- C. Mallikarjuna
- N. R. R. Ballal
- T. R. Narayanan Kutty
- G. V. Anantha Iyer
- M. N. Viswanatha
- N. Chayapathi
- Brian Chadwick
- V. Srinivasa Murthy
- A. S. Ramiengar
- G. R. Devadu
- B. L. Chadwick
- J. Swami Nath
- Samit Bhattacharyya
- B. Chadwick
- A. K. Ghosh Roy
- N. H. G. Garrioch
- B. P. Radhakrishna
- M. Santosh
- N. S. Reddy
- B. Mahabaleswar
- A. P. Nutman
- B. K. Rastogi
- P. L. Narula
- V. P. Kamble
- G. D. Gupta
- P. Sangurmath
- H. P. Sharda
- D. Sundaravanan
- S. P. Venkata Dasu
- A. Kroener
- S. Moorbath
- P. N. Taylor
- S. Viswanathan
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Ramakrishnan, M.
- The Indian Precambrian
Authors
1 Geological Society of India, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 53, No 3 (1999), Pagination: 379-380Abstract
No Abstract.- Precambrian Crustal Processes in East Coast Granulite-Greenstone Regions of India and Antarctica Within East Gondawana
Authors
1 Geological Society of India, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 53, No 4 (1999), Pagination: 505-505Abstract
No Abstract.- Carbonatite Dyke in Mysore State
Authors
1 Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 14, No 2 (1973), Pagination: 200-201Abstract
No Abstract.- Quartz-Fibrolite Nodules from Bastar and Balaghat Districts, Madhya Pradesh
Authors
1 Jayanagar, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 15, No 1 (1974), Pagination: 100-102Abstract
No Abstract.- Mineralogy of an Unusual Alteration Product of Kyanite from Karnataka, India
Authors
1 Jayanagar, Bangalore, IN
2 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 16, No 3 (1975), Pagination: 326-336Abstract
An alteration product of kyanite from Kudinirkatte near Holalkere, Karnataka State, is found to be a hydrous alumino-silicate with a chemical composition corresponding to that of muscovite. Thermal, X-ray diffraction, and infrared spectral data show distinct variation from the known polymorphs of muscovite. On hydrothermal reactions with potassium-rich solution, the alteration product converts to 1M muscovite, and in sodium-rich solution, it converts to a mixture of muscovite and paragonite. When seeded, it converts to 2M muscovite at a higher temperature and pressure. The alteration product of kyanite has a 1M muscovite structure with randomly distributed montmorillonite domains.
- Konkanhundi Pluton: A New Layered Basic Intrusion from Karnataka
Authors
1 Jayanagar, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 2 (1976), Pagination: 207-213Abstract
Konkanhundi pluton is the first recorded occurrence of a layered basic intrusion in Karnataka. It is an oval shaped mass having an area of 50km2 and is composed mainly of layered gabbro with cumulates of gabbro, norite and anorthosite, arranged concentrically. Non-layered norites are also conspicuous. Rhythmic layering is ubiquitous and cumulus textures are not uncommon. The pluton is emplaced into the gneissic complex of the Archaean high grade terrain. Subsequent to emplacement, it has been deformed and metamorphosed. It is considered to be a magmatic intrusion emplaced under plutonic conditions.- Possible Spinifex Texture in a Serpentinite from Karnataka
Authors
1 17, Raja Mahal Vilas Extension, Bangalore 560006, IN
2 63, Geetha Colony, Jayanagar, IV Block, Bangalore 560011, IN
3 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 18, No 4 (1977), Pagination: 194-197Abstract
No Abstract.- Geology and Geochemistry of Anorthosites of Karnataka Craton and their Tectonic Significance
Authors
1 17, Raja Mahal Vilas Extension, Bangalore-560006, IN
2 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560012, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 19, No 3 (1978), Pagination: 115-134Abstract
Anorthosites of Karnataka occur in two distinct tectonic milieu, within a major arcuate zone, namely, (i) as minor differentiates of gabbro in the ultramafic-mafic complexes emplaced in Archaean high-grade supracrustal belts and the 'Dharwar type' greenstone belt of Shimoga; and (ii) as layered concordant sheets, and as cumulates in a layered basic pluton occurring within the gneissic complex of Archaean high grade terrain. Their absence in 'Keewatin type' greenstone belts and the other 'Dharwar type' belts of Bababudan and Chittadurga is probably due to their location away from the arcuate zone in Karnataka Craton. This arcuate zone reflects a progressive vertical zonation of the crust to deeper levels from northwest to southeast.
The anorthositic rocks of mafic-ultramafic complexes are nonlayered and extensively deformed, whereas those of the high grade terrain show layering and cumulus textures. In the transitional zone, the anorthositic rocks of mafic-ultramafic complexes show cumulus textures, thereby indicating a genetic connection between the anorthosites of two tectonic milieu.
Whole-rock chemistry of the anorthosites of Karnataka indicates differentiation trend of iron-poor environment comparable to other Archaean anorthosites. They are enriched in CaO and A12O3 Niggli mg against Cr or Ni shows positive correlation, corresponding to an igneous parentage for the original rock. Similarly, the plot of Niggli c against mg, c against (al-alk) and 100 mg-c-(al-alk) diagrams exhibit a well defined igneous trend. A common differentiation trend is shown by anorthosites of Karnataka, even though they occur in two distinct tectonic milieu. The singularised trends support the view that the ultramafic-mafic complexes are possibly derived by the dismembering of the basal parts of the layered complexes. The Archaean anorthosites of Karnataka, although comparable broadly to lunar anorthosites, are not related to the early history of the Earth-Moon system.
- Structural Studies in the Archaean Sargur and Dharwar Supracrustal Rocks of the Karnataka Craton
Authors
1 Department of Geology, The University, Exeter EX44QE, GB
2 Geological Survey of India, Karnataka Circle (South), Bangalore 560041, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 19, No 12 (1978), Pagination: 531-549Abstract
Structural studies in the linear supracrustal belts and adjacent Peninsular Gneiss in the areas of Sargur, Holenarsipur and Chitradurga have revealed Land S tectonites and related structures, which are attributed to phases of deformation SgDl, SgD2 and SgD3 in the older Sargur Group and DhDI, DhD2 and DhD3 in the younger Dharwar Supergroup. These phases gave rise to comparable patterns of strain in each group, the deformation taking place with similar timing relative to metamorphism. Metamorphic grade is higher (middle to upper amphibolite facies) in the Sargur Group and lower (upper greenschist to lower amphibolite facies) in the Dharwar Supergroup: the higher grade assemblages in the Sargur Group show some degree of retrogression. The structures and fabrics in both groups may either be of approximately the same age (SgD1=DhDl, SgD2=DhD2, SgD3=DhD3) or more probably, the SgDI, SgD2 and SgD3 structures and fabrics in the Sargur Group may be older and were rotated into parallelism with younger structures formed in the Dharwar Supergroup during phases of deformation DhD1 and DhD2 that gave rise to the present form of the linear belts of supracrustal rocks extending from Sargur to Chitradurga. Some aspects of the Archaean tectonometamorphic evolution of the Karnataka Craton are discussed in the light of these alternatives.- Banded Chromite-Fuchsite Quartzite in the Older Supracrustal Sequence of Karnataka
Authors
1 Geological Survey of India, Jayanagar, Bangalore-560011, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 19, No 12 (1978), Pagination: 577-582Abstract
A small enclave of ancient supracrustal rocks (Sargur Group) in Kamataka contains an interesting occurrence of fuchsite quartzite with layers of chromite and other heavy minerals like magnetite, tourmaline, rutile and zircon. The opaque and non-opaque heavy mineral suite is suggestive of a source region rich in sialic components with subordinate ultramafic rocks. This is consistent with the spatial association of these supracrustal rocks with a vast gneissic complex containing numerous enclaves of chromite-rich ultramafic rocks in the vicinity.- Charnockite-Gneiss-Complex Relationship in Southern Karnataka
Authors
1 Geological Survey of India, Karnataka (South) Circle, V Block, Jayanagar, Bangalore-560041, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 19, No 9 (1978), Pagination: 411-419Abstract
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.
- Foundation of the Sargur Group
Authors
1 Department of Geology, The University, Exeter EX4 4QE, GB
2 Geological Survey of India, Karnataka Circle (South), Bangalore 560041, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 20, No 5 (1979), Pagination: 248-255Abstract
No Abstract.- Angular Unconformity Between Sargur and Dharwar Supracrustals in Sigegudda, Karnataka Craton, South India
Authors
1 Geological Survey of India, Hyderabad 500 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 23, No 2 (1982), Pagination: 85-89Abstract
The major angular unconformity between the Peninsular Gneiss and Dharwar Supergroup in Sigegudda belt, Karnataka, is now 'discovered' to separate the Sargur from Dharwar Supracrustals. It is the most critical area known so far in the craton to exemplify the Sargur-Dharwar relationship. In conformity with modern stratigraphic practice, the unconformity marked by supermature conglomerates incontrovertibly separates two major rock sequences in early Precambrian geological record of Karnataka Craton.- Structural and Metamorphic Relatioms Between Sargur and Dharwar Supracrustal Rocks and Peninsular Gneiss in Central Karnataka
Authors
1 Department of Geology, University, Exeter EX4 4QE, GB
2 Geological Survey of India, Hyderabad 500001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 22, No 12 (1981), Pagination: 557-569Abstract
The Dharwar Supergroup and its basement of Peninsular Gneiss and Sargur supracrustal rocks in the areas of Ghatti Hosahalli and southeast Bababudan display certain textural, structural and unconformable relations which have important implications for the Archaean chronology of the Karnataka craton. In the first. instance these relations show that certain tonalitic-granitic parental rocks of the Peninsular Gneiss basement to the Dharwar supracrustal rocks were formed as a series beginning with polyphase gneisses and ending with discordant plutons such as the Chikmagalur granite s.l. The Sargur rocks were deformed and metamorphosed to medium-high grade during intrusion of the polyphase gneisses. After cooling, uplift and erosion of the Peninsular Gneiss and the tracts and enclaves of Sargur rocks, the Dharwar supracrustal association was deposited unconformably on the medium-high grade basement. The pre-Dharwar metamorphic minerals in the Sargur rocks were partly retrogressed and then overprinted by a second major metamorphism, mainly low grade, whose climax was attained after the main deformation of the belts and basins of the Dharwar supracrustal rocks. This major low grade metamorphism in central Karnataka is correlated with the later Archaean high grade terrane (ca. 2600 Ma) in southern Karnataka and elsewhere in Peninsular India.- Geological Evolution of the Earth during the Precambrian
Authors
1 Geological Survey of India, Gujarat Circle, Ahmedabad 380014, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 25, No 3 (1984), Pagination: 197-198Abstract
No Abstract.- Contact Metamorphic Granophyres of Partial Melting Origin Adjacent to Dolerite Dykes in Karnataka
Authors
1 Geological Survey of India, Gujarat Circle, Ashram Road, Ahmedabad 380014, IN
2 Geological Survey of India, OME and MG Wing, 4, Chowringhee Lane, Calcutta 700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 2 (1985), Pagination: 95-102Abstract
Granophyric rocks produced at the contact of post-Dharwar dolerite dykes in the host gneisses and granites of Peninsular Gneissic Complex stand out conspicuously at the weathered dyke margins in the vicinity of Hole Narsipur, Karnataka. The degree of development of granophyric texture is variable, and with its progressive increase, there is a shift in the host rock composition from granodiorite to alkali granite. Since there is no possibility of addition of potash from the dolerite to the granodiorite (the reverse is commonly the case) to cause this potash enrichment in host rocks, the origin of granophyres in the contact zones is attributed to partial melting rather than metasomatism or assimilation. This view is consistent with experimental evidence that partial melting of sodie gneisses (tonalites, trondjhemites and even granodiorites) results in the production of more potassic rocks like adamellites and alkali granites. The production of granophyres in the present case is, therefore, taken as a textural evidence for the partial melting of quartzofeldspathic gneisses. Similar phenomena are observed at the contact of Skaergaard intrusion of Greenland and Newer Dolerite of Singhbhum in eastern India.- 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
1 Department of Geology, University, Exeter EX4 4QE, GB
2 Geological Survey of India, Hyderabad 500001, IN
3 Geological Survey of India, Jayanagar IV Block, Bangalore 560011, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 8 (1985), Pagination: 526-546Abstract
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
1 Geological Survey of India, Doris (E.R.), Calcutta 700071, IN
2 Geological Survey of India, Hyderabad 500001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 8 (1985), Pagination: 567-579Abstract
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.- Bababudan - A Late Archaean Intracratonic Volcanosedimentary Basin, Karnataka, Southern India
Authors
1 Department of Geology, University, Exeter EX4 4QE, GB
2 Geological Survey of India, Mukhramjahi Road, Hyderabad 500 001, IN
3 Geological Survey of India, Jayanagar IV Block, Bangalore 560 011, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 11 (1985), Pagination: 769-801Abstract
The stratigraphy of the volcanosedimentary rocks of the late Archaean Dharwar Supergroup that make up the Bababudan basin is described in terms of six lithostratigraphic divisions, in ascending order, the Kalasapura, the Allampur, the Santaveri, the Mulaingiri, the Jagar and the Mundre Formations, the Jagar and the Mundre Formations being lateral equivalents. The three lower formations, each varying in thickness from a few metres to about 2000m, are dominated by metabasaItic rocks with local cross-bedded quartzites, including the basal quartz-pebble Kartikere Conglomerate which unconformably overlies the basement Peninsular Gneiss (c. 3100 Ma) in the south; the western, northern and eastern boundaries of the basin arc steep faults. The Mulaingiri Formation (200-1500m) is dominated by banded ferruginous cherts interbedded with phyllites, the Jagar Formation (? up to 2000m) comprises poorly exposed metabasaltic rocks and phyllites on the west of the basin, and the Mundre Formation, restricted to the northeast, contains the KaIdurga Conglomerate with a lower division dominated by clasts of Dharwar cover and an upper division dominated by clasts of Peninsular Gneiss basement: the conglomerate passes laterally into phyllites and crossbedded quartzites. The Mundre Formation is intruded by small bodies of pre- or syn-tectonic granite s.l.
The lithostratigraphic formations thicken from west to east indicating greater subsidence of the basin in the east, with the thickest accumulations marked by the Kaldurga Conglomerate (7 up to 5000 m) in the northeast. Sedimentary facies suggest that relatively shallow, intertidal or nearshore, marine environments persisted throughout most of the depositional and volcanic phases of basin development with banded ferruginous cherts and interbedded phyllites accumulating in areas (also relatively shallow ?) starved of terriginous detritus. The Kaldurga Conglomerate built out as a composite, shallow marine and alluvial cone into a rapidly subsiding part of the basin, detritus being provided by erosion of uplifted cover and basement to the north and northeast.
- Bababudan - A Late Archaean Intracratonic Volcanosedimentary Basin, Karnataka, Southern India. Part II: Structure
Authors
1 Department of Geology, University, Exeter EX4 4QE, GB
2 Geological Survey of India, Mukhramjahi Road, Hyderabad 500 001, IN
3 Geological Survey of India, Jayanagar, IV Block. Bangalore 560 011, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 26, No 11 (1985), Pagination: 802-821Abstract
The boundary between the Dharwar volcanosedimentary rocks and their basement (Peninsular Gneiss, c. 3100 Ma, with tracts and enclaves of the Sargur supracrustal association) on the south of the Bababudan basin is an unconformity, faulted and steepened in the southeast by inclined folds verging to the south. These folds pass east into a complex area of neulral folds and faults. Boundaries between the Dharwar cover and its basement on the west, north and east of the basin are steep or vertical faults. Basement gneisses within 2-3 km of the eastern and western boundary faults are intensely schistose or mylonitic with L and LS fabrics identical to those in the cover rocks. The S fabrics in the cover and basement in the east of Bababudan are steep or vertical and associated L fabrics have variable, gentle to moderate plunges to the north or south. Displacement on the eastern and western boundary faults appears to have been dominated by uplift of the basement and shortening at a high angle to the S. fabrics. Movements on the northern boundary fault gave rise to mylonites and tectonic melanges. in the basement and cover and took place before movements on the eastern and western boundary faults and folding in the northeast (Kaldurga syncline and the Nandi arch) and northwest (Lakkavalli syncline) of the basin. Further faulting (Tarikere Fault) related to basement uplift in the northeast occurred during or after folding in the cover.
The structure within the basin is dominated by steep faults and upright open folds with strongly curved hinge lines within steep axial surfaces. The Bababudan syncline is an open east-west fold which curves gently westwards into a tight cusp trending north parallel to the western boundary fault. East of the syncline the structure is dominated by the upright open arch and complex saddle zone of the Santaveri anticline. LS fabrics associated with the Bababudan syncline, the Santaveri anticline and other major folds within the basin have widely variable trends but their continuity from one structure to another suggests the folds, fabrics and faults formed contemporaneously with synchronous refolding that gave rise to the curved axial surfaces such as that of the Bababudan syncline. Synchronous refolding and rapid variations in style of small-scale folds are especially common in the multilayer complexes of banded ferruginous cherts. Whilst fabrics are mostly of LS type, L tectonites indicative of intense constrictional strains are prominent in the east. Mineral lineations and elongated clasts and amygdales forming the L fabric arc commonly parallel to fold axes.
The geometrical relations between upright folds, steep faults and LS fabrics and the effects of synchronous refolding suggest the Dharwar volcanosedimentary rocks deformed in response to constriction by segments of basement rising on all sides of the Bababudan basin, the rise beginning in the norlh. Uplift of basement segments with widespread, pervasive retrogression related flushing of fluids, including CO2, through myriad cracks and narrow shear zones, especially north of the Bababudan basin, may have taken place as part of a regional thermal event manifested at the present level of outcrop by the Arsikere and Banavara granites to the east. The case for tectonic thickening by thrusts and nappe emplacement reported in Archaean terranes elsewhere has not been proved in the Bababudan basin.
- Mineral Composition, Textures and Deformation in Late Archaean Banded Iron-Formation Rich in Magnesioriebeckite and Aegirine, Bababudan, Karnataka, Southern India
Authors
1 Department of Geology, University of Exeter, Exeter EX4 4QE, GB
2 Department of Geology, University of Exeter, Exeter EX4 4QE, IN
3 Geological Survey of India, Hyderabad 500001, IN
4 Geological Survey of India, Bangalore 560011, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 28, No 2&3 (1986), Pagination: 189-200Abstract
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.
- Angular Unconformity, Structural Unity Argument and Sargur-Dharwar Relations in Bababudan Basin
Authors
1 Geological Survey of India, Precambrian Geology Division, Chandra Vihar, M. J. Road, Hyderabad 500001, IN
2 No. 17, Rajamahal Vilas Extension, Bangalore 560080, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 29, No 5 (1987), Pagination: 471-482Abstract
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.- Precambrian Geology of India
Authors
1 Centre for Earth Science Studies, Trivandrum 695 031, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 32, No 5 (1988), Pagination: 439-440Abstract
No Abstract.- Archaean-Proterozoic Boundary in India
Authors
1 Geological Society of India, Bangalore 560019, IN
2 Centre for Earth Science Studies, Trivandrum 695 010, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 32, No 4 (1988), Pagination: 263-278Abstract
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.
- Volcanic Hazards: Assessment and Monitoring
Authors
1 Geological Survey of India, AMSE Wing, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 34, No 5 (1989), Pagination: 547-548Abstract
No Abstract.- Mafic and Ultramafic Xenoliths from Volcanic Rocks of the Western United States
Authors
1 Geological Survey of India, A.M.S.E. Wing, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 34, No 5 (1989), Pagination: 548-548Abstract
No Abstract.- Annual Report of the National Geophysical Research Institute (1988-89)
Authors
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 36, No 1 (1990), Pagination: 95-95Abstract
No Abstract.- Phanerozoic Ophiolites of India
Authors
1 Geological Survey of India, A.M.S.E. Wing, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 34, No 4 (1989), Pagination: 439-440Abstract
No Abstract.- 'Pseudo-Charnockites' from the Greenstone Terrain of Northeast Dharwar Craton
Authors
1 Centre for Earth Science Studies, Trivandrum 695 031, IN
2 Geological Survey of India, Hyderabad 500 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 35, No 6 (1990), Pagination: 593-603Abstract
Patches and oriented zones of 'pseudo-charnockites', similar in appearance to incipient charnockites from the granulite transition zones, are reported for the first time from the pink granites of Gadwal and Kurnool areas in the low-grade metamorphic terrain of northeast Dharwar craton. With a mineral assemblage of quartz, feldspars, micas and amphiboles showing varying degrees of alteration to chlorite and sericite, these zones preserve the signature of hydration following peak metamorphism. Though aqueous brine inclusions (average 6 wt % NaCl equivalent) constitute the dominant fluid phase in the granite and the retrograde zones, the occurrence of coexisting monophase inclusions with a near-pure carbonic fluid (density 0.70-0.80g/cm3) in the retrograde zones invoke special attention. Though carbonic inclusions generally typify dehydration reactions, it is suggested that retrograde reactions of the type which produced the pseudo-charnockite horizons could also result in the entrapment of nearpure CO2 of moderate to low densities. The carbonic inclusions have apparently resulted from the immiscible separation of a mixed carbonic-aqueous fluid which exsolved into brine and CO2 upon decompression following the rapid uplift of the Eastern Block along the Chitradurga boundary fault, concomitant with the copious intrusion of younger granitoids.Keywords
Andhra Pradesh, Dharwar Craton, Fluid Inclusion, Greenstone Terrain, Pseudo-Charnockite.- Geology of Tin Deposits in Asia and the Pacific
Authors
1 Geological Survey of India, AMSE Wing, Bangolore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 34, No 6 (1989), Pagination: 673-673Abstract
No Abstract.- An Introduction to the Geology of Sri Lanka (Ceylon)
Authors
1 Geological Survey of India, A.M.S.E. Wing, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 36, No 5 (1990), Pagination: 547-547Abstract
No Abstract.- Geology of the Ammassalik Region, South-East Greenland
Authors
1 Geological Survey of India, A.M.S.E. Wing, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 36, No 2 (1990), Pagination: 209-209Abstract
No Abstract.- Basement Correlation across the North Atlantic
Authors
1 Geological Survey ofIndia, A.M.S.E. Wing, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 35, No 2 (1990), Pagination: 221-221Abstract
No Abstract.- Field Geology of High-Grade Gneiss Terrains
Authors
1 Geoological Survey of India, R and D Division, AMSE Wing, Bangalore-1, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 37, No 5 (1991), Pagination: 504-505Abstract
No Abstract.- The Applachian-Ouachita Orogen in the United States
Authors
1 Geological Survey of India, R and D Division, AMSE Wing, Bangalore-1, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 37, No 5 (1991), Pagination: 507-507Abstract
No Abstract.- Research Methodology: A Hand Book
Authors
1 Geological Survey of India, AMSE Wing, Bangalore - 560 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 38, No 3 (1991), Pagination: 336-336Abstract
No Abstract.- International Field Workshop and Seminar on Composition and Evolution of High-Grade Gneiss Terrains
Authors
1 Department of Geology, Bangalore University, Bangalore 560001, IN
2 Geological Survey of India (AMSE), Bangalore 560001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 38, No 6 (1991), Pagination: 639-643Abstract
No Abstract.- Shrimp U-Pb Ages of Detrital Zircon in Sargur Supracrustal Rocks in Western Karnataka, Southern India
Authors
1 Research School of Earth Sciences, Australian National University, GPO Box 4, Canberra ACT 2601, AU
2 Earth Resources Centre, University, Exeter EX4 4QE, GB
3 Geological Survey of India, 2 Church Street, Bangalore 560 001, IN
4 17 Rajamahal Vilas Extension, Bangalore 560080, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 39, No 5 (1992), Pagination: 367-374Abstract
New limits have been set on the age of the provenance and the depositional period of the oldest known Archaean supracrustal rocks (Sargur Group) in southern India. Detrital zircon grains from a pelitic schist and a quartzite within major tracts of supracrustal rocks older than their host regional grey orthogneisses (peninsular Gneiss, c. 3000-2900 Ma) have yielded U-Pb ages in the range 3580-2960 Ma. The data indicate that granitoid rocks in the age range 3580-3130 Ma were a significant component of the provenance of the sedimentary protoliths. Ages younger than 3130 Ma are attributed to effects of high-grade metamorphism during emplacement of the igneous precursors to the host orthogneisses. Exhumation of the granitoid provenance, deposition of the sedimentary protoliths, intrusion of major gabbroic and peridotitic complexes and possible basaltic volcanism represented by amphibolites in the tracts of supracrustal rocks took place in the period 3130-2960 Ma. This age range is at variance with previous suggestions that the Sargur Group represents early Archaean or primitive crust.Keywords
Geochronology, Zircon-Dating. U-Pb Ages, Sargur Supracrustals, Karnataka.- Special Issue on Petrology
Authors
1 Geological Survey of India, Training Institute, Bandlaguda, Hyderabad-500 660, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 1 (1994), Pagination: 98-99Abstract
No Abstract.- Workshop on the Eastern Ghats Mobile Belt: A Summary
Authors
1 Geological Survey of India,Training Institute, Hyderabad - 500068, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 3 (1994), Pagination: 348-349Abstract
No Abstract.- Workshop on Killari Earthquake, of 30 September 1993 (Held on 24 December 1993 at Hyderabad)
Authors
1 Geological Survey of India, Hyderabad, IN
2 National Geophysical Res Inst, Hyderabad, IN
3 Geological Survey of India, Lucknow, IN
4 India Meteorological Dept., New Delhi, IN
5 Dept. of Science and Technology, New Delhi, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 43, No 5 (1994), Pagination: 613-618Abstract
No Abstract.- Transformists' Petrology
Authors
1 Geological Survey of India, Training Institute, Hyderabad-560068, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 5 (1994), Pagination: 590-591Abstract
No Abstract.- Atlas of Granitisation Textures and Processess,1993
Authors
1 Geological Survey of India, 27, Jawaharlal Nehru Road, Calcutta-700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 47, No 2 (1996), Pagination: 266-267Abstract
No Abstract.- Second South Asia Geological Congress: A Report
Authors
1 Geological Survey of India, Calcutta, IN
2 Mineral Exploration Corporation Ltd., Hyderabad, IN
3 Geological Survey of India, Lucknow, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 45, No 5 (1995), Pagination: 620-621Abstract
No Abstract.- Shrimp U-Pb Ages of Detrital Zircons in Sargurs
Authors
1 Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, AU
2 Earth Resources Centre, University Exeter EX4 4QE, GB
3 Geological Survey of India, Bandlaguda, Hyderabad 500 660, IN
4 17, Rajamahal Vilas Extension, Bangalore 560 080, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 41, No 2 (1993), Pagination: 164-172Abstract
No Abstract.- Multidisciplinary Techniques in Mineral Exploration - A Case Study
Authors
1 Geological Survey of India, Training Institute, Bandlaguda, Hyderabad - 500 660, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 41, No 2 (1993), Pagination: 178-179Abstract
No Abstract.- Differentiated Gabbro-Granophyre Composite Sill from Ramagiri Greenstone Belt, Andhra Pradesh
Authors
1 Centre for Earth Science Studies, Trivandrum 695031, IN
2 Precambrian Geology Division, Geological Survey of India, M. J. Road, Hyderabad 500001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 35, No 4 (1990), Pagination: 367-379Abstract
The differentiated gabbro-granophyre composite sill, emplaced in the basic tuffs of Ramagiri greenstone belt, represents the first record of such an intrusion in the Eastern Dharwar craton. The sill consists of four differentiated gabbroic units, namely, the carbonated, mafic, normal and knotted gabbro forming a locally inverted stratigraphy along a steep fold limb in the belt. A faintly layered quartz diorite band, visually resembling anorthosite but compositionally different in having euhedral zoned feldspars and quartz-plagioclase "granophyric ' intergrowths, occurs in association with the differentiated gabbroic units but is separated from it by a later metadoleritic amphibolite dyke. The granophyric quartz diorite and the associated quartz gabbro are not directly related to the other four differentiated gabbros of the composite Ramagiri sill. The quartz diorite is chemically similar but tectonically dissimilar to continental trondhjemites forming tbe ischolar_main of island arcs and is different from oceanic plagiogranites and continental granophyres in terms of their K2O, Si02, Rb and Sr contents, although such rocks are not uncommon in the ocean floor. Such quartz diorites are believed to have been formed by fractional crystallisation of oceanic tholeiite magma which interacted with sea water to produce low potassic trends, as distinct from the more potassic granophyre differentiates of continental layered sills. These non-continental granophyres in basic sills, together with the associated pillow lavas and pelagic sediments indicate a nascent oceanic to transitional environment generated by rifting of the basement gneisses to produce the Ramagiri greenstone belt.Keywords
Greenstone Belt, Ramagiri, Andhra Pradesh, Petrology: Igneous, Geochemistry.- Middle Archaean Age of Sargur Group by Single Grain Zircon Dating and Geochemical Evidence for the Clastic Origin of Metaquartzite from J. C. Pura Greenstone Belt, Karnataka
Authors
1 Geological Survey of India, Training Institute, Hyderabad, IN
2 Geological Survey of India, AMSE Wing, Bangalore, IN
3 Institut fuer Geowissenschaften, Johannes Gutenberg-Universitaet, 55099 Mainz, DE
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 6 (1994), Pagination: 605-616Abstract
The middle Archaean J. C. Pura greenstone belt of Sargur Group underlies the Dharwar angular unconformity along the Kibbanahalli arm of Chitradurga schist belt. It consists essentially of periodotitic komatiite (serpentinite), basaltic komatiite (dark amphibolite), rare BIF and minor metaquartzite. In view of the ongoing debate on the origin of Sargur quartzite as to whether it is a chemogenic, biogenic or detrital-rich chert or quartz arenite, the study of J. C. Pura metaquartzite is important as it will have a direct bearing on the depositional setting of the metaquartzite in particular, and the Sargur association in general. In the absence of primary sedimentary structures, accessory zircons in the metaquartzite provide the main clue to its origin. Euhedral zircons with minor rounding of pyramidal terminations in the metaquartzite suggest little mechanical corrosion and negligible sedimentary transport. These zircons are interpreted as detrital grains and the host rock as siliciclastic in origin. Geochemical parameters like Al2O3 vs TiO2, SiO2 and K2O, trace element spider plots, REE patterns and La/Sc ratio indicate a significant continental contribution, low Fe and Mn content, low TiO2-normalised values and variable Co/Zn and Ni/Zn ratios preclude major sea water hydrothermal activity. The proximal provenance indicated by euhedral zircons did not apparently have a significant felsic volcanic component since such rocks are neither present witnin the schist belt nor found as enclaves in the surrounding gneisses. Furthermore, the Sr, Zn, Y, Yb values of the metaquartzite are lower than that of felsic volcanics and pyroclastics, thereby ruling out their prevalence in the source area. The most likely source would therefore be the widespread early Archaean continental crust of southern India made up of granitoids. The metaquartzite was probably deposited as quartz arenite in shallow marine enviroment close to the continent. The associated pillowed komatiite also lends support to this environmental interpretation.Euhedral zircons from J. C. Pura metaquartzite were dated by single grain evaporation technique which yielded a Pb-Pb age of 3230 ± 5 Ma. This date representing the maximum age of the Sargur metaquartzite is fully in accord with previous Sm-Nd model ages and SHRIMP U-Pb zircon ages (ca 3200 Ma) of Sargur rocks from nearby areas. The Sargur Group is pervasively intruded by gneisses and granites around 3000 Ma. Still older gneisses seen in the neighbourhood such as the Gorur gneiss of 3300 Ma age may constitute a possible basement to the Sargur supracrustals and represent widespread early Archaean granitic crust of the Dharwar craton.
Keywords
Geochronology, Geochemistry, Metamorphic Petrology, J. C. Pura/Sasivala Greenstone Belt, Sargur Group, Dharwar Craton, Kanataka.- M. N. Viswanatha (1936 - 1993)
Authors
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 43, No 2 (1994), Pagination: 216-217Abstract
No Abstract.- The Indian Continental Crust and Upper Mantle (A Volume in Honour of T. M. Mahadevan)
Authors
1 Chennai, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 71, No 4 (2008), Pagination: 583-584Abstract
No Abstract.- Gargoti Mineral Museum
Authors
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 69, No 2 (2007), Pagination: 402-402Abstract
No Abstract.- Uniformitarianism Revisited: Comparison between Ancient and Modern Orogens of India
Authors
1 #201, Skyline Surabhi Apartments, Vidyapeetha Road, BSK III Stage, Bungalore - 560085, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 66, No 1 (2005), Pagination: 126-127Abstract
No Abstract.- Earth System Science and Natural Resources Management: Silver Jubilee Compendium
Authors
1 # 201, Skyline Surabhi Apartments, Vidyapeetha Road, BSK III Stage, Bangalore - 560085, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 66, No 2 (2005), Pagination: 256-257Abstract
No Abstract.- Advances in Precambrian of Central India
Authors
1 Geological Sociely of India Bangalore - 560 019, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 63, No 2 (2004), Pagination: 239-240Abstract
No Abstract.- J. Swami Nath-a Tribute
Authors
1 Geological Society of India, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 62, No 3 (2003), Pagination: 388-388Abstract
No Abstract.- Geology of Transvaal Inliers in the Bushveld Complex
Authors
1 201, Skyline Surabhi Apartments, Vidyapeetha Road, BSK III Stage Bangalore - 560 085, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 59, No 6 (2002), Pagination: 596-596Abstract
No Abstract.- National Symposium on Exploration and Survey for Noble Metals and Precious Stones
Authors
1 Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 58, No 1 (2001), Pagination: 83-84Abstract
No Abstract.- Professor Robert Shackleton (1909-2001)
Authors
1 Geological Society of India, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 58, No 3 (2001), Pagination: 277-277Abstract
No Abstract.- Rb-Sr and Pb-Pb Whole Rock Isochron Ages of Basement Gneisses in Karnataka Craton
Authors
1 Geological Survey of India, Gujarat Circle, Ashram Road, Ahmadabad - 380014, IN
2 Department of Geology and Mineralogy, University of Oxford, Oxford, GB
3 Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560012, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 25, No 1 (1984), Pagination: 20-34Abstract
Rb-Sr and Pb-Pb whole rock isotopic systematics and petrochemical data for two suites of Peninsular Gneiss immediately underlying the first order regional unconformity at the base of the main greenstone successions of Dharwar Supergroup in Bababudan and Chitradurga belts are presented.The Chikmagalur granite (s.l.) and associated migmatite gneisses (CMG suite) underlying the Bababudan greenstones define an eleven point Rb-Sr isochron of 3080 ± 80 m.y. (MSWD4.5) with an initial 87Sr/8686 isotope ratio (I.R.) of 0.7016 ± 0004. Pb isotope data for the same samples yield a 3185 ± 60 m.y. isochron (MSWO 7.0) with single stage 238U/204Pb (μ1) ratio of 7.99. The crust-forming event in this area spans a range of 3000-3200 m.y. within the analytical error of the isochrons. The mantle-type I.R. and μ1 values preclude interaction with or reworking of earlier continental crust in their genesis. Petrological and chemical studies of the CMG suite show that the Chikmagalur 'granite' is a biotite granodiorite and the intruded gneisses are low alumina trondjhemites having a calc-alkaline trend. It is significant that the CMG suite is located within a low strain zone in Central Karnataka.
The gneisses and granitoids close to the western margin of the Chitradurga belt (CDG Suite) give a Rb-Sr age of 2970 ± 100 m.y. (MSWD 11) with I.R. of 0.7035 ± 0.0013. The corresponding Pb-Pb isochron defines a date of 3044 ± 150 m.y. with μ1 = 7.69. The μ1 and I.R. values suggest the possible involvement of previous sialic crust in their generation during the gneiss-forming event around 3000 m.y. ago. The CDG suite is heterogeneous, but all its components are regarded as a part of the Peninsular Gneiss. The composition of the CDG suite has a wide range from tonalite to granite, with a typical calcalkaline granitic trend.
Recent intensive geochronological studies in central Karnataka suggest a widespread crust-forming event around 3000 m.y. together with older gneissic components of Ca 3300 m.y. The present data bridge the time gap between 3000 and 3300 m.y. suggesting that continental crust was being generated in Karnataka craton from 3300 to 3000 m.y. semi-continuously. The unambiguous field relations in central Karnataka suggest that this event occurred prior to the deposition of main greenstone piles of Dharwar Supergroup.
- Precambrian Mafic Magmatism in the Western Dharwar Craton, Southern India
Authors
1 8, Manipallavam, 29, Balakrishna Road, Valmiki Nagar, Thiruvanmiyar, Chennai - 600 041, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 73, No Spl Iss 1 (2009), Pagination: 101-116Abstract
Mafic rocks of Western Dharwar Craton (WDC) belong to two greenstone cycles of Sargur Group (3.13.3 Ga) and Dharwar Supergroup (2.6-2.8 Ga), belonging to different depositional environments. Proterozoic mafic dyke swarms (2.4, 2.0-2.2 and 1.6 Ga) constitute the third important cycle. Mafic rocks of Sargur Group mainly constitute a komatiitic-tholeiite suite, closely associated with layered basic-ultrabasic complexes. They form linear ultramaficmafic belts, and scattered enclaves associated with orthoquartzite-carbonate-pelite-BIF suite. Since the country rocks of Peninsular Gneiss intrude these rocks and dismember them, stratigraphy of Sargur Group is largely conceptual and its tectonic environment speculative. It is believed that the Sargur tholeiites are not fractionated from komatiites, but might have been generated and evolved from a similar mantle source at shallower depths. The layered basic-ultrabasic complexes are believed to be products of fractionation from tholeiitic parent magma. The Dharwar mafic rocks are essentially a bimodal basalt-rhyolite association that is dominated by Fe-rich and normal tholeiites. Calc-alkaline basalts and andesites are nearly absent, but reference to their presence in literature pertains mainly to carbonated, spilitized and altered tholeiitic suites. Geochemical discrimination diagrams of Dharwar lavas favour island arc settings that include fore-, intra- and back-arcs. The Dharwar mafic rocks are possibly derived by partial melting of a lherzolite mantle source and involved in fractionation of olivine and pyroxene followed by plagioclase. Distinctive differences in the petrography and geochemistry of mafic rocks across regional unconformities between Sargur Group and Dharwar Supergroup provide clinching evidences in favour of distinguishing two greenstone cycles in the craton. This has also negated the earlier preliminary attempts to lump together all mafic volcanics into a single contemporaneous suite, leading to erroneous interpretations. After giving allowances for differences in depositional and tectonic settings, the chemical distinction between Sargur and Dharwar mafic suites throws light on secular variations and crustal evolution. Proterozoic mafic dyke swarms of three major periods (2.4, 2.0-2.2 and 1.6 Ga) occur around Tiptur and Hunsur. The dykes also conform to the regional metamorphic gradient, with greenschist facies in the north and granulite facies in the south, resulting from the tilt of the craton towards north, exposing progressively deeper crustal levels towards the south. The low-grade terrain in the north does not have recognizable swarms, but the Tiptur swarm consists essentially of amphibolites and Hunsur swarm mainly of basic granulites, all of them preserving cross-cutting relations with host rocks, chilled margins and relict igneous textures. There are also younger dolerite dykes scattered throughout the craton that are unaffected by this metamorphic zonation. Large-scale geochemical, geochronological and palaeomagnetic data acquisition through state-of-the-art instrumentation is urgently needed in the Dharwar craton to catch up with contemporary advancements in the classical greenstone terrains of the world.Keywords
Mafic Magmatism, Precambrian, Sargur Group, Dharwar Craton.- Geology in South Asia-II
Authors
1 Geological Society of India, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 53, No 2 (1999), Pagination: 268-268Abstract
No Abstract.- Basement-Cover Relationships of Peninsular Gneiss With High Grade Schists and Greenstone Belts of Southern Karnataka
Authors
1 Geological Survey of India, Bangalore, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 1 (1976), Pagination: 97-111Abstract
The low grade Archaean terrain of southern Karnataka is composed of greenstone belts and high grade schists set in a sea of gneiss complex (Peninsular gneiss). Peninsular gneiss contains three major components which are inter-gradational, namely: (a) a trimodal macrolayered unit of amphibolites, ultramafites and granite gneiss (b) normal migmatites with characteristic megascopic structures and (c) nebulitic, schlieric and homophanous granitoids. On the whole it is a polymigmatite encompassing several episodes. The ubiquitous enclaves of mafic-ultramafic rocks within Peninsular gneiss probably represent residues of repeated reworking of the crustal rocks. The composition of the gneiss complex varies in the indestructible range of tonalite through granodiorite to granite. The high grade schists or supracrustals consist of shelf sediments, volcanics and ironstones with profuse emplacements of ultramafites. Their contacts with the gneiss complex are concordant due to intense deformation, high metamorphic grade and extensive migrnatisation. This high grade thermal event (Pantectogenesis) dated at 2900-3000 m.y. has acted as an effective smokescreen blurring earlier episodes. Subsequent to the pantectogenesis, greenstone belts were evolved on a basement of gneiss complex. Two types of greenstone belts of mutually exclusive geographic distribution are seen in the craton: (i) dominantly volcanic belts, lacking shelf facies rocks and ultramafics at the base, called the Keewatin type, which are broadly comparable to the Archaean greenstone belts and (ii) Platformal volcanic and protogeosynclinal belts of Dharwar type, which are similar to the early Proterozoic basins and geosynclines. The contacts of the Dharwar type greenstone belts with the gneiss complex are almost always unconformable, whereas in the case of Keewatin type of belts, the contacts are obscured either by soil cover or by massive invasion of later granites. This major granitic event possibly corresponds to the 2500-2600m.y. isochron in the gneiss complex. This evolutionary picture reconstructed mainly from newer field data is consistent with the available limited information on geochronology, geochemistry and mineralisation trends.- Selected Studies of Archaean Gneisses and Lower Proterozoic Rocks, Southern Canadian Shield
Authors
1 Geological Survey of India, Gujarat Circle, Ahmedabad, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 25, No 10 (1984), Pagination: 687-687Abstract
No Abstract.- The Abundances of Some Trace-Elements in the First-Ever Reported Sample of Spinifex-Textured Komatiite from Ghatti Hosahalli, Karnataka
Authors
1 "Manipallavam", 29, Balakrishna Road, Valmiki Nagar, Thiruvanmiyur, Chennai - 600 041, IN
2 Department of Geology, Bangalore University, Bangalore - 560 056, IN
3 Flat B-203, Block-B, United Avenue Apartments, South End, 7-1-29, Ameerpet, Hyderabad - 500 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 79, No 4 (2012), Pagination: 361-366Abstract
The paper reports wavelength-dispersive x-ray fluorescence spectrometric data on the abundances of Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in the first-ever reported sample of spinifex-textured komatiite from India at Ghatti Hosahalli in Karnataka. With some exceptions, these abundances are similar to those reported for the spinifex-textured komatiite from the Barberton greenstone belt in South Africa. The values for some alteration-resistant element ratios - Ti/Zr, Ti/Y, Ti/Sc, Ti/V, Zr/Y, Zr/Sc, Sc/Y, V/Zr, and V/Sc - for chondrite and for spinifex-textured komatiites from Ghatti Hosahalli (India), Barberton (South Africa), Munro (Canada), and Yilgarn (Australia) reveal that, except for the Ti/Zr ratio for the Ghatti Hosahalli komatiite, the other ratios from the four terrains define a unique trend that is almost superimposed on the trend defined by these ratios for chondrite. This suggests that the processes of formation of komatiitic lavas from the four far-separated terrains were similar, and that, the source regions from which these lavas formed had a chondritic composition.Keywords
Komatiite, Trace-Elements, Ghatti Hosahalli, Karnataka, India, Barberton, Munro, Yilgarn.References
- AHRENS, L.H. (1965) Distribution of the Elements in our Planet. McGraw-Hill Book Company, New York, 110p.
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- Geotourist Map of Sri Lanka
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