggest overlapping environments. Such as river/beach to JB, beach/dune/river to AB and dune/beach to VB sediments.
Internally Consistent Geothermobarometers in the System FeO-MgO-Al2O3-SiO2-H2O Involving Garnet, Cordierite, Aluminosilicate and Quartz and their Application to Metapeiites
Authors: Dwivedi S. B. , Mohan A. , Lal R. K.
Published: November 2024

Reactions involving garnet, cordierite, aluminosilicate and quartz in FMASH system are calibrated as geothermobarometers, namely 1/2 Fe-crd + 1/3 Pyrope = 1/2 Mg-crd + 1/3 Almandine (1); 2 Almandine + 4 sillimanite/andalusite + 5 quartz = 3 Fe-crd (2 and 4); and 2 Pyrope + 4 sillimanite/andalusite + 5 quartz = 3 Mg-crd (3 and 5).

T = [6170+O.031(P-1)-400(XFe-XMg)Crd-A]/(RlnKD+2.812+B) (1)

A= 166 X2Mg-506 X2Fe+680 XFeXMg+336 (XCa+XMa) (XMg-XFe)-

XCa - 358 XMn and B = 1.5 XCa

For Fe and Mg end-member reactions involving sillimanite, the following geobarometric formulation is obtained:

PFe=1+[{(24.02-6RlnKFe)T-17369}/4.003]                                  (2)

PMg=1+[{(7.238-6RlnKMg)T+19640}/3.82]                                  (3)

Similarly for reactions involving and alusite, PFe and PMg expressions are : PFe=1+[{(26.04-6RlnKFe)T-19471}/3.86]                                    (4)

PMg = 1+[{(9.25-6RlnKMg)T+17536}/3.68)                                  (5)
A Genetic Re-Iinterpretation of the Shore Parallel Sand Ridges on the Balasore-contai Floodplain, W. Bengal and Orissa
Authors: Banerjee P. K. , Goswami S. , Chatterjee S.
Published: November 2024

Linear mounds of sands, spread over 400 km2 in the Balasore-Contai floodplain and aligned parallel as well as close to the shoreline are not past strandline markers. It is suggested that these are compound products of fluviatile deposits capped by aeolian accumulations during late Holocene, albeit undated, arid intervals. The mounds were stabilished by soil and vegetation cover and are presently under anthropogenic attack.
Sulphur Isotopic Study on the Vein-Type Baryte from Vemula in the Vempalle Formation of Cuddapah Basin, Andhra Pradesh
Authors: Dhana Raju R. , Prasad R. N. , Pandey D. D. , Jeyagopal A. V. , Deshmukh R. D.
Published: November 2024

Baryte at Vemula near to the southwestern margin of Cudapah Basin occurs as a vein-type deposit discordant to both the carbonate rocks of Vempalle formation and its intrusive dolerite. S-isotopic data on the baryte have a range of d34SCDT between +16.2‰ and +23.3‰ whereas the coexisting chalcopyrite has a restricted range between +10.9‰ and +11.4‰. The average value of d34S of Vemula baryte (+20.8‰) differs much from that of magmatic rocks (0‰ to +2.5‰), metamorphic rocks (+3‰) and sediments of continental margins, platform areas and geosynclines (-12.5‰ -17,1‰), but is similar to that of sea water (+20‰) which appears to be the source for sulphur. The narrow range of d34S of baryte and chalcopyrite points to a uniform source with their sulphur possibly derived from sea water sulphate by bacteriogenic reduction.
Distribution of Organic Matter and Calcium Carbonate in the Shelf Sediments off Penner River, East Coast of India
Authors: Seetharamaiah J. , Swamy A. S. R.
Published: November 2024

Organic matter and calcium carbonate in the shelf sediments off Penner river are mainly controlled by the texture of the sediments. The outer shelf (30-50 m depth) sediments of the southern and northern parts have a higher content of organic matter (1.2 to 2.22%). The sharp differences in organic matter content (varies from 0.8-1.6%) and fine nature of the sediments at the river mouth reveals detrital contribution. A calcium carbonate rich zone (30-40%) associated with coarse sands occurs opposite to Penner river mouth (20-50 m depth). The source for high concentration of calcium carbonate in the coarse sands (relict) are molluscan shells, shell fragments and foraminifera indicative of the in situ origin . It is inferred that the calcium carbonate supports that the coarse sands are stillstand deposits admixtured with present conditions.
Petrogenesis of the Mandi Gabbroic Rocks, Lesser Himalaya, India
Authors: Chaudhri Naveen , Gupta L. N.
Published: November 2024

The gabbroic rocks of Mandi area occur as an oval-shaped, 500 m thick intrusive body within the Mandi granite. The central zone of the body is made up of fresh gabbro and it grades into metagabbro and epidiorite towards the margins. The relatively high abundances of Ti, AI, Ca and Mg in clinopyroxenes of the central part as compared to the clinopyroxenes of the marginal part suggest different rates of cooling within the Mandi gabbroic body. The zoned plagioclases have calcic-rich cores and calcic-poor rims. The Al - (Fe+Ti) - Mg values and incompatible trace element ratios of the rocks indicate tholeiitic nature of the body. The discrimination diagrams based on major elements as well as immobile minor and trace elements suggest that these rocks are of MORB type. However, the chemical characteristics like negative Nb, Ti and P anomalies in the primordial mantle-normalised spiderdiagram together with low TiN and ZrN ratios testify that the Mandi gabbroic rocks are akin to low-Ti continental flood basalts. [Mg]-[Fe] modelling, incompatible versus compatible trace element data and lower Ni abundances for the given Mg contents suggest 10-15 % fractional crystallisation of olivine after the rocks were generated by partial melting under pressure conditions ranging between 25 and 40 kb. The intrusive appears to have formed by low degree of partial melting of a non-pyrolitic metasomatised mantle source that was heterogeneous with respect of Zr and Fe/Mg ratios.
Eustatic Changes and the Evolution of Palaeogene Larger Foraminifera - A Numeric Analysis
Authors: Saraswati Pratul Kumar
Published: November 2024

Sea-level change is known to have influenced the evolution of marine life. It is examined here how faunal diversity and rates of taxic evolution are related to change in sea-level and stability of the sea-level cycles. Evolutionary metrics of Palaeogene larger foraminifera are calculated and stability of sea-level cycles are determined using number and average duration of third order cycles in each stratigraphic interval. Generic diversity and the rates of origin and extinction individually do not show one to one correspondence either with transgression-regression or with the stability of the sea-level cycles. The rate of extinction relative to the rate of origination, however, is found to be significantly affected by the stability of the sea-level cycles. The rate of extinction exceeds the rate of origin during the periods of low stability. Regression, assisted by unstable sealevel cycles and possibly sharp climatic deterioration caused extinction maxima of larger foraminifera in Late Eocene.
Geochemical Characteristics of the Granites of Bundelkhand Massif, Central India
Authors: Mondal M. E. A. , Zainuddin Syed M.
Published: November 2024

The Bundelkhand massif comprises various types of granites. On the basis of field relations, three compositionally distinct granitic phases have been delineated. These are hornblende granite, biotite granite and leuco granite in stratigraphic sequence. The major elements variations against SiO2, display smooth trends which should be expected for a composite massif evolved by fractionai crystallization. The variations of incompatible elements compared to the compatible elements suggest a partial melting process for the evolution of the massif.
The Jabalpur Earthquake of May 22, 1997
Authors: Gupta H. K. , Chadha R. K. , Rao M. N. , Narayana B. L. , Mandal P. , Ravi Kumar M. , Kumar N.
Published: November 2024

The Jabalpur earthquake of magnitude 5.8 occurred on May 22, 1997 along seismically active Narmada-Son Lineament (NSL) in central India, with its epicenter about 30 km southeast of Jabalpur. A maximum intensity Io = VIII on MM scale was observed in Jabalpur and surrounding region. The isoseismal map prepared for this earthquake shows NE-SW trend which in general agrees with the focal mechanism solution indicating thrust faulting along a ENE-WSW fault with minor strike-slip component. Several ground cracks mapped in meizoseismal area show a dominant N75° E trend. The damage pattern of the constructions clearly shows a strong correlation with lithology, structures and soil cover of the area. There are no foreshocks reported for this earthquake and only a few aftershocks are recorded. which warrant a close monitoring of this region.
Syntectonic Growth of Porphyroblasts over Crenulation Cleavages - An Example from the Precambrian Rocks of the Lunavada Group, Gujarat
Authors: Mamtani Manish A. , Karanth R. V.
Published: November 2024

Porphyroblasts are known to overgrow crenulation cleavages syntectonicaIly in crenulated schists. However, the timing of growth of such porphyroblasts remains a problem. Whilst some researchers believe that porphyroblasts can syntectonically overgrow crenulation cleavages during the genesis of the crenulation cleavage, there are others who believe that porphyroblasts overgrow crenulation cleavages during an episode of deformation which post-dates the deformation which resulted in the formation of crenulation cleavage. In the present paper we present microstructural . evidence of syntectonic porphyroblasts overgrowing crenulation cleavages from the mica schists of the Lunavada Group of Precambrian rocks occurring in Gujarat. It is concluded that syntectonic porphyroblasts can grow over crenulation cleavages during the same episode of deformation which resulted in the genesis of the crenulation cleavage.
Geology and Geochemistry of Basic Volcanics From the Sakoli Schist Belt of Central India
Authors: Roy Abhinaba , Bandyopadhyay B. K. , Huin A. K.
Published: November 2024

The Mafic volcanic suite exposed mainly in the eastern part of the Sakoli schist belt comprises the lower part of the Sakoli sequence. The samples are tholeiitic in composilion having moderate M-values (45-62) and lower abundances of Ni, Co and Cr indicative of evolved nature of the magma. Certain major and trace element characteristics and LREE enriched REE patterns suggest magma derivation by low degrees of partial melting of komatiite-like sources.
Groundwater Over Exploitation: A Case Study From Moje-Anepura, Kolar District, Karnataka
Authors: Ballukraya P. N.
Published: November 2024

Over a period of 15 years, as many as 84 bore wells were put into operation within an area of 160 hectares. The consequent groundwater over-exploitation led to serious decline in water levels as well as depth to producing zones resulting in the failure of a large number of borewells. The initial trend of increasing area under groundwater irrigation got reversed due to reduced availability of water. The cropping pattern also changed along with groundwater extraction pattern: from predominantly cereals to cash crops. The depth of borewells drilled has been on the increase each year as shallower aquifers dried up. The yield fluctuation in the pre-and post-monsoon periods has indicated that recharge is largely restricted to about 60m depth and therefore, the optimum depth of borewells in the study area should not exceed this limit. The present practice of tapping deeper fracture aquifers is a case of groundwater mining, without any aonual replenishment occurring and will lead to severe problems in the near future.
Carbon and Oxygen Isotopic Compositions of Infratrappean Limestones from Central and Western India and Their Depositional Environment
Authors: Bhattacharya S. K. , Jani R. A. , Tripathi S. C. , Lahiri T. C.
Published: November 2024

The lowermost formation of the Bagh Group, the Nimar Sandstone, was deposited in fresh water whereas the upper two formations, the Nodular and Coralline Limestones were deposited in marine environment There is a distinct signature of diagenetic alteration in the oxygen isotopic ratios but the carbon isotopic ratios did not change signi ficantly. The marine transgression from the continental Nimar period to upper Limestone period was extremely rapid in all four sections (Mogra, Rampura, Acharkunda and Bariya) examined. However, the subsequent regression during the onset of the Lameta period was slow and fluctuating. The oxygen isotope ratios of some limestones from the Kawant area (Mogra section, Nodular Limestone Formation) are unusually low probably due to thermal alteration effected by intrusion of the nearby Ambadongar Carbonatite at a later date.
Possible Lava Channels and Tubes from the Siwana Caldera Sequence, Siwana, Barmer District, Rajasthan
Authors: Bidwai Rajeev , Krishnamurthy P.
Published: November 2024

Lava propagating systems comprising channels and tubes from the Siwana caldera sequence of the Malani Igneous Suite are reported at Sain Ki Beri and Dhiran. Their location near the periphery of the ring dyke suggests that these channels may have been fed by the volcanic vents or cones, that were part of the ring which collapsed later.
Pattern and Intensity of Erosion in the Environmentally Stressed Khulgad Watershed, Kumaun Himalaya
Authors: Rawat J. S. , Rai S. P.
Published: November 2024

In the Khulgad watershed in the Kosi Valley in the Kumaun Himalaya, the average rate of erosion is 0.07 mm/year or 186 t/km2/year. Tectonic and anthropogenic activities have together appreciably accelerated the rate of erosion. A study over the period of three years (1991-1993) demonstrated that the rate of erosion is 0.19 mm/year (500 tlkm2/year) in the tectonically disturbed land, 0.12 mm/year (315 t/km2/year) in the barren land, and 0.10 mm/year (278 t/km2/year) in the agricultural land, while in the forest lands it varies between 0.02 mm/year (41 t/km2/year) under an oak forest and 0.04 mm/year (100 t/km2/year) under a pine forest. Compared to the intensity of erosion in the least disturbed oak forest, the erosion rate is about 10 times higher in the tectonically disturbed land, and 5 to 8 times higher in the anthropogenically stressed agricultural and barren lands.
Occurrence of Molybdenite in the Granites or Pirancheru near Hyderabad, Andhra Pradesh
Authors: Saxena Praveen Raj , Sudarshan V.
Published: November 2024

Paper reports a new occurrence of molybdenite in granite. X-Ray powder diffraction data for the identified mineral is provided.
Petrography, Mineralogy and Element Distribution in the Charmuria Limestone, Chhattisgarh Basin, M.P.
Authors: das Siddhartha Sankar , Rao C. N.
Published: November 2024

The Channuria limestone is characterized by grey-black colour, bedding structure, fine grain size and authigenic pyrite cubes. Petrographically a minimicrite, the rock exhibits a texture composed of dark crinkled and light coloured laminae of lime mud. Pyrite has discordant relationship with laminae, whereas silt-sized terrigenous particles are present in the interlaminar areas. Mineralogically the limestone is made up of low Mg-calcite and quartz. Trace element distribution tndicates that the original mineralogy at the time of deposition was calcitic in nature and its distribution in the rock was controlled by the depositional/diagenetic conditions as well as the detrital clastics supplied into the basin. The depositional environment of the limestone is interpreted as shallow marine lagoonal condition and the site of deposition was very near to shore. The dysaerobic to anaerobic condition which is attributable to the restricted circulation of water and the concomitant slow sedimentation rate were responsible for the development of authigenic pyrite and grey-black colour of the limestone.