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

N. W. Gokhale ¹, V. C. Chavadi ¹

Affiliations
1 Department of Geology, Karnatak University, Dharwar, IN

Abstract

The paper deals with the plagiodases occurring in the gabbro pluton of Vajrat. 133 twinned plagioclase grains from 26 rock samples of these gabbros are studied on the 4-axes universal stage. The anorthite content and the twin laws of these plagiodases have been determined on the lines of Reinhard. Areal variation map is prepared for the anorthite content of the plagioclases, on the lines of Dawson and Whitten. Petrographic studies of the gabbros indicate that the gabbros of the more central parts of the pluton are distinctly fine grained ru. compared to the grain size of those forming the peripheral portion. The areal variation pattern of the anorthite content together with the petrographic characters of the gabbros suggest more than one period of igneous activity in the formation of the Vajrat gabbro pluton.

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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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P. T. Hanamgond ¹, V. C. Chavadi ²

Affiliations
1 Department of Geology, G.S. Science College, Belgaum-59000, IN
2 Department of Studies in Geology, Karnatak University, Dharwad-580 003, IN

Abstract

Granulometric studies of 317 sediment samples collected at different micro-environments were used to understand the depositional environment and their spatial (cross-shore and longshore) and temporal (seasonal) grain size variations. The study involves EOF analysis to understand the size distributions at each of the micro-environments through different seasons. With the help of the available textural tools sediment movement and high energy areas have been distinguished.

Keywords

Sedimentology, Beach, West Coast, Karnataka.

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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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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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