bluuebunny/crossref_metadata_2025 huggingface dataset:
New Petrographic Data on the Metapelites of Almora Crystallines in Kumaun Himalaya
Authors: Karanth R. V.
Published: November 2024

Detailed structural and metamorphic study has revealed four tectonic episodes in the Almora Crystallines. The first two have brought major metamorphic changes. The earliest event (D1) belonging to the Late Precambrian/Early Palaeozoic orogeny produced the early cleavage (S1), parallel to the axial planes of isoclinal folds (F1) which now trend NNE-SSW. Almandine garnet and sporadically occurring staurolite generated during this pre-Himalayan orogenic event reveal a growth under static condition. D1 culminated with the intrusion of granitic lenses which granitised the adjacent metapelites. The second event (D2) belonging to the Early Tertiary Himalayan orogeny refolded this sequence into another set of isoclinal folds (F2) that are co-axial with F1 and produced widespread crenulation cleavage and snowball garnet. The continued action of D2 detached the crystallines from the root zone and pushed them over the less metamorphosed unit of the Lesser Himalaya as thrust sheet. Chlorite trails of the retrograded garnet in the intensely mylonitized zone indicate southeasterly movement of the thrust sheet. The early stage of thrusting of the nappe synchronized with the progressive metamorphism in the interior region. Third (D3) and fourth (D4) events merely folded and crinkled these rocks.
Multiple Deformation and Interference Structures in the Archaean Iron Ore Group Rocks Around Barda-Ulugutu Area, Singhbhum District, Bihar
Authors: Srivastava Deepak C. , Sarkar S. N.
Published: November 2024

Systematic structural analysis of the Archaean Iron Ore Group rocks around Barda and Ulugutu throws new light on the tectonic pattern and structural evolution of the area. The polyphase tectonics (D1-D3) is evident by the style and over-printing relationship between three types of s-planes (SO-S2), folds (F1-F3), and related lineations. Folds (F1) showing complex geometries, related lineations showing variable plunges and slaty cleavages (S1) have developed synchronously during the earliest tectonic phase (D1). The concomitant evolution of a new set of structures and deformation of preexisting D1 structures took place during the second phase (D2). The numerous smallscale culminations - depressions of F2 folds are attributed to the variable orientations of s-surfaces prior to F2 folding. Critical field evidences suggest the evolution of both F1 and F2 folds through similar deformational plans including buckling and post-buckle flattening. The concentric warps (F3) are envisaged to have developed under flexural conditions during D3 phase in local domains.

En-echelon arrangement of elliptical interference structures are ascribed to the nonorthogonal axial surfaces of F1 and F2 folds, and axial migrations during F2 folding. The co-existence of type-1 and type-2 patterns is due to F2-flexure of alternating tight and open folds (F1) within the same layer. That the bedding (sO) has been successively subjected to layer parallel compression is implied by buckling nature of repeated folding. Therefore, finite strain-ellipse of the whole area corresponds to constrictional field (1>?1>?2)
A Comparative Study of Tectonic Fabrics and Deformation Mechanisms in Dharwar Grits and Phyllites and Sargur Quartzites on the West of Chitradurga Supracrustal Belt, Karnataka
Authors: Chadwick B. , Ramakrishnan M. , Viswanatha M. N.
Published: November 2024

Late Archaean t ectonic LS fabrics in quartz-pebble conglomerates and grits in the lower part of the Dharwar Supergroup are defined by micas and the preferred planar orientation of long (X) and intermediate (Y) axes of ellipsoidal clasts of vein quartz. Long axes of clasts define the linear component ofthe fabric. With increasing strain the grits become L tectonites. Pressure solution and intragranular processes were important at lower strains, but dislocation creep was dominant at higher strains related to the LS fabric development.

Dharwar phyllites and polymict conglomerates have a bedding-parallel S fabric of phyllosilicates and detrital grains of quartz. This fabric is attributed to neocrystallization and recrystallization of phyllosilicates coplanar with a primary bedding-parallel fabric during diagenesis and subsequent burial and regional heating deep within the Dharwar volcanosedimentary pile. Coeval, domainal and penetrative tectonic LS fabrics, with transitions from domainal to penetrative types, which formed contemporaneously with LS fabrics in the grits were superimposed on the bedding-parallel fabrics. Microbuckling and pressure solution dominated early stages of the cleavage development, but they were overtaken by coplanar growth of biotite in the later stages. Discordant prisms of tourmaline and blue-green amphibole, radiating intergrowths of chlorite and quartz and octahedra of magnetite and their pseudomorphs of quartz indicate that grain growth took place during the low-grade metamorphism that outlasted the late Archaean deformation.

Transitional crenulation to penetrative S fabrics, locally with a linear component coaxial with folds, were superimposed on an older tectonic S fabric broadly parallel to bedding in the Sargur quartzites which form part of the basement immediately below the Dharwar Supergroup. The younger fabrics are correlated with the late Archaean tectonic fabrics in the Dharwar grits and phyllites. The older fabric, which includes prisms of kyanite, is believed to be related to pre-Dharwar deformation and medium- to high-grade metamorphism. Whilst microbuckling, pressure solution and dislocation deformation processes were important in the development of the younger fabric, their role in the development of the older fabric is not clear because of the superimposed effects of the later processes. Discordant chloritoid grown across pre-Dharwar garnet. staurolite and kyanite and their low-grade alteration products in the Sargur quartzites suggests grain growth took place during low-grade metamorphism that outlasted the development of the younger fabric, a relation identical to that in the Dharwar grits and phyllites.
Stratigraphic Status of Javanahalli Belt in the Archaean Geology of Karnataka
Authors: Ghosh Roy A. K. , Ramakrishnan M.
Published: November 2024

Javanahalli belt situated at the eastern margin of Chitradurga superbelt is either juxtaposed against the latter or separated from it by linear stripe of granite. The rocks of Chitradurga and Javanahalli belts and the associated enclaves are part of the Chitradurga Group. The primary lithologies of both the belts as well as the enclaves are comparable despite differences in metamorphic grade. These are ortho- and para-amphibolites, calc-silicate rocks, limestones, fuchsite quartzites, mica schists, cordierite-anthophyllite rocks and banded iron formation which is locally manganiferous. The meta-arkose/paragneiss, is mylonitic, potash-rich ortho-gneiss, and constitutes the deformed and partly remobilised basement. Preliminary structural studies have shown that Javanahalli belt is affected by early recumbent folds (F1) followed by the major second phase of nearly co-axial upright N-S folds (F2) which control the present map pattern. The ENE trending third phase open folds (F3) have caused local fold interference patterns. There is a progressive increase in metamorphism from west to east towards the gneissic contact, ranging from greenschist facies in Chitradurga belt to middle amphibolite facies in Javanahalli belt and enclaves, culminating in extensive granitic veining and migmatisation. Javanahalli belt represents a classic case of wide-spread basement reactivation associated with a boundary thrust in an ideal, ensialic, Archaean orogen.
Early Life in the Chitradurga Schist Belt
Authors: Suresh R.
Published: November 2024

The Archean Chitradurga schist belt (>2600 m.y.) is ideal for the investigation of morphological and chemical remnants of early life because of the presence of distinct sedimentary units. Available data so far, has not indicated the presence of undoubted microfossils from the Chitradurga belt. Possible microfossils from the Dodguni area are the only reliable evidences of early life from the Chitradurga schist belt.
Chemical and Magnetic Stratigraphy of Parts of Narmada Region, Deccan Basalt Province
Authors: Sreenivasa Rao M. , Ramasubba Reddy N. , Subbarao K. V. , Prasad C. V. R. K. , Radhakrishnamurty C.
Published: November 2024

Field investigations of a 666 m thick Deccan volcanic sequence north of the River Narmada (Khalghat-Mhow traverse; 60 km) showed the presence of 21 flows, while a 549 m thick southern section comprises of 28 flows (Mandaleswar-Pipaljopa traverse: 110 km). The lava sequences essentially consist of PI and/or Pyx phyric to aphyric basalts with glassy vesicular - amygdular tops/flow breccia.

On the basis of selected major and trace elements (Si, K, Ti, P, Ba, Sr, Zr), the Khalghat section is divided into three formations. The lowermost Narmada Formation is characterized by lower K, Ba, Sr, Ba/Ti, Ba/Sr and Ba/Zr than the succeeding Manpur Formation. The uppermost Mhow Formation is highly depleted in K, Ba, Sr compared to the two lower formations. Chemically, a four-unit informal stratigraphy has been adopted for the Mandaleswar section. The lower three may be correlated with the Narmada, Manpur and Mhow Fms of the Khalghat section and the upper one is labelled the Satpura Formation. Each formation is defined as a set of flows characterized by one or more chemical types such as 'primitive' and' evolved' ones.

The palaeomagnetic results of the Khalghat section demonstrate that the lower 254m pile of flows belongs to normal polarity (N) ('Narmada Normal Epoch') overlain by 412 m thick flows with reversed polarity (R) ('Malwa Reversed Epoch'). Interestingly, on the southern side of the river, about 21 m thick N flows are overlain by 476 m R flows, which in turn are capped by 52m thick N flows ('Satpura Normal Epoch') resulting in an unambiguous NRN sequence in the Deccan basalt province. It appears that the northern side of the Narmada River has been thrown up relative to the southern side. Based on the correlation of the magnetic reversals in the Deccan as well as marine magnetic anomalies, it seems likely that the normally magnetized older Rajmahal traps (about 100 MA) of eastern India form the base of the Deccan basalts.
On the Formation of K-Feldspar Augens - An Example from the Central Crystallines of the Bhutan Himalaya
Authors: Roy A.
Published: November 2024

Mesoscopic and microscopic studies on the K-feldspar augens of Thimphu augengneiss of Bhutan suggests microshearing followed by a rotational mechanism. Megacrysts of K-feldspar are often broken into smaller segments by ductile shear faulting, followed by a combination of simple shear and flattening deformation giving rise to the augens.
Reaction Textures in Silica-Deficient Granulites of Ganguvarpatti, Madurai District, Tamil Nadu
Authors: Mohan Anand
Published: November 2024

The silica-deficient granulites of Ganguvarpatti display textural evidences of metamorphic reactions, involved in the formation of diverse mineral assernblagest documented by different types of reaction coronas and symplectitic intergrowths. The symplectitic intergrowths, viz., orthopyroxene-spinel-cordierite and orthopyroxene-spinel-cordierite-sapphirine rimming corroded garnet have been attributed to reactions:

Gt + H2O⇋Opx + Sp + Cd

Gt + O2 + H2O⇋Opx + Sp + Cd + Sa

The textural relation of orthopyroxene isolated from sapphirine by a reaction corona of cordierite + spinet is related to reaction: Opx +Sa + H2O⇋Cd + Sp.
Gravity Bases Established by the Centre for Earth Science Studies in and Around Palghat Region, South India - Part I
Authors: Singh H. N. , Panchanathan P. V. , Unnikrishnan K. R.
Published: November 2024

Forty-one gravity bases were established with a Worden gravimeter in parts of Palghat gap area bordering Kerala and Tamil Nadu. The description of these base stations and the observed gravity values are presented. The observed gravity values at these stations are with reference to a value of 978.0715 gals at the Coimbatore Airport, established by the National Geophysical Research Institute, Hyderabad. The accuracy of the observed gravity values is estimated to be 0.07 mgal. The new base stations are being used for regional gravity surveys.
Occurrence and Significance of Algal Stromatolites from the Choral Valley, Near Barwah, Khargoan District, M.P.
Authors: Kale Vivek S.
Published: November 2024

Conophytoll cylindricus, Collenia columnaris, Collenia symmetrica and Collenia undosa are reported from the dolomitic intercalations within the Mehdikhera Chertbreccia Formation, exposed in the Choral river valley near Barwah, in Khargoan District, Madhya Pradesh. There is a lack of consensus regarding the origin of this Formation and it has been considered to be equivalent of Bijawars. The present report of stromatolites conclusively points to its sedimentary origin and suggests a need for a reappraisal of the age.
Progressive Charnockitization of a Leptynite-Khondalite Suite in Southern Kerala, India- Evidence for Formation of Charnockites Through Decrease in Fluid Pressure?
Authors: Srikantappa C. , Raith M. , Spiering B.
Published: November 2024

The crustal segment south of the Achankovil zone in southern Kerala is built up by two litho-tectonic units: The Nagerkoil unit is represented by a series of acid to intermediate magmatogenic gneisses and charnockites associated with layered anorthositic to noritic complexes. The Pon Mudi unit consists of interlayered garnet-biotite gneisses (leptynites), garnet-biotite-sil1imanite gneisses (khondalites) and garnet-biotite-sillimanite-cordierite metatexites which represent a series of intensely deformed psammitic and pelitic sediments metamorphosed to upper amphibolite grade (700-750°C; 6-8 k bars). Subsequent to regional metamorphism in the POD Mudi unit, the leptynites have been partly transformed to massive orthopyroxene-garnet-bearing charnockites along a conjugate set of fractures (s1: N30E ilDd s2: S70E) and the foliation planes of the rocks (N30-60W).

The geochemical data and the results of geothermobarometry show that charnockitization was essentialJy isochemical and occurred at 750 ± 50°C and 6 ± 1 kbars lithostatic pressure. A complex but conformable development of tbe fluid phase composition during metamorphism is indicated by the occurrence of at least four generations of fluid inclusions (almost pure H2O and CO2 inclusions, mixed CO2-H2O inclusions and CH4-N2 inclusions) in both the leptynites and the charnockites. The common presence of graphite+pyrrhotite+ilmenite furthermore suggests internal buffering of the fluid composition at oxygen fugacities below those defined by the quartz-magnetite-ferrohypersthene assemblage and XCO2>0.5.

The results of tbe present study indicate that charnockitization probably was not caused by the influx of CO2-rich fluids of deep-seated origin, tbe presently favoured model of granulite genesis (Newton, 1984), but rather was induced by an isothermal decrease of fluid pressure relative to lithostatic pressure, due to migration of the pore fluid into the network of fractures and ascent into higher crustal levels.
Trilobite and Other Trace Fossils from the Kunzam La Formation, Eastern Lahaul Valley, Himachal Himalaya
Authors: Bhargava O. N. , Srikantia S. V.
Published: November 2024

Trilobite locomotion trail Isopodichnus sp., swimming grazing trace Monomorphichnus sp. and resting trace Rusophycusdidymus are recorded from the siltstone-shale-quartzarenite sequence of the Kunzam La Formation (Cambrian) from the eastern Lahaul Valley, Himachal Himalaya. Besides these, a ringed conical ichnocoenosis is also reported.

The trilobite traces belong to Cruziana 'facies' which is characteristic of stable infra-littoral to circa-littoral zones. The presence of Rusophycus suggests a rather low energy environment.
40Ar-39Ar Darting of Deccan Basalts
Authors: Venkatesan T. R. , Pande K. , Gopalan K.
Published: November 2024

The feasibility of dating igneous rocks by the 40Ar-39Ar method in India using the Apsara nuclear reactor at BARC, Bombay is reported, based on measurements on two tholeiitic basalts and one alkali basalt associated with the Deccan volcanism. The ages of the tholeiitic basalts are 71±4 Ma and 65±4 Ma, respectively and that of the alkali basalt is 682 Ma. Apart from the low neutron flux requiring long irradiation times, the neutron fluence within the sample irradiation volume is somewhat anisotropic. The latter needs to be minimised to achieve the higher precision the method is capable of.
Chemical Ages of Zircons: New Results
Authors: Parthasarathy R. , Palrecha M. M. , Sankar Das M.
Published: November 2024

Seven zircon separates from different geological environments have been analysed for U, Th and Pb contents. U and Th are determined by Neutron Activation Analysis (NAA) and Pb by Differential Pulse Anodic Stripping Analysis (DPASV). The.elemental abundances have been utilised to calculate the chemical ages of zircons,
Carbon Isotope Ratio of the Coaly Matter from the Basal Part of the Proterozoic Vindhyan Supergroup
Authors: Krishnamurthy R. V. , Bhattacharya S. K. , Mathur S. M.
Published: November 2024

The stable carbon isotope ratio (13C/12C) of the carbonaceou matter from the basal part of the Vindhyan sub-group, estimated to be about 1200 Ma old, has been measured and the values support a biogenic origin for the incorporated carbon.
Isotopic Composition of Deccan and Ocean Ridge Basalts: Implications for their Mantle Sources
Authors: MacDougall J. D.
Published: November 2024

Isotopic data suggest that the mantle sources for ocean ridge basalts and some continental flood basalts, particularly the Deccan, may be in the same global depleted convecting mantle. If this is the case, the upwelling Deccan mantle source must have mixed with small amounts of an ancient enriched mantle component, similar to that detected in some kimberlites, prior to interaction with the crust. Such a scenario appears to be required by the facts that the isotopic composition of the depleted end members is approximately constant throughout the Deccan but different from ocean ridge basalts, and the oxygen isotopic composition of the most depleted Deccan sample is characteristic of mantle values. The wide variability in isotopic composition of Deccan and some other continental flood basalts is then the result of crustal processes, as has been suggested by many authors.
The Geochemistry of Uranium and Thorium Isotopes in the Salt Lakes and Adjacent Ground Waters of Rajasthan
Authors: Baskaran M. , Krishnaswami S. , Bhandari N.
Published: November 2024

The concentrations of 238U, 234Th and (234U238U) activity ratios and major ion chemistry of several water samples from the salt lakes and their adjacent ground waters in Rajasthan have been measured. 234Th concentration in all the samples, except in one high alkalinity water from the Sambhar Lake, are quite deficient relative to its parent 238U the average (234Th/238U)activity ratio being 0.12. This deficiency corresponds to a mean residence time of - 5 days for 234Th in these waters. In the high alkalinity water, 234Th concentration is at near equilibrium with 238U, yielding a residence time much longer than radioactive mean life. The long residence time of Th in high alkalinity waters may result from the complexing of 234Th by (CO3)-2 ion. 238U concentration in some of the ground waters near the salt Iakes are high, the highest being in a Didwana sample, 565 dpm/l, The Didwana samples also have the highest (234U238U) activity ratios observed for Indian waters. The high uranium concentration in the Didwana ground water is suggestive of uranium rich aquifer solids.
Mineral Chemistry and Petrology of the Manganese Silicate Rocks of Vizianagaram Manganese Belt, Andhra Pradesh
Authors: Bhattacharyya Samit
Published: November 2024

The manganese silicate-carbonate rock or manganese protore occurring asa conformable band within Khondalite Group of rocks, represents metamorphosed impure manganiferous sediments comprising manganese carbonate admixed with silica and clay. This manganese protore differs from gondite as well as kodurite and resembles queluzite and hence this protore is equated with the queluzite type. The significance of the presence of knebelite (manganese olivine) in the protore as an indicator of an original carbonate-bearing sediment has been discussed. Besides, mineralogy and chemistry of the various constituent minerals of the prot ore have been presented.
Geochemistry of feldspars from the Ambalavayal Molybdenite Prospect, Kerala
Authors: Santosh M.
Published: November 2024

Major and trace element geochemistry of coexisting alkali feldspar and plagioclase pairs from granite and alkali feldspars from the associated pegmatites of the Ambalavayal molybdenite prospect in Wynad district, Kerala, are presented. The element levels in both the feldspars show an overall comparability with the values reported from elsewhere. The nature of distribution of elements between coexisting feldspars is generally consistent with their crystal chemical behaviour. X-ray studies of alkali feldspars show a triclinic symmetry with the triclinicity values ranging from 0.2955 for feldspar from the granite to 0.6742 for feldspar from the pegmatite. Mol per cent feldspar end members range from Or56.43Ab40.52An3.05in alkali feldspar of the granite to Or74.00Ab22.51An3.19 in alkali feldspar of the pegmatite. The crystallization temperature of the alkali feldspar-plagioclase pairs in the granite is estimated to be between 704-740°C and that of alkali feldspar in the pegmatite to be between 525-580°C.
Soft-Seditnent Recumbent Folding in a Slump-Generated Bed in Jharia Basin, Eastern India
Authors: Ghosh S. K. , Mukhopadhyay Abhijit
Published: November 2024

Paraconglomerates, with pebble- or boulder-sized phenoclasts of laminated clay in a matrix of medium grained massive. sandstone, occur toward the top of a turbidite sequence in the Talchir Formation at the N. W. corner of the Jharia Coal Basin in eastern India. The soft-sediment folds within the shale phenoclasts are dominantly recumbent. An analysis of the geometry of the structures suggests that a mass of sand with interlayered clay units was liquefied or fluidized. This in its turn generated a plastic mass flow in the course of which tenacious clay yielded slabs which were subsequently rotated and deformed. When the down-slope movement of the sand body had slowed down or had come to rest on the basin floor, the piled up mass of soft sediments was flattened under its own load and the contortions of the clay phenoclasts acquired their recumbent character.
Proterozoic Basic Dyke Activity in Kerala Along the Western Continental Margin of India
Authors: Radhakrishna T. , Poornachandra Rao G. V. S. , Mitchell J. G. , Venkatesh A. S.
Published: November 2024

Palaeomagnetic data on the basic dyke rocks of Palachal (Cannanore district) and Agali (Palghat district) regions of Kerala in the southwestern part of India are presented. Palachal dyke has obtained stable vectors of D and I at 200Oe and possesses a single thermally discrete component with blocking temperatures at the Curie temperature of magnetite, whereas the Agali dyke has shown unstable behaviour to the AF and thermal demagnetisation tests. The Palachal dyke possesses a southwest negative NRM remanence (D = 225.5°; 1 = 48.5°; K = 48.52; α 95 = 7.24) and a pole position (44°N; 135°E) which is closer to that of Gwalior Traps (1830 ± 200m.y.) or Group IV dykes of Proterozoic age. K-Ar ages of 1668 ± 31 m.y. and 1660 ± 25m.y. have been obtained for the Palachal dyke and it is compatible with the Palaeomagnetic results. The basic dyke activity jn the southwest is not solely related to the rifting of western continental margin of India as earlier suggested but is in part of Proterozoic age.
Petrography and Geochemistry of the Tosham Hill Felsic Volcanics, Haryana
Authors: Pareek H. S.
Published: November 2024

Explosion breccia, tuff and felsite constitute the felsic volcanic rocks at Tosham Hill. Petrographically, the groundmass of tuff is distinct from that of felsite in being associated intimately with particles of iron ores. Geochemically, these rocks arc classified as potassic rhyolites and dacites. The trace elemental data show that explosion breccia is higher in Ba (230, 250ppm) than tuff and felsite (1O-60ppm); B(220ppm) and Sn (180 ppm) values predict significant economic concentrations of the latter at depth: quartz-porphyry dyke may perhaps be correlated with the Malani episode.
Geochemistry of the Archaean Gneiss Complex and Associated Rocks of the Kanakapura Area, Karnataka, South India
Authors: Mahabaleswar B. , Vasant Kumar I. R. , Friend C. R. L.
Published: November 2024

The area of present investigation forms a part of the Archaean high-grade gneiss terrain of Karnataka. The rocks comprise both acid and basic lithologies and involve the late Archaean Closepet granite. Petrographically the acid rocks span the range, tonalite to granite, whilst the basic rocks are amphibolites and two-pyroxene granulites. The acid 'rocks have calc-alkaline affinities and resemble those from the transition zone to the east. Trace elements show them to be relatively undepleted with K/Rb ratios of >500. Simulated REE patterns of gneisses reveal that there are three broad groups: two of which are steep, but at different REE abundances, suggesting high pressure evolution; and one relatively flat group suggesting low pressure evolution. The basic rocks have a tholeiitic affinity, but are clearly separate, the granulite facies types being slightly more magnesian. The trace element chemistry of these basic rocks has been disturbed by migmatization. The REE patterns of Closepet granite are steep and may be related to the partitioning of accessory minerals such as allanite. An attempt is made to establish the relative position of the granulite facies metamorphism with respect to the regional fabric and retrogression.
Marine Magnetic Profiles from the Direction Bank to the Kori Bank, Western Continental Shelf of India
Authors: Ramana M. V. , Subrahmanyam V. , Subba Raju L. V.
Published: November 2024

Total magnetic field intensity measurements along two parallel NW-SE tracks from the Direction Bank to the Kori Bank show correlatable magnetic anomalies. High frequency positive anomalies observed northwest of Kathiawar coast terminating at about 21°N are interpreted due to the magnetic basement i.e, basalts at a depth of about 2 km. A low amplitude negative anomaly observed around 21°N (between 69°E and 70°E) may be due to the westward extension of the Narmada-Son lineament. Absence of significant anomalies south of these high frequency anomalies may be due to thin Traps or greater thickness of sediments. High amplitude and broad wavelength negative anomaly observed off Bombay (l9°N, 71.5°E) is interpreted as due to contact or faulting of Precambrian formations and Deccan Traps.
A Parametric Approach to Terrain Analysis and Geomorphic Regionalization of Pravara River Basin (Maharashtra)
Authors: Kale Vishwas S. , Rajaguru S. N.
Published: November 2024

A detailed micro-level statistical analysis has brought out the spatial variation in the terrain of Pravara and Mula sub-basins. Principal component analysis has aided in establishing three groups of inter-related variables; and the Factor Analysis has been able to synthesize patterns of six geomorphic variables into a single comprehensive pattern labelled as 'Morphogenetic Regions'. The multivariate analysis has been able to derive equations of high predictive and descriptive value. Such an approach to terrain analysis has been found to be very fruitful than the conventional morphometric analysis.
Granite Rock Standard Sample: NGRI-G
Authors: Govil P. K. , Ahmad S. M.
Published: November 2024

As a part of standard rock sample preparation program, NGRI has prepared a standard rock sample of granite for chemical analysis of granite rock samples using instrumental methods of analysis and to calibrate the instruments. International granite rock standards prepared by United States Geological Survey are no available and, thererore, it was felt necessary to prepare our own standards for different rock types.

The sample is homogeneous and gives reproducible values for all the major and minor oxides and ten trace elements. Replicate analysis at NGRI using XRF, AAS, Spectrophotometer and at other laboratories in USA and West Germany have given confident results. Proposed values for nine oxides and seven trace elements are given in this paper and the sample is offered to be used as a geochemical reference standard for granite samples.
Trends in Grain-Size Measures of the Quaternary Sediments off the Vengurla Coast, Maharashtra; With Reference to Beach Morphology and Tectonic Evolution
Authors: Sukhtankar R. K.
Published: November 2024

Field studies along the coast of Vengurla, Maharashtra, reveal presence of stabilised dunes, older and younger raised beaches apart from the present intertidal zone. From these geomorphic features, a fall in sea-level to the extent of about 4 m and 1 m during the Holocene period is suggested.

The sediments constituting these geomorphic features have been examined for their grain-size characteristics. Statistical parameters, such as: mean size, standard deviation and skewness have been compared from each geomorphic unit. The comparison indicates reversals in their trends of variation, which have been ascribed to transgressional cycles.

It is suggested that tectonic control, which operated either through a relative fall in sea-level or an emergence of the Indian shield during the Holocene period is responsible for the accretionary nature of the beach.
Birmania Phosphorites: Petro-Mineralogical Characters and Palaeogeological Implications
Authors: Husain Viqar , Banerjee D. M.
Published: November 2024

The lower Palaeozoic (possibly Cambrian) phosphorites of Birmania in Western Rajasthan are pelletal as well as microcrystalline. Carbonate fluorapatite is the only mineral phase in these phosphorites. Petrodiagenetic and mineralogical studies indicate primary precipitation of apatite directly from the basinal waters. Suggestions have been made for an extensive Cambrian sea encompassing the phosphogenic provinces of Western Rajasthan, Hazara in Pakistan and Mussoorie hills of Kumaun Himalayas.
Petrogenesis of the Angadimogar Syenite, Kerala and its Taphrogenic Affiliation
Authors: Santosh M. , Nair N. G. K.
Published: November 2024

A syenite pluton occurring ncar Angadimogar in Cannanore district. northern Kerala and emplaced close to the continental margin and along a NW-SE trending faultlineament is reported. Alkali feldspar constitutes the dominant mineral with subordinate albitic plagioclase and quartz. corresponding to nordmarkitic composition. The syenite shows unique assemblage of accessory minerals. namely hornblende, riebeckite. crocidolite and acmite with diopside, bi.otite. zircon, sphene and calcite. High alkali content, with dominance of Na20 over K20, moderate transition dement contents and low Rb values are characteristic. Petrochemical features suggest melt equilibration from a K-rich, Rb-depleted mantle source, with subsequent amphibole and alkali feldspar fractionation. Significant increase in fO2, fH2O and peralkalinity towards the residual stage is deduced. The syenite belongs to the group of Late Precambrian-Early Palaeozoic alkaline intrusives of the region, with its generation and emplacement correlatable with the taphrogenesis of the western continental margin of lndia.
Late Miocene Planktonic Foraminifera of Interview Island, Bay of Bengal
Authors: Sharma V. , Kumar Ravindra
Published: November 2024

A sequence of clayey to sandy limestone exposed on the eastern coast of Interview Island, Bay of Bengal is studied for foraminiferal content. Twenty-seven species of planktonic foraminifera are reported. The species assemblage consisting of Globorotalia plesiotumida, Globigerinoides extremus, Neogloboquadrina acostaensis and Globorotalia (Tenuitella) anfracta suggests a Late Miocene age for the limestone unit. The assemblage is referable to Zone 17 of Blow (1969) and Zone 17A of Srinivasan and Kennett (1983) and represents the Neillian Stage (Srinivasan, 1978).
Tectonically-Controlled Gold Mineralisation in Chigargunta Area, South Kolar Schist Belt, Chittoor District, Andhra Pradesh
Authors: Mukherjee M. M. , Natarajan W. K. , Shashidharan K.
Published: November 2024

Several parallel to sub-parallel auriferous mineralised zones of economic significance occur over a strike length of 3 km and spread over a width of about 1 km in 'Chigargunta area of South Kolar schist belt. The host rocks for mineralisation are metamorphosed basalt and acid tuff ('Champion gneiss'). The mineralised zones represent ductile shear zones transecting the regional north-south trending schistosity (S2) at low angle. The pre-existing planar and linear fabrics of the rocks have been rotated into parallelism with the shear zone. The shear zones display mylonitic foliation with prominent downdip lineation, folds of variable orientation, boudinaging and crenulations. Such deformation features are confined only to these strongly tectonised zones believed to have evolved by simple shear deformation. A progressive grain size reduction accompanied by hydrothermal retrogressive metamorphism of the amphibolite facies host rocks culminates laterally into the centre of the mineralised zones with lower grade greenschist assemblage. Nondilatant pegmatite veins and some high temperature alteration minerals indicate possible strain heating. The auriferous lodes occurring in Kolar Gold Field might have a simiiar tectonic evolution.
Argentiferous Roquesite (CUInS2) From the Tosham Tin Prospect, Bhiwani District, Haryana
Authors: Seetharam R.
Published: November 2024

The sheared rhyolite-metasediment contact of the Tosham Hill is well-mineralised with disseminations and thin veins of very fine grained pyrite, pyrrhotite, chalcopyrite, sphalerite, galena, cassiterite, stannite, bismuthinite, rutile, hematite, wolframite and roquesite. Roquesite occurs intimately associated with chalcopyrite and is replacing it. The approximate reflectance of roquesite in white light measured in air was 20.7% and its average Vickers microhardness value was 229. Qualitative analysis of roquesite carried out with the help of the Laser microanalyser showed presence of major amounts of copper and indium and minor amount of silver. Based on the physical, optical and micro-chemical data, roquesite has been identified as the argentiferous variety, This is the first report of the occurrence of roquesite from India.
Hydrogeomorphic Classification of the Marginal Gangetic Alluvial Plain in Uttar Pradesh, India, Using Satellite Imageries
Authors: Bajpai V. N. , Gokhale K. V. G. K.
Published: November 2024

On the basis of multispectral analysis of LANDSAT imageries, the Marginal Gangetic Alluvial plain has been lithologically and geomorphologically classified. Distinct morphological divisions mapped include, uplands, ravines, floodlplains and rocky tracts. The upland morphology is typically represented by the cis- and transregions of the Ganga and Yamuna rivers. The ravines have characteristic patterns and reflect distinctly the influence of soil texture, basement structure and relief. While dendritic patterns are common in areas with shallow basement indicating limited infiltration, irregular pattern of deep headward erosion are common in areas of high relief. The flood plains formed by rivers of the Ganga and Yamuna system exhibit variations in morphology corresponding to the variations in the sediment load and grain size. The rocky tract is typical of flat-topped ridges and escarpments with sporadic alluvial patches.

Abandoned channels, intersecting ridges controlled by joints and depressions filled with alluvium within the rocky tract, which offer potential sites for ground water development have been identified.
Mineralogy and Mineral Chemistry of the Manganese-Poor and Manganiferous Iron-Formations from the High-Grade Metamorphic Terrain of Southern Karnataka, India
Authors: Devaraju T. C. , Laajoki K.
Published: November 2024

The iron-formations of the high-grade metamorphic terrain of Southern Karnataka comprise both Mn-poor (av. 0.3% MnO) and Mn-rich (av, 7.4% MnO) types. The two types are distributed throughout the 1273km2 area studied. Each type occurs constituting a large proportion of an individual body and within each body, complex variations from one type to the other, both along and across the strike, might exist. Despite their high-grade metamorphism the rocks have preserved primary sedimentary banding; there are, however, no relics of original textures or minerals. A very striking mineralogical feature of these iron-formations is the common occurrence of pyroxenes and garnets as major mineral phases in addition to magnetite and quartz. Mn-rich types are typically enriched in garnet whereas the Mn-poor types are generally almost devoid of it or contain' a small proportions of it. Pyroxenoids appear in the Mn-rich iron-formation analysing over 6% MnO. The other minerals of restricted occurrence include ferroactinolite, grunerite, Ksfeldspar (orthoclase-microcline), plagioclase (An 20-25), olivine, biotite and chlorite. Apatite is the most common accessory; zircon is scarce.

A detailed electronprobe microanalysis has revealed; (1) the low MnO content of less than 2%,1%,0.4% and 0.03% respectively, of garnet (70-81% almandine), orthopyroxene (ferrohypersthene-eulite ; 30-22 En), clinopyroxene (augite-ferroaugite to saliteferrosalite) and magnetite in the Mn-poor iron-formation, (2) the high MnO content of 10-20.5%, 2.5 to 15%, 2.25 7.5 and 0.2-0.3% respectively of garnet (almandine 30-54 - spessartite 39-49), orthopyroxene (manganoan ferrohypersthene-rnanganoan eulite), clinopyroxene (manganoan augite-ferroaugite to manganoan salite-ferrosalite) and magnetite in the Ma-rich iron-formation, (3) the occurrence of pyroxenoids varying in character from pyroxferroite to pyroxmangite with the Fe: Mn ratios either just below or above 1 : 1, (4) the common occurrence of (exsolution) intergrowths of one pyroxene in the other, (5) the occurrence of Mn-poor magnetite (≤0.03%MnO) carrying abundant exsolutions of hercynite and Mn-poor (around 1% MnO), ilmenite in the Mn-poor iron-formation and (6) magnetites (around 0.3% MnO) carrying Mn-rich ilmenite (MnO 15-30%) exsolutions in the Mn-rich iron-formation. An empirical study of the Mg-Fe-Mn distribution in the co-existing pyroxene and garnet has shown that these have crystallised in equilibrium metamorphic conditions corresponding to granulite facies. Estimations based on better suited pyroxene-garnet compositions occurring in the associated granulite facies rocks have indicated the formation of ironformations of the area at temperatures of 720-820°C and pressures of 7-11 Kbars.
Mineral Composition, Textures and Deformation in Late Archaean Banded Iron-Formation Rich in Magnesioriebeckite and Aegirine, Bababudan, Karnataka, Southern India
Authors: Chadwick B. , Garrioch N. H. G. , Ramakrishnan M. , Viswanatha M. N.
Published: November 2024

Assemblages rich in magnesioriebeckite, aegirine and magnesian siderite (var. pistomesite) characterise parts of the Banded Iron-Formation low in the Mulaingiri Formation of Bababudan, Electron microprobe analyses show that aegirine contains up to 53.29 wt% Si02, 0.17 wt% A1203, 32.20 wt% TotFeO, 0.23 wt% MgO and 14.09 wt% Na20; and magnesioriebeckite contains up to 55.57 wt% Si02, 0.07 wt% Al103, 29.16 wt% TotFeO, 8.53 wt% MgO and 7.37 wt% Na20. These abundances are broadly in accord with previously published results from wet analytical techniques.

A diagenetic or very low-grade metamorphic texture of randomly oriented needles of magnesioriebeckite and granoblastic-polygonal quartz in chert mesobands is transitional into a texture dominated by long prisms of magnesioriebeckite intergrown with elongate grains of quartz which forms an LS tectonic fabric. Aegirine and magnesian siderite have locally replaced magnesioriebeckite in this fabric. The carbonate also forms small ring structures, interpreted as deformation phenomena, in parts of some mesobands.

The pre- and syntectonic textures of magnesioriebeckite are regarded as the products of percolating solutions rich in Na+ and Mg++ interacting with the host during diagenesis, very low-grade burial metamorphism and progressive deformation. The tectonic LS fabric appears to have been initiated early during deformation with textural modifications taking place during buckle shortening and layer-parallel shearing.
A Note on the Auriferous Banded Iron-Formation of Kolar Schist Belt
Authors: Natarajan W. K. , Mukherjee M. M.
Published: November 2024

Banded Iron-Formation (BIF) comprising quartz, pyrrhotite/grunerite-actinolite and quartz, magnetitejgrunerite-actinolite occurs widely in Kolar schist belt as narrow (0.5 rom to few tens of metres wide) interbeds within the metamorphosed basic volcanic and acid volcanogenic rocks (' Champion gneiss '). All gradations between these two end members render the BIF bands heterogeneous in composition. The sulphidic BIF horizons occurring near the western margin of the schist belt in association with pillowed metabasaJts are persistent along strike for several kiJometres and are auriferous at places. The BIF horizons occurring towards the eastern margin of the schist belt are narrower) impersistent in strike and are not known to contain gold mineralization.

Two types of mineralization have been recognised in BIF. In sulphide facies BIF, native gold occurs in arsenopyrite which along with pyrrhotite and amphiboles form massive layers alternating with quartz. Here the auriferous sulphide layers are primary, subsequently modified by metamorphism and deformation. In the second type, gold mineralization is confined to syntectonic quartz veins in the sulphidic BIF. A volcanogenic model for the precipitation of auriferous BIF is favoured.
The Cycling Redox State of Iron in the Genesis of Banded Iron-Formations and their Associated Enrichment Iron Ores
Authors: Morris R. C.
Published: November 2024

A simplified eclectic model for the genesis of Banded Iron-Formation (BIF) and associated iron ores in the Hamersley Group of Western Australia can be applied with suitable modifications to comparable situations elsewhere.

BIF was deposited from upwelling ocean currents as a chemical sediment in a platformal environment. Ferrous iron and silica were supplied to seawater by direct input from rivers and sediment-seawater reactions, forming a general background level which was periodically supplemented by exhalative components from major submarine'hot spot' activity. Iron was precipitated largely by photo-oxidation of ferrous iron as it reached the surface rather than by a more commonly advocated biochemical process. During early diagenesis ferrous minerals, such as magnetite, were formed.

Following consolidation, folding and exposure, supergene enrichment occurred in suitable hydrodynamic systems enabling deep ores to form in the BIF while the surface eroded. The enrichment in these small artesian systems was controlled by large electrochemical cells driven by oxygen reactions in the outcrop. This allowed ferrous to ferric reactions to occur at depths well beyond the reach of atmospheric oxygen. Burial and subsequent metamorphism of such goethite-rich deposits, particularly those formed during the Precambrian, resulted in the development of hematite-rich ores. Some of these have been thermally metamorphosed by igneous intrusions to give magnetite-rich deposits. Later re-exposure has further modified the ores by leaching, oxidation, dehydration and surface lateritisation.

Ores formed during later periods are generally unmetamorphosed and retain their goethite-rich character. These have been modified by continuing exposure and are commonly strongly leached.
Loess Deposits of Kashmir, Northwest Himalaya, India
Authors: Pant R. K. , Dilli K.
Published: November 2024

The spatial and temporal variation of Kashmir loess deposits has been explained as the function of palaeotopographical configuration consequent to the Pir Panjal Range uplift datable at 0.4 m.y. At least three palaeosurfaces were available for loess deposition at different time intervals. Three types of loess-palaeosol profiles developed on these palaeosurfaces which show altitudinal differences. Stratigraphical correlation between different profiles was possible with the help of marker beds and soil typological parameters. Seven lithounits constitute the total loess-palaeosol succession in the basin. Soil types were recognised using sedimentological, mineralogical and microfabric parameters in addition to field criteria.
Charnockite 'in the Breaking': Evidences from the Trivandrum Region, South Kerala
Authors: Santosh M. , Yoshida Marasu
Published: November 2024

Field and microstructural evidences indicating retrogressive-transformation of banded charnockite to leptynite (garnet gneiss) through a transition zone of khondalite (garnet biotite gneiss) is reported from two localities in south Kerala. In the same localities, formation of acid charnockite patches are also noted. Structural analyses show that the breaking event post-dates the formation and isoclinal folding of banded charnockite, but clearly pre-dates the making of patchy charnockite.
Crenulation Cleavage in Slate of the Chamba Syncline: Associated Microstructures and Origin
Authors: Singh Keser , Thakur V. C.
Published: November 2024

The microstructures associated with the crenulation cleavage in the slates of the Chamba Syncline, Western Himalaya, indicate that metamorphic differentiation following differential plastic flattening and fracturing is largely responsible for its origin. The stress gradient leads to migration of soluble minerals like quartz and calcite from limbs to hinge regions of microfolds as a result of pressure solution leaving behind micarich bands (insoluble) defining the crenulation cleavage.
Scanning Electron Microscopy Study of the Quartz Overgrowths Within Neogene Sandstones of Bengal Basin, Bangladesh
Authors: Imam Md. Badrul
Published: November 2024

Scanning electron microscopy study reveals successive stages of quartz overgrowth development during post depositional burial diagenesis in the Neogene sandstones of the Bengal Basin. The quartz overgrowths are most abundant and form major cement in Bhuban sandstones, are less common in Bokabil sandstones, While they are rare in Tipam sandstones. The growth of authigenic quartz proceeds from initial incipient and isolated quartz crystals to advance-terminated and euhedral quartz overgrowth completely engulfing the host detrital grain - the latter being formed by mergence of the incipient quartz units into a single unit. Mutual interlocking of adjacent quartz overgrowths of advance stage frequently produce sutured type contact that may be mistaken as pressure solution under optical petrographic studies. Development of quartz overgrowths is inhibited or retarded by the presence of thick authigenic chlorite rims around detrital grains. Two most important sources of quartz overgrowths are the pressure solution and the smectite to illite diagenesis in illite/smectite mixed layer clay mineral in the interbedded shales.
Garnet + 2 Sillimanite = 3 mg-Spinel + 5 Quartz Equilibrium-A Potential Geobarometer
Authors: Bhattacharya A. , Mazumdar A. C.
Published: November 2024

A geobarometer based on the equilibrium Mg3Al2Si3O12 + 2Al2SiO5 (sillimanite) = 3MgAl2O4+5SiO2 has been proposed. The geobarometric expression can be stated as P(bar)=9.68 T - 7106 + 10.307 T In (agarnetMg3Al2Si3O12)1/3/(aspinelMgAl2O4). Application of the proposed geobarometric formulation to some metapelites indicates that it registers reasonable pressure values which are in good agreement with the recommended pressure values for different terranes.