bluuebunny/crossref_metadata_2025 huggingface dataset:
Pelitlc Hornfels Xenoliths in the Garnetiferous Granulites and Granitlc Rocks of the Kondavidu Area, Guntur District, Andhra Pradesh
Authors: Sadashiyatah M. S. , Subbarayudu G. V.
Published: November 2024

The geological setting, petrography and petrochemistry of the pelitic hornfels xenoliths of the Kondavidu area and the mineral transformations observed in them form the subject of this account. Based on mineralogy, the hornfelses have been classified into six types, and the minerals found in these types are garnet, andalusite, sillimanite, cordierite, corundum, anthophyllite and spinel. The instability of the almandine garnet of the composition Alm69+5 Py25+9 Sp2+3 And2+3 found in the pelitic hornfels is a dominant feature and it is attributed to the superimposition of thermal metamorpnism over regionally metamorphosed pelitic rocks in which the garnet is a stable mineral.

The mineralogical transformations, especially, the breakdown of almandine garnet to aggregates of cordierite, corundum, spinel and magnetite, and the formation of pseudomorphs of cordierite after garnet are attributed to the Oxidation of the garnet. The formation of fibrolite from cordierite, garnet, anthophyllite, corundum and even from potash felspar is due to metasomatism of alumina-rich solutions associated with the later injection metamorphism.

The chemical data indicate that the hornfelses are pelitic in composition and they belong to the pyroxene hornfels facies of contact metamorphism. The pelitic hornfelses owe their origin to the thermal metamorphism of the regionally metamorphosed pejites by the parent magma of the intermediate charnockites.
Cluster Analysis Approach to the Problem of Facies Classification of the Carbonate Rocks in the Krol Series
Authors: Gundu Rao C.
Published: November 2024

The Krol series in the Sub-Himalayas, include six lithological units, namely Infra Krol, Krol A.B.C.D. and E. Among these, A.C.D. and E. incorporate increasing thicknesses of carbonate rocks from A to E, with minor shale intercalations. Cluster analysis of 150 carbonate samples drawn from these four formations in five stratigraphic profiles between Mussoorie and Lansdowne, based on six petrographic attributes, has shown that the samples cluster into four meaningful groups. Interpretation of these groups reveals that the carbonate rocks of the Krol series fall into two broad facies or depositional mechanisms, one Krol A+C, of micrites and sparites, and the other, Krol D+E of calcicdolo and dolocalcicmicrites, and their variants. The earlier classification of Krol carbonates into four lithological units, A.C.D and E, from a facies point of view, seems to be unjustified. The depositional mechanism of A+C is succeeded by Krol D+E in the vertical profile. This supports the earlier view of Rao that the Krols represent a phase in the development of a basin centre evaporite sequence.
Petrochemistry of a Hornblende Porphyrite from Chityal, Andhra Pradesh
Authors: Soma Yajulu P. V. , Reddy M. N.
Published: November 2024

An isolated oval body of hornblende porphyrite occurring three km SE of Chityal, Nalgonda District, A.P. shows typical porphyritic texture both megascopically and microscopically. Euhedral primary hornblende occurs as pnenocrysts in a mesostasis of secondary actinolite and altered plagioclase. With the development of diopside at the expense of hornblende, the rock has acquired a granulitic texture while retaining the porphyritic habit.

Chemically the rock is characterised by low alumina and high magnesia and calcium. Among the trace elements, the high concentration of Cr, Cu, V and Co are in sympathetic relation with the major elements. The somewhat high values of Li, Sr and Rb, are thought to be partly due to introduction through water-enriched magmatic fluids which have metamorphosed the primary members of the rock. Tne rock appears to have suffered first a retrograde and then a prograde metamorphism.
Metamorphic Belts in Singhbhum, Manbhum and Chhota Nagpur, E. India
Authors: Ray S. , Gangopadhyay P. K.
Published: November 2024

Earlier studies on metamorphic zones in the metamorphic belts of Singhbhum, Manbhum and adjoining parts of Chhota Nagpur around longitude 86°E and between latitudes 22°45 Nand 23°40 N have been synthesised. Maps of Barrovian zones delineated by different workers in small areas have been coordinated into a regional zonal map.

Broad structural data of earlier workers plotted on the map depict that the pattern of extension of the zones over the whole region has a direct correlation with the plunges of the regional fold axes; higher grade zones occupy anticlinal cores with the lower grade ones succeeding them in the direction of the stratigraphic younging.

Granites, late syntectonic with tbe major folds on S" accompany most sillimanite zone outcrops. Andalusite occurs (i) across the chlorite to the kyanite zones along the southern fringes of the Dalma basic volcanics, and (ii) also sporadically. within sillimanite zone schists in association with sillimanite and kyanite.
Copper Mineralisation in the Bijawar Series Around Sonrai, District Jhansi, U. P
Authors: Singh K. K. , Goyal R. S.
Published: November 2024

The carbonate members of the Bijawar series (Precambrian) which are faulted against the Bundelkhand granites, show copper mineralisation at several localities between Sonrai and Tori. The ore bodies are highly oxidised and are chiefly localised along the fault and shear zones. Both primary and secondary wall rock alterations have been observed. Chalcocite, cuprite and malachite are the main copper ore minerals, with minor amounts of covellite, tenorite and chalcopyrite. Goethite along with malachite forms the conspicuous mineralogical guide for prospecting on the surface. The present surface studies indicate that the copper mineralisation is epigenetic and suffered deep oxidation along weak zones. The possibility of supergene sulphide enrichment is poor due to presence of reactive carbonate wall rork.
Karstic Limestones in Parts of Raipur District, Madhya Pradesh and their Groundwater Possibilities
Authors: Adyalkar P. G. , Phadtare P. N.
Published: November 2024

The southernmost parts of the Raipur district, covering about 5,600 sq km of area between the north latitudes 20°30' and 21°30' and the east longitudes 81°30' and 82°15' and forming part of the extensive saucer-shaped Raipur basin of the Chhattisgarh region of Madhya Pradesh, has been studied by systematic geohydrological work.

The limestones of the area have high secondary permeability and are observed to be rich in groundwater potential. The large vertical thickness and considerable lateral extension of carbonate rock aquifers indicate scope for development of groundwater.
Mineralogy and Origin of the Rajahuan Bauxite Deposits, Uttar Pradesh, India
Authors: Swarup Prem
Published: November 2024

Deposits of bauxite were discovered by the Directorate of Geology & Mining, U.P. on the bed rock of Upper Vindhyan sandstone at Rajahuan, district Banda, Uttar Pradesh in the year 1965. This paper deals with the mineralogical studies done on the laterite profile of Rajahuan with the help of X-ray diffraction method. A brief description of the members of the profile along with the development and distribution of chemical constituents and minerals is given. In the bauxite, gibbsite is the chief mineral with subordinate boehmite, sometimes with minor diaspore. Anatase is fairly high. On the basis of field and laboratory data it is concluded that the Rajahuan laterite profile represents an in-situ residuum formed in a regular weathering profile with the bauxite forming in the zone of aeration, which is underlain by cavernous laterite developed in the zone of fluctuation of water table, and the basal lithomarge formed within the zone of saturation. It is suggested that the parent rocks of this residuum were a sandstone-shale sequence.
Time-Relation of Poly Metamorphic Recrystallisation in the Precambrian Rocks of the Sonapet Valley, Eastern India
Authors: Bhattacharyya D. S.
Published: November 2024

Three phases of high grade metamorphism are recognised here. These are dated with reference to the four phases of deformation recognised in this area. It is concluded that the index minerals are progressive in time and space; the metamorphisms are also synkinematic to post-kinematic. Zonal patterns are analysed and it is seen that these show synchronous fold shapes. Folding of the geoisothermals seems to be the best explanation for the metamorphic episodes.
Copper Mineralisation in Karnataka, India
Authors: Radhakrishna B. P.
Published: November 2024

The known occurrences of copper ore in Karnataka are grouped under five main groups (1) those associated with ultrabasic complexes (2) those associated with quartzites and quartz schists of Lower Dharwars (3) those associated with shear zones in the greenstone schists-volcanic assemblages comprising pillow lavas, agglomerates and tuffs (4) hydrothermal lode deposits and (5) those associated with major fault zones.

Targets for further search for copper are indicated to be the layered ultrabasic complexes, quartzitic sediments of Lower Dharwars, shear zones in submarine volcanic assemblages of andesitic composition, metamorphosed shales and graphitic schists, brecciated and mylonitized zones associated with major faults of great horizontal and vertical extent.
Tipam Group in the Subsurface of Upper Assam Valley, South of Brahmaputra
Authors: Shrivastava P. K. , Ganeshan S. , Ray D.
Published: November 2024

The Tipam group in the subsurface of Upper Assam valley is discussed in this paper. The group is divisible into four formations in'ascending order: the Geleki sandstone, the Lakwa clay, the Nazira sandstone, and the Girujan clay. Within the Geleki sandstone a basal member, the Safrai, and Teok sandstone member within the Girujan clay are mappable. These rock-stratigraphic units are systematically described. The group unconformably overlies the Barail group, and is overlain unconformably by the Namsang formation. The problem of the Surma group in the area is discussed and it is concluded that this group is not developed here. Its age equivalents form a part of the Geleki sandstone. The age of the Tipam group ranges from Middle Miocene to Pliocene. The present subcrop Tipam rocks were formed by fluvial processes in an intermountain continental basin. Commercial accumulation of oil in these rocks and older formations has fed to extensive deep drilling which provided data for the present study.
Structural History of the Saladipura Pyrite-Pyrrhotite Deposit and Associated Rocks, Khetri Copper Belt, Rajasthan
Authors: Ray Sumit Kumar
Published: November 2024

Elucidation of the structural geometry and structural history of the area around Saladipura in the southern part of the Khetri copper belt, Rajasthan, helps in precise dating of formation of the massive sulphide deposit with respect to the different phases of deformation affecting the area. The pyrite-pyrrhotite deposit of Saladipura occurs almost along the contact of two lithological units and is traceable over a strike length of about 7 km. Rocks of the Delhi group exposed in this area have been folded into a series of normal, upright to inclined folds F1 with NE-SW trend. Formation of sulphides in the area can be dated to be earlier than the first recognisable phase of deformation F1 folding. Sulphides of the ore body bear imprints of all the phases of deformation affecting the associated metasediments of the Delhi group and distribution of sulphides within the ore body often define stratification. All these evidences indicate syngenetic primary nature of the sulphides, which have undergone textural modification, mineralogical reconstruction and (re)mobilisation in the course of regional metamorphism and deformation.
Geochemistry and Origin of the Peninsular Gneisses of Karnataka, India
Authors: Divakara Rao V. , Naqvi S. M. , Satyanarayana K. , Hussain S. M.
Published: November 2024

Major and trace element analyses of gneisses from parts of the Karnataka State, reveal heterogeneity in their chemical, modal and normative compositions. On the basis of chemical differences it is suggested that the parent material for these gneisses was pelitic/arkosic in nature. Heterogeneity in their composition is attributed to their age difference, degree of granitisation and migmatisation to which the pelitic/arkosic parent material was subjected.
Quantitative Evaluation of Bouguer Anomalies in Puranpur Area of the Ganga Basin
Authors: Datta A. N. , Trehan D. K. , Choudhury S. K.
Published: November 2024

Bouguer gravity data of the Ganga basin could not be interpreted earlier quantitatively, as it was believed that the isostatic effect of the Himalayas masked all the local anomalies. The present work, however, suggests that the contribution of substantially thick low density post-unconformity sediments is more in masking the local anomalies than the isostatic effect.

The gravity data in Puranpur area of the Ganga basin have been interpreted in terms of basement depths after removal of the effect of the post-unconformity sediments, whose disposition is fairly well known from the seismic data. In the Puranpur depression the maximum sedimentary thickness is about 6000 metres. The pre-unconformity sediments in this depression may be different from those in the adjoining areas, to the west and south. The northeastern limit of this depression is a basement ridge on which interesting structural features are located.

In the northern part of the area the basement structures exhibit a WNW-ESE trend indicating that this area probably belongs to the Krol basin. In the southern part, the trend is dominantly E-W, but is disturbed by a number of NE-SW trending features. The former is probably governed by the basement rocks belonging to the Bundelkhand massif while the latter are due to the continuance of the Aravalli trend of the peninsular area.
Geochemistry of the Precambrian Alkaline Rocks and Carbonatites of India-Gaps in our Knowledge
Authors: Sethna S. F.
Published: November 2024

The carbonatites in India are closely associated with alkaline rocks, and are restricted to the stable continental area along major deep-seated faults. The detailed structural settings of all the carbonatite-alkaline complexes are yet to be worked out. Alkali metasomatism (fenitisation) that commonly accompanies carbonatite eruption also remains to be studied for most of the carbonatites so far discovered. Very little geochemical work has been done to prove or disprove the concept of associational major and minor element characteristics of the alkaline rocks and carbonatites. Whereas highly diagnostic isotope ratios have been reported for the igneous carbonate rocks from various parts of the world, only very few determinations have been done on the Indian carbonatites. Since experimental data have proved the magmatic origin of carbonatites and it is presumed that carbonatites are secondary magmas out of either kimberlitic or alkali-basaltic magmas, the ultrabasic rocks associated with the alkaline rocks and carbonatites of India need to be studied from the point of view of establishing the parent magma. Carbonatites have proved to be hosts for numerous economic mineral deposits. It is, therefore, necessary to undertake extensive geochemical surveys of the known outcrops as well as of the soils overlying and surrounding the outcrops.
Geology and Mineralisation in the Southern Parts of Bundelkhand in Lalitpur District, Uttar Pradesh
Authors: Prakash Ravi , Swarup Prem , Srivastava R. N.
Published: November 2024

The rocks of the Archaean basement complex and the overlying sedimentary sequences in the southern parts of the Bundelkhand in Lalitpur-Jhansi region, Uttar Pradesh are divided into tectonic blocks, within which broad but distinct stratigraphic units are recognised and classified. Recent mapping suggests that the entire area was subject to two major phases of sedimentary-volcanic process before regional granitisation during the Archaean. Granitisation, in preferred tectonic block, led to the development of an intra-cratonic belt controlled between lineaments, within which the younger Bijawar-Vindhyan basins developed.

The results of exploration done so far suggest that base-metals, gold, uranium and possible nickel mineralisation occurs within the different stratigraphic-tectonic environments recognised in this area.
Genesis of the Barakar Sediments of North Karanpura Coalfield, India as Revealed from Petrography and Provenance Study
Authors: Mukhopadhyay P. K.
Published: November 2024

The petrographic and provenance study of the sediments of Barakar Formation in North Karanpura Coalfield reveals the presence of cyclic sedimentation from coarse to fine clastics, coal and clay arkose. The evidences indicate that the sediments were deposited in a broad river channel with intermittent flooding.
Metamorphism and Petrogenesis of the Dalli-Rajhara and Ari Dongri Iron Formations, Madhya Pradesh
Authors: Mukharya I. L.
Published: November 2024

The minerals present in the iron formations are divided into oxides, silicates and sulphides. Hematite occurs in all the three stratigraphic members and magnetite is present mainly in Ari Dongri. Sulphides are present only in the Ari Dongri Iron Formation. The amphibole group is predominant amongst the silicates. Stilpnomelane and minnesotaite are also present.

The rock types are phyllites, schists, talcose and ferruginous shales, iron-formation, amphibolites, traps, granites and gneisses. The iron-formation consists of banded hematite-quartzites, shales and banded magnetite-quartzites, The unaltered banded hematite-quartzites are of two types-granular and non-granular or slaty. The latter is more common than the former. The rocks which are associated with the ore deposits are ferruginous shales and banded hematite-quartzites. The amphibolites are considered to be metabasites. The basic intrusives are predominant at Ari Dongri.

The silicates are secondary derived by diagenetic or low grade metamorphic effects. Metamorphism increased the grain size in case of hematite and magnetite. There is no coincidence of the metamorphic zones with the boundaries of the stratigraphic units. The cross-cutting relations of the acidic and mafic rocks are thought to be probably related to the last stages of metamorphism.
Carbonatite Alkali Complex of Samalpatti Dharmapuri District, Tamil Nadu
Authors: Subramaniam V. , Viladkar S. G. , Upendran R.
Published: November 2024

Dunites, pyroxenites, alkali syenites and carbonatites form the complex. The complex intrudes in a discordant fashion, hornblende gneisses which form the country rock.

The carbonatites are distributed mainly in pyroxenite as fracture fillings and to a lesser extent as dykes in syenites. The carbonatite bodies form a distinct but discontinuous ring. The calcite-dolomite carbonatite and para-ankerite carbonatite are the main types. Varieties having mica, monazite, riebeckite and ilmenite are identified. Quartz-baryte-galena veins, pegmatites of syenitic composition and albitites are associated with the carbonatites. Evidences for fenitisation are not much. Feldspathoids, normally associated with carbonatite activity are absent. Xenoliths of gneisses, pyroxenite and syenite in carbonatites, compositional banding and primary foliation, are some of the features of the carbonatites. On the basis of mineral assemblage, the temperature of formation of this complex is assigned 325°C. Analyses indicate relatively high values for barium, cerium, yttrium, zirconium, vanadium and boron.
Charnockite-Gneiss-Complex Relationship in Southern Karnataka
Authors: Ramiengar A. S. , Ramakrishnan M. , Viswanatha M. N.
Published: November 2024

The charnockites of southern Karnataka occur at the fringes of the greenstonemigmatite terrain. The contacts of the individual pods and balls of charnockite with the associated migmatites are invariably diffuse. Replication of all types of migmatitic structures by the conformable charnockite masses and pods, and discordant 'tree-structure' of charnockites transecting the early rnigrnatitic fabric of the gneisses strongly suggest that the gneiss complex has been transformed in situ into charnockite without much attendant ductile deformation. The mineralogy of the transformation phenomenon reflects the transitional nature of the amphibolite-granulite facies boundary, rather than a craton-wide regional retrogression. These transformed charnockite buds probably represent nuclei of dehydration.

The major 2900-3000 m.y. thermal event in the gneiss complex, involving the high-grade supracrustal rocks, is correlatable with the progressive metamorphism of amphibolite to granulite facies in the region. This event probably culminated in the production of charnockite around 2600-2700 m.y.

The progressive metamorphism in Karnataka from green schist to granulite facies is shown to be the cumulative effect of polymetamorphism and regional synclinorial structure plunging northward. Post-Dharwar uptilting of the Peninsula has served to accentuate this vertical zonation. As a result deeper crustal levels are exposed southward, involving older supracrustal rocks. The high-grade terrain in Karnataka is, therefore, older than the greenstone terrain. The greenstones and granulites were not juxtaposed against each other because of their differing levels. Parts of the high-grade terrain later evolved into a mobile belt of charnockite-khondalite association. This mobile belt has been interpreted variously as geosynclinal orogenic belt, collision feature similar to the Circum-Pacific belts of the Himalayas, or as a transform zone. The continent-continent collision model is preferred.
The Geology and Origin of Magnomagnetite Deposits from Trap Area of Siberian Platform
Authors: Pavlov N. V.
Published: November 2024

Distribution and localization of iron-ore deposits of Siberian platform appears to be controlled by the disjunctive dislocations in the upper structural level of the platform, conjugated with deep faults in the basement. The peculiar features of the ores and near ore metasomatite composition indicate their connection with trap-magma. Ore-bearing solutions, responsible for the formation of magnomagnetite deposits, are likely to originate as a result of interaction of trap-magma rich in iron with halogene facies of the lower horizons of platform with the formation of iron chlorides. Geological data indicates, that magnomagnetite deposits formed at depths from 300 to 2000m from surface. The variable composition of magnomagnetites and different parageneses of accompanying mineral phases is probably related to different depths of formation.
Sm-Nd and Rb-Sr Ages for Archaean Rocks in Western Karnataka, South India
Authors: Drury S. A. , Holt R. W. , Van Clasteren P. C. , Beckinsale R. D.
Published: November 2024

A Sm-Nd whole-rock isochron age of 3020 ± 230 Ma for basal rnetavolcanics of the Kudremukh-West Coast greenstone belt and a Rb-Sr whole rock age of 3280 ± 230 Ma for the underlying granitoid gneisses are presented. These ages indicate that the filling of an ensialic basin with volcanic and sedimentary rocks began at around 3000Ma and confirm earlier studies which concluded that the dominant gneisses of Karnataka represent a major period of primary crust formation in the South Indian Craton at about 3300 Ma. Both the early granitoid gneisses and the younger metavolcanics were derived from unfractionated mantle sources which had not previously been depleted or enriched in LIL elements.
Crustal Structure Across the Narmada-Son Lineament, Central India from Deep Seismic Soundings
Authors: Kaila K. L. , Reddy P. R. , Dixit M. M. , Koteswara Rao P.
Published: November 2024

The crustal structure along Ujjain-Mahan profile reveals a layered structure in the vertical direction and block structure in the lateral direction. This profile from north to south is divided into four crustal blocks: I (Ujjain-Sanwer), II (Indore-Dorwa), III (Dorwa-Tapti) and IV (Tapti-Mahan) which were relatively displaced up or down during different times along deep faults bounding them and extending up to the Moho discontinuity. The depth to Moho varies between 37 to 42 km along the entire length of the profile with a velocity jump of 7.3 to 7.8 km/sec across the boundary. It is concluded that during Precambrian, blocks I and II north of Dorwa were downthrown with respect to block III leading to the development of the Vindhyan basin in that region. Blocks III and IV being uplifted at that time, formed the land part and hence no Vindhyan sedimentation took place there. Subsequently during Gondwana times, reverse tectonic movement resulted in downfaulting of block III where Gondwana sedimentation took place. During this period, blocks I and II formed the land part and hence no Gondwanas were deposited there. A shallow refraction boundary at a depth of 8 to 12 km has also been observed along this profile with a velocity jump from 6.0 to 6.9 km/sec, which may represent the Conrad discontinuity in this region.

In the Ujjain-Dorwa section comprising blocks I and II, under a thin cover of about 100 m of Deccan Traps, there lie Cretaceous Lameta beds (200m thick) and Vindhyan quartzites (lOa m thick) and Bijawars (200 to 300 m thick). Thus the total sedimentary thickness above the crystalline basement is hardly 600metres in this region. On the other hand, the Dora-Mahan section, consisting of blocks III and IV, has a maximum thickness of about 1.7 km Gondwana sediments underlying 400 metres of Deccan Traps. This hidden Gondwana basin is believed to be a northwestward continuation under the Deccan Trap of the exposed Gondwana-Godavari graben.
A Study on the Time Relations Between Movements, Metamorphism and Granite Emplacement in the Middle Proterozoic Delhi Supergroup Rocks of Rajasthan
Authors: Roy A. B. , Das A. R.
Published: November 2024

The Delhi Supergroup rocks, an important tectonic-stratigraphic unit of the Aravalli Mountains, are affected by multiple folding and polyphase metamorphism. Three generations of deformational structures have been recognized in these rocks (DFI, DF2 and DF3). DFI structures which include a set of isoclinal folds with penetrative axial planar schistosity, were deformed successively by DF2 and DF3 folding movements. Microtcxtural studies of rocks yielded evidence for two metamorphic events-a progressive metamorphism (M1) rising upto epidote amphibolite facies, followed by a retrogressive phase (M3) under greenschist facies condition. Field and microscopic studies indicate that both DF1 and DF2 structures were formed during Ml phase, and DF3 structures were formed during the retrogressive phase (M2). The metamorphic climax of M1 phase was during the early phase of DF2, and the granites emplaced coevally with this event indicated ca. 1450 Ma Rb/Sr isochron age. No definite relationship could be established for the 850-700 Ma secondary (mineral) ages with DF3 deformation and M2 metamorphism.
Mass Spectrometric Diagnostics of Plasmas - Negative Ions in an Oxygen Glow Discharge
Authors: Krishna Kumar S. V.
Published: November 2024

An introduction to mass spectrometric diagnostics of plasmas with an emphasis on the study of glow discharge plasmas is presented. Relative intensities of the negative ions present in a pure oxygen plasma has been studied as-a function of gas pressure, discharge current and reduced electric field (E/N) using a quadrupole mass spectrometer. The variation in the intensity of different negative ions is attributed to the gas phase reactions involving electrons, neutral species, excited molecules, positive ions and negative ions.
Textural Studies on the Ores of Amjhore Pyrite Deposit, Rohtas District, Bihar, India
Authors: Pandalai H. S. , Chandra D.
Published: November 2024

The pyrite ore body at Amjhore occurs as a horizontal to sub-horizontal 'bed' composed, in part, of a hard massive variety and, in part, of a more friable disseminated variety of ore. Microscopic studies reveal that the disseminated ore is made up chiefly of large spherules of pyrite (100,.μm to 1200,.μm in dia.) in a matrix of shale containing also dispersed subhedral toeuhedral pyrite (4,.μm to 30 μm in size). Occasionally, large isolated hexahedral grains of pyrite are also present in the disseminated ores. The microscopic studies indicate development of pyrite spherules from initially close-spaced growth nuclei (perhaps of the precursor-mineral pyrite). The spherules and hexahedra of pyrite fuse together to give fise to the massive variety of ore which show such textures on etching. The textural studies alone cannot, however. be used to infer the exact genesis of the deposit.
Archaean Stromatolites from Dodguni Belt of Karnataka Craton, India
Authors: Baral Mohan C.
Published: November 2024

Long, straight columnar stromatolite structures showing concentric arrangement of laminae in cross-sections are reported from the dolomitic marble of Chitradurga Group from Dodguni, An Archaean age, not less than 2600Ma and not more than 3000 Ma (the minimum and maximum possible age-limits of the Chitradurga Group) has been assigned to the stromatolite-bearing horizon. Presence of organic microstructures and organic carbon in the sediments provided the earlier indirect and controversial evidence of primitive life in this area. The find of these stromatolites undoubtedly confirms the existence of Archaean life in the Dodguni belt.
Geochemical Studies of Soil, Bedrock and Stream Sediment Around Base Metal Mineralization in Tiranga Hill, Bhilwara District, Rajasthan, India
Authors: Bheemalingeswara K. , Deb M. , Banerjee D. M.
Published: November 2024

The Tiranga Hill is located in the southernmost part of the 25 km long Pur-Banera mineralized belt in the Bhilwara District of Rajasthan. Exploration by Government agencies has revealed low grade Pb-Zn-Cu sulfide mineralization along this Early to Middle Proterozoic metasediments and meta-volcanics, regionally metamorphosed to amphibolite facies. At Tiranga, the mineralization occurs within a metamorphosed banded iron-formation spatially associated with spectacularly-folded banded magnetite quartzite (BMQ) bands.

The soils, neglecting the effects of ancient workings, are highly anomalous in Pb and Zn and also to certain extent in Cu. The major anomalies coincide spatially with the cores of synformal folds in BMQ bands, suggesting structural control of the richer parts of the mineralization. The Tiranga soils display strong interelemental correlations between Cu, Pb, Zn, Ag, Fe and Mn, The base metals display similar dispersal behaviour in soils and stream sediments. Their relative mobility in the weathering zones of Tiranga Hill is : Zn >Cu >Pb. Somewhat surprising, however, is the lower concentration of Fe and Mn as well as Ni and Cr in the soils compared to the bedrock.
Angular Unconformity, Structural Unity Argument and Sargur-Dharwar Relations in Bababudan Basin
Authors: Ramakrishnan M. , Viswanatha M. N.
Published: November 2024

Recent mapping by the authors in southern Bababudan has confirmed tbe angular unconformity between the Dharwar cover and Sargur-Peninsular Gneiss basement. The original structural trend of Sargur Group is preserved in an unmodified form in the low strain zone near Kalasapura. In the structural domain of eastern Bababudan with its N-S trends, the underlying Sargur enclaves retain their old N-S orientation but with minor rotation and enhancement during Dharwar overprinting. The apparent structural unity between the basement and cover, therefore, is due to the repetition of a stress regime similar to that of Sargur during the later Dharwar orogeny, which is a common feature of most Archaean cratons. Even in such domains of superposed deformation, the Sargur Group is lithologically distinct from the Dharwar cover rocks and occurs as a train of migmatised enclaves in Peninsular Gneiss, whereas the Dharwar cover forms a large athwart-lying fold belt with mature basal conglomerate preserved in the unaffected parts. These are prima facie evidences for separation of the Sargur and Dharwar into two distinct orogenies. Structural unity per se, divorced from regional stratigraphic considerations, is apt to be grossly misleading in interpreting the geological history of multiple deformed terrains.
Application of Gas and Water Chemistry to Various Geothermal Systems in India
Authors: Saxena V. K.
Published: November 2024

Gas and water studies on sixteen geothermal manifestations (34-97°C) from four geothermal provinces of India have been used to evaluate the reservoir temperatures. The pH of deep thermal waters and partial pressures of CO2 gas have been estimated at probable rock-water equilibrium temperatures. Sub-surface temperatures for geothermal manifestations as estimated by gas and silica geothermometers range from 50 to 163°C and show a good correlation.
Unusual Composition from the Cumulate Section of Andaman Ophiolite
Authors: Ray K. K. , Sengupta S. , Van Den Hul H. J.
Published: November 2024

Mafic and acid cumulates from Andaman ophiolite contain hornblende and magnetite as primary cumulus phases. Four samples with higher SiO2range, contain in addition apatite and quartz crystallised from intercumulus liquid. These have lower Ni, Cr and higher total REE abundances than ophiolitic gabbros and plot away from the field of ophiolitic cumulates in the AFM diagram. Strong negative Eu-anomaly is in striking contrast to ophiolitic cumulates.

No volcanic rocks are associated with these cumulates. Volcanic rocks occurring in a different thrust slice are similar to 'transitional' ridge basalts. It is suggested that the cumulates have crystallised from melts more evolved than ridge tholeiites and possibly from melts similar to basaltic andesites of Andaman ophiolite. in a shallow magma chamber.
Genus Worthoceras Adkins from Cretaceous Deposits of Tiruchchirapalli District, Tamil Nadu, India
Authors: Vartak A. V. , Ghare M. A.
Published: November 2024

Paper reports the presence of the genus Worthoceras Adkins from the Utatur Group, Cretaceous deposits of Tiruchchirapalli, Tamil Nadu. The genus is represented by three species, viz., Worthoceras vermiculian, W. gibbosum and Worthoceras sp. aff. W. rochatianum. History and phylogenetic position of the genus is discussed in detail. Authors following Henderson (1973), place the Wortoceros species under the family Scaphitidae and consider the genus Otoscaphites Wright as an evolutionary form in the lineage Eoscaphites-Scophites.
Estimates of Palaeodiameters of the Earth through Geological Time
Authors: Ahmad F.
Published: November 2024

Palaeozoic palaeopoles deduced from palaeomagnetic data and from the distribution of glacial deposits are in accord for some of the south polar positionst confirming that it was in the north-west of Morocco in the Cambrian. In Upper Permian the pole had moved to the south-east of South Africa, almost in the middle of Antarctica in the Pangaea assembly used here. The Cambrian North Pole, was similarly in Antarctica and migrated to the Verkhoyansk region in the Permian.

Palaeontological data show unequivocally that India was not involved in long distance drift and collision with the northern continents, as advocated by plate-tectonics protagonists. Instead, it existed in its present relationships with the other continents since at least the Cambrian, and may be earlier. The 'Indus Suture' concept is not valid and Chinese geologists, on the basis of their work in the area, are emphatic on the point. Pangaea, thus, existed as a large, composite super-continent comprising the entire existing continental crust, and both the poles were located over this landmass.

The pole positions indicated above go to suggest that in the Upper Permian, the Earth, with the North pole near Verkhoyansk and the South Pole south east of South Africa was 55-60% of its present diameter. The Cambrian diameter, measured similarly, was smaller. For other Palaeozoic periods, the diameter can be similarlyestimated reasonably accurately.

This suggests that the Earth is expanding, and it is probable that the rate of expansion has progressively accelerated through time.
Archaean-Proterozoic Boundary in India
Authors: Radhakrishna B. P. , Ramakrishnan M.
Published: November 2024

Greenstone belts in India are predominantly Archaean with minor development in Proterozoic. The important greenstone belts of India, like the Dharwar of South India, Iron-Ore Group of Eastern India and Bailadilla Group of Central India, are of Late Archaean age and show characteristics transitional to Proterozoic. The end of the Archaean is marked by a burst of granitic activity.

Two independent continental blocks-a southern Peninsular Block and a northern Foreland Block are recognised. The Early Proterozoic successions in India are formed in rifted basins fringing these two Archaean cratonic blocks. These Early Proterozoic cover-rocks and the Archaean basement have invariably been deformed together in Middle Proterozoic, pointing to substantial crustal shortening. The narrow continuous fold belts like those of Aravalli, Delhi, and Satpura, mark the sites of the coming together of the different continental blocks to form a single Indian continent as we see today. A comparable situation is that of the Great Lakes Tectonic Zone of Central North America. Geological, geochronological, geochemical, palaeo-magnetic and palaeobiological considerations which help in demarcating the boundary are outlined.

Ideally, in order to more precisely demarcate the stratigraphic boundary, specific rock units have to be identified in the rock succession in each of the regions. Present data is insufficient and the available maps are on too large a scale to permit identification of boundary stratotypes.
Aeromagnetic Evidence of Crustal Structure in the Granulite Terrane of Tamil Nadu-Kerala
Authors: Reddi A. G. B. , Mathew M. P. , Singh Baldau , Naidu P. S.
Published: November 2024

As conventional mapping of near-surface geology has been completed already on a certain scale for most part of the country, the primary objective of the on-going National Aeromagnetic Survey seems to lie in uncovering the structural configurations at depth by producing relief maps at one or more levels within the crustal column, although such maps cannot but be tentative and open to revision in the light of new data.

This exercise has been attempted for the peninsular segment south of 12°N latitude resulting in the production of a map of a relatively shallow magnetic basement. A filtered (low-pass) anomaly map is also presented that apparently reflects a deeper simatic layer and, therefore, the Moho, by implication. The area seems to be composed of a mosaic of independent crustal blocks involved in relative vertical movements. A graben is indicated sub-parallel to the west coast extending into the Gulf of Mannar and possibly beyond into Sri Lanka. The Palghat-TiruchirapalJi region is also downfaulted suggesting a junction of profound structural dislocation between the granulite terrane and the Karnataka craton. An overall increase in crustal thickness towards north and east is also inferred. The gravity rise towards the Tamil Nadu coast (in striking contrast with the uneventful fatI in magnetic values) may have to be explained in terms of lateral changes in crustal and subcrustal parameters rather than in terms of a simile rise of the Moho.

These results should hopefully encourage the generation of subsurface maps of structure even for the rest of the country based on aeromagnetic and other ground geophysical data, thus, ushering in a new chapter of Indian geology in three dimensions.
2.9 b.y. Rb-Sr Age of the Granulite Facies Rocks of Satnur-Halagur and Sivasamudram Areas, Karnataka, South India
Authors: Mahabaleswar B. , Peucat J. J.
Published: November 2024

Preliminary Rh-Sr isotopic studies of the granulites occurring SW of Kabbaldurga were undertaken to verify the possibility of an earlier granulite facies event. The Rb-Sr data obtained gives an imperfect isochron age of 2950 ± 234 m.y. with an initial ratio of 0.7032 ± 22 (MSWD = 52). The age obtained may correspond to subconcomitant protolith-metamorphism age or metamorphism alone. The high error may be due to non-cogenetic nature of the rocks analysed or a small disturbance of the Rb-Sr system during the 2500 m.y. high-grade event. The present study indicates probability of the occurrence of an early granulite facies event prior to 2500 m.y.
Radiolarian Occurrences in Surface Sediments of the Indian Ocean in Relation to Bottom Water Circulation
Authors: Sharma V. , Mahapatra A. K.
Published: November 2024

Occurrences of radiolaria in the surface sediments collected at 22 stations in the Indian Ocean are noted. While some samples contain abundant radiolaria, others show extremely poor concentration, or, are practically devoid of them. A distinct relationship is found between radiolarian abundance and deep water current systems. It is suggested that the occurrence of radiolaria is largely controlled by currents which are responsible for dissolving radiolarian skeletons. The assemblage is dominated by warm-water species and also contains a few cold-water forms. The cold-water species are believed to be transported by the Antarctic Bottom Waters (AABW) to the present area.
Geology and Structure of the High-Grade Rocks from Punalur-Achankovil Sector, South India
Authors: Radhakrishna T. , Mathai John , Yoshida M.
Published: November 2024

The Punalur-Achankovil sector is a southwestern segment of the high-grade granulite terrain of South India. It is characterised by charnockite and garnet-biotite. Quartz-feldspar (GBQF) gneiss with minor occurrences of sillimanite and graphitebearing gneiss and basic granulite. Structurally. The terrain has undergone three phases of intense deformation and metamorphism and a late less intense deformation. The first deformation (D1) has disrupted original depositional layering with development of quartzo-feldspathic bands; the accompanying metamorphism (M1) is represented by granulite facies sillimanite-bearing gneiss and basic granulite. The second deformation (D2) resulted in isoclinal folding and the corresponding metamorphism (M2) produced large neosome now represented by the GBQF gneiss. Lithologies representing the D3-M3 event are the charnockite and minor granite bodies developed under high-grade metamorphic conditions; open to tight" asymmetric folds are characteristic of this deformation. The final deformation (D4) is less penetrative and is characterised by open folds. Structural data from the area do not indicate any major shear zone features nor does the region constitute an intercratonic suture belt as suggested earlier. The topographic expression along Achankovil-Punalur represents only a neotectonic lineament.
Palaeoenvironmental Reconstruction of the Early Proterozoic Kolhan Siliciclastic Rocks, Keonjhar District, Orissa, India
Authors: Ghosh Sumit K. , Chatterjee B. K.
Published: November 2024

The early Proterozoic Kolhan sihciclastrc rocks of the Kolhan Group (c. 2100 Ma) exhibit extensive-development of thickly bedded sandstone, impersistent conglomerate and siltstone. Six major lithofacies were recognised, viz, granular lag (GLA), granular sandstone (GSD), sheet sandstone (SSD). parallel laminated sandstone (PLSD), rippled sandstone (RSD) and thinly laminated siltstone-sandstone (TLSD). The vertical and lateral arrangement of lithofacies with their general finmg upward sequence is interpreted to reflect superimposition of retrograding shoreline on the earlier, prograding humid alluvial fan-sandflat complex and can be comparable with the present day storm-induced sedimentation on the NW Atlantic shelf.
The Podili Syenites - A Suite of Alkaline and Subalkaline Rocks from Andhra Pradesh
Authors: Madhavan V. , Sugrive Reddy A. G.
Published: November 2024

The alkali syenites of Podili represent a mildly undersaturated nepheline nonnative microsyenites (NNMS) and quartz nonnative microsyenites (QNMS). All the microsyenites have developed nonnative acmite and are totally free from normative hypersthene. In contrast, the quartz syenites always carry normative hypersthene and are invariably devoid of normative acmite.

In the variation diagrams. the PodiIi syenites form distinct petrochemical trends indicating their consanguineous relationship. A dichotomous differentiation trend is discernible.
Some Observations on the Phosphatic Rocks of the Lower Gondwana Sequences of the Ib River Coal Field, Sundergarh District, Orissa, India
Authors: Raha Pulak Kumar
Published: November 2024

The phosphate occurs as discontinuous patches forming massive compact claystone-like rocks. Submicroscopic grains of quartz, feldspar and flakes of mica, and grains of cryptocrystalline rock fragments and chert occur in a phosphatised ground mass. Coarsely crystalline calcite and siderite of secondary origin are commonly associated. The cores of nodular masses show altered. olivine, pyroxene, prismatic calcic plagioclase, rock and chert fragments, and vein-quartz in a coarsely crystalline carbonate cement, while the outer shells of the nodular bodies are of amorphous phosphatic material. Trace-element analyses show high values of Ba, Y, and La in phosphatic rocks compared to non-phosphatic ones. An igneous source for the clasts in the cores of nodular bodies and secondary phosphatisation through late hydrothermal solutions are suggested.
Submarine Debris-Flow Deposits from the Ordovician Mane Ting Formation in Tethyan Black Mountain Basin, Central Bhutan
Authors: Bandyopadhyay B. K. , Gupta Anupendu
Published: November 2024

The rocks in the basin range in age from Early Ordovician to Devonian. Proximal sedimentation began with the deposition of an orthoquartzite-conglomerate lithofacies of the Nake Chu Formation. Rapid sedimentation coupled with quicker subsidence initiated a period of instability that led to the deposition of the distal facies sediments of the Mane Ting Formation characterised essentially by interbanded quartz wacke and shale with an input of andesite. A number of conformable interbedded para-conglomerate beds, identified as submarine debris flow deposits, occur within this Mane Ting Formation.

Lithic fragments ranging in size from 1 mm to 2 m and upwards constitute one modal class and are of diverse types, including quartz wacke, shale, quartzite and chert and limonitised clasts. Monocrystalline quartz, muscovite, siderite and feldspar in combination with the matrix define the second mode with size ranging from 1/4 to l/200 mm. The bimodality is interpreted to be due to mixing of the coarse sand and gravel component with the matrix.

Intact load structures and convolute folds in rip-up clasts and rafts, very poor sorting with high mud matrix, angularity of the constituent fragments. chaotic and often vertical orientation of the platy clasts and the presence of mud balls, armoured sand grains and shale-coated clasts strongly suggest transportation within a high density, cohesive debris-flow.
Pre-Monsoon Living Planktonic Foraminifera from the Southeastern Arabian Sea
Authors: Guptha M. V. S. , Divakar Naidu P. , Muralinath A. S.
Published: November 2024

Examination of 39 vertical zooplankton hauls from the southeastern Arabian Sea for living planktonic foraminifera showed the presence of 28 species indicating highest diversity during summer of the year 1985. The maximum recorded abundance off Cape Comorin was 3100/1000 m3. while the highest abundance of 1320 specimensl 1000m3was encountered off the coast of Kerala.

Based on the planktonic foraminifera, two assemblages of summer tropical Arabian Sea and summer Arabian Sea upwelling were encountered off Kerala coast and south of Cape Comorin respectively. Foraminiferal diversity observed was quite high in this region. The standing crop of planktonic foraminifera encountered was highest off Cape Comorin coast.