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

K. R. Hari ¹

Affiliations
1 Govt. Arts & Science College, Durg (M. P.) 491 001, IN

Abstract

Three lamprophyre dykes with E-W trend which cut across alkali olivine basaltic rocks and their differentiates are noticeable in the vicinity of Chhaktalao area. Clinopyroxene and olivine phenocrysts are set in a matrix of clinopyroxene, plagioclase, biotite, apatite, spinel, magnetite/ titanomagnetite, ilmenite and calcite. On the basis of Na₂O and K₂O percentages, these rocks are classified as alkaline lamprophyre (camptonite) and calc-alkaline lamprophyre (kersantite). Clinopyroxene phenocrysts in both the lamprophyres are of augitic composition; whereas few grains and bleb like structure in the groundmass are of salite composition. Fo% of olivine varies from 83.4 to 88.3. Both the rocks are nepheline normative. The camptonite have lower normative orthoclase, Na₂O+ K₂O, K₂O/Na₂O, Σ REE and Ce/Yb values than that of kersantite. These rocks do not carry any primary magma signature as they have low Mg' [Mg/(Mg + 0.9Fe) atomic], Ni, Cr, and Ni/MgO values. High alkali, REE, Ba, Sr contents in these lamprophyres indicate that source region got metasomatically enriched in these elements.

Keywords

Geochemistry, Lamprophyre, Petrogenesis, Madhya Pradesh.

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K. R. Hari ¹, M. Santosh ², A. C. Chatterjee ³

Affiliations
1 Department of Geology, Govt. Arts & Science College, Durg, M. P., IN
2 Centre for Earth Science Studies, P.B.7250, Akkulam, Trivandrum 695 031, IN
3 School of Studies in Geology, Vikram University, Ujjain, M.P., IN

Abstract

Fluid inclusion studies in olivine phenocrysts from alkali olivine basalt, iddingsite basalt and three-phenocryst basalt of the Pavagad igneous suite, an outlier of the Deccan Trap, indicate the presence of highly evolved primary silicate-melt inclusions with various daughter crystals of olivine, pyroxene, plagioclase and opaques. High temperature experiments using a heating stage indicate homogenization in the range of 1040 to 1240 °C. The gas bubble within these inclusions show melting close to the triple point forpure carbon dioxide and homogenize into liquid phase between 25 and 31 °C, denoting densities of 0,70-0.50 g/cm³. Trapping pressure estimated from CO₂ equation of state barometry is about 3.8 kbar, which translates to a depth of formation of ca. 10 km. This correlates well with an independent depth estimate of 10-14 km derived from combined melt and fluid homogenization data. The melt inclusion chardcteristics in the Pavagad suite suggesllhatlhe olivines equilibrated from a slow cooling system at high pressure conditions, the parental melt having a probable alkali olivine basalt composition.

Keywords

Silicate-Melt Inclusions, Olivine, Daughter Crystals, Homogenization, Temperature, Pressure, Pavagad Igneous Suite, Deccan Trap, Fluid Inclusions.

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K. R. Hari ¹, C. G. Nambiar ², K. Furuyama ³, Suneet Kumar Rai ¹

Affiliations
1 Govt. Arts and Science College, Durg - 491001, Chhattisgarh, IN
2 Dept. of Marine Geology and Geophysics, Cochin University of Science and Technology, Kochi - 682016, Kerala, IN
3 Dept. of Geosciences, Osaka City University, Osaka 558-8585, JP

Abstract

Chhaktalao area situated 25 km NE of Ambadongar, is characterised by six flows of Deccan Trap. Of these two are tholeiitic basalts, one picrite basalt and three basaltic andesites. These flows are intruded by east-west trending dolerite, olivine dolerite, lamprophyres and carbonate-rich dyke-like bodies. In this paper the genetic relation between the flows and the dykes (dolerite and olivine dolerite) are discussed. Trace element geochemistry suggests that crustal contamination is not significant and did not play any vital role in the evolution of the lava flows and dykes. The dolerite and olivine dolerite dykes and mafic members of the flows show similar trace element characteristics indicating a broad chemical affinity between these two magmatic phases.

Keywords

Deccan Trap, Flows and Dykes, Geochemistry, Petrogenesis, Madhya Pradesh.

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K. R. Hari ¹, M. Satish Kumar ², M. Santosh ³, Suneet Kumar Rai ¹

Affiliations
1 Government Arts and Science College, Durg, Madhya Pradesh 491 001, IN
2 Department of Geoscience, Osaka City University-559, JP
3 Centre for Earth Science Studies, P.B.No. 7250, Akkulam, Trivandrum - 695 018, IN

Abstract

Carbonate-rich rocks occur as E-W trending dyke-like bodies in the Deccan 'basalts at Chhaktalao area in the lower Narmada valley and show a structurally controlled mode of emplacement. Modal composition shows calcite as the dominent mineral (∼90%). Ankerite, apatite, altered olivine, augite and opaques account for the remaining percentage. Geochemically, these rocks show high CaO (>50%) with low SiO₂, TiO₂, FeO* and K₂O. Trace element concentrations are low compared to average carbonatites. Stable isotope studies show that δ¹³C(-1.74‰ to -2.8‰) and δ¹⁸O(+12.75‰ to +13.35‰) values do not compare with those of "primary igneous carbonatites" eventhough they fall within the wide range of "igneous carbonatites". These rocks can be considered only as carbonate-rich rocks and not as true carbonatites.

Keywords

Petrology, Carbonate-Rich Rocks, Stable Isotope, Nannada Valley, Madhya Pradesh.

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K. R. Hari ¹, N. V. Chalapathi Rao ², Vikas Swarnkar ¹

Affiliations
1 Government V.Y.T.PG. Autonomous College, Durg, Chhattisgarh, IN
2 Centre of Advance Study in Geology, Banaras Hindu University, Varanasi – 221 005, IN

Abstract

We report the occurrence of orthopyroxene gabbro from the Phenai Mata Igneous Complex (containing thoeliitic and alkaline rocks) that occur within Deccan Traps. The P-T calculations based on two pyroxene thermometry vary from 8.5±1.0 kbar and 963±39 °C. These gabbroic rocks exhibit high Mg# (0.67 to 0.71). But their primary magma signature can be negated due to their high SiO₂ ( > 50 wt %), low Ni (32-35 ppm) and Cr (105-182 ppm) contents. Further, simple fractional crystallization was not responsible for the modification of the magma. Modeling carried out using trace element concentrations revealed that concurrent assimilation and fractional crystallization (AFC) was responsible for the genesis of these rocks. Small pods of magma could have accumulated in the crustal portions and concurrent assimilation and fractional crystallization have taken place in the generation of gabbro and orthopyroxene gabbro in the present study area.

Keywords

Orthopyroxene, Deccan Traps, Concurrent Assimilation and Fractional Crystallization, Gabbro, Phenai Mata.

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