Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

V. C. Chavadi ¹, V. S. Hegde ¹

Affiliations
1 Department of Studies in Geology, Karnatak University, Dharwad 580003, IN

Abstract

The greywackes of Ranibennur are granodioritic in composition, and have been deposited in eugeosynclinal basin under reducing conditions. Matrix of the greywackes indicates operation of more than one process for its origin.

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S. Viswanathan ¹, V. S. Hegde ²

Affiliations
1 B-160, Ananta, IIT Campus, Powai, Mumbai - 400 076, IN
2 SDMCET, Dharwad - 580 002, IN

Abstract

No Abstract.

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V. S. Hegde ¹, V. C. Chavadi ²

Affiliations
1 S D M College of Engineering and Technology, Dharwad-580002, IN
2 "Chinnaganga", Chennabasaveshwaranagara, University Cross, Srinagar, Dharwad-580003, IN

Abstract

High Mg-tholentic dykes occur around Arabail in the Dharwar-Shimoga schist belt in Western Dharwar Craton. They are olivine-rich to quartz poor-normative type. The dykes are enriched in light rare earth elements (Σ 47-63, La_N/Yb_N,=78 to 1327). Their composition is analogous to Continental Flood Basalts. The geochemical characteristics suggest that source magmas are partial melts of periodotitic mantle followed by fractional crystallization. The composition of the dykes appears to have been controlled by olivine and pyroxene fractionation followed by plagioclase in the late phase of fractionation. The dyke magma may have been formed by decompression melting consequence of lithospheric extension, crustal thinning or plume impingement at the base of the lithosphere. Deep extensional fracture systems might have served as conduits for emplacement of the dykes.

Keywords

Dolerite Dykes, Tholentic Magma, Continental Flood Basalt, Petrogenesis , Western Dharwar Craton.

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V. S. Hegde ¹, D. Kanchanagouri Gosavi ¹

Affiliations
1 Civil Engineering Department, S.D.M. College of Engineering and Technology, Dharwar -580 002, IN

Abstract

Metaluminous (Alumina Saturation Index A/CNK < 1.04), acid volcanic rocks ranging in composition from rhyolite to dacite occur in St Mary's island. The rocks are rich in SiO, (68.58-71.27%), high field strength elemenls, moderately rich in AI₂O₃, (1 1.78-15.02%), and low in CaO, MgO. V, Cr, and Ni. They are characterized by fractionated light rare earth elements (La/Sm=6.8) and a flat heavy rare earth elements pattern with a large negative Eu anomaly (0.48). Variation in bulk- rock major and trace element composition together with mineral data on clinopyroxene composition, suggest a basaltic precursor and a cause related to rifting. The enrichments of incompatible elements point to an EM-I type mantle source. From the over all geochemical characteristics, it is inferred that the Marion plume caused the lower part of the basaltic crust to soften, stretch and rift in an extensional setting. The rise in the geotherm caused by the rising asthenosphere and the pressure change resulting from rifting lowered the solidus temperature and resulted in partial melting of the basaltic crust. Subsequent fractionation produced dacitic to rhyolitic magma, which was emplaced in a rift setting.

Keywords

Plume related, Acid volcanic activity, Columnar structure, Rhyolite-Dacite, Geochemistry, Petrogenesis, St. Mary's Island, South Kanara District, Karnataka.

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V. S. Hegde ¹, B. K. Koti ², P. T. Hanamgond ³, G. Shalini ¹, K. H. Girish ¹

Affiliations
1 S.D.M. College of Engineering and Technology, Dharwad - 580 002, IN
2 K.L.E. College of Engineering and Technology, Belgaum-6, IN
3 G.S.S. College of Tilakwadi, Belgaum - 6, IN

Abstract

Beach sediments of Pavinkurve and Kasarkod, located adjacent to the Sharavati River mouth at Honnavar, Central West Coast of India are medium to fine grained (1.21 - 2.30Φ) and moderate to well sorted (0.17-0.55). The convergence of long-shore circulation and interaction of river and wave processes are the main influence for the distribution of sediments along these beaches. The sediment transport land-ward during fair weather season (pre-monsoon) is mainly due to westerly wave approach. The re-suspension of sediments owing to agitation of sea during westerly wave approach, their land-ward movement during high tide, and the obstruction caused by the submerged bar formation during falling tide leading to their deposition are the main causes for siltation in the river mouth.

Keywords

Depositional environment, Longshore current, Estuarine beach, Texture, West Coast of India.

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M. S. Bhat ¹, V. C. Chavadi ², V. S. Hegde ¹

Affiliations
1 SDM College of Engineering and Technology, Dharwad - 580 002, IN
2 Department of Geology, Karnatak University, Dharwad - 580 003, IN

Abstract

Morphological and textural studies of Kudle beach have been made at monthly intervals over a period of one year to understand its dynamics. The studies have revealed that the beach shows cyclic changes in its morphology, i.e. erosion during the SW monsoon and accretion during the fair-weather season, followed by a secondary cycle of erosion during NE monsoon (December/January and January/February). The beach experienced a net gain of 321.45 m³/m of sediments during the study period (February 1993 to February 1994). The sediments are predominantly fine grained (90.71%), very well sorted (55.78%), positively skewed (37.29%) and leptokurtic (44.12%). C-M pattern revealed graded suspension sediments reflecting moderate turbulent conditions during deposition. Morphological and textural studies suggest that the sediment movement is predominantly due north along this beach.

Keywords

Morphology, Monsoon, Textural Characteristics, Kudle Beach, Karnataka.

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