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

L. P. Sarma ¹, G. Parthasarathy ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

We report here the first observation of a thermally induced irreversible decomposition in natural actinolite, collected from Santaveri, Karnataka, by using DC electrical resistivily measurements upto 1100K. The electrical resistivity of the actinolite sample is found to be 4 X 10¹¹ Ohm-cm at room temperature and pressure. The temperature dependence of the electrical resistivity of the samples exhibits an Arrhenius behaviour ρ = ρ_n exp(ΔE/kT) in the region 300-700 K with an activation energy of 0.76 eV. At 770 ± 5 K a first-order increase in resistivity from 7.93 X 10³ to 3.55 X 10¹⁴ ohm-cm has been observed, which is due to decomposition of the sample. In the temeprature region 775-1100 K, the value of the activation energy is found to be 0.20 eV. X-ray diffraction studies on the thermally quenched samples indicate that the decomposed phase is a mixuture of cummingtonite, clinopyroxene, plus quartz and water vapour as associated products. These breakdown products are found to be identical to those proposed by Cameron (1975), and contrary to the mineral assemblage of fayalite-hedenbergite-pyroxene-quartz-vapour as proposed by Ernst (1966).

Keywords

Mineralogy, Calcic-Amphiboles, Phase Transitions, High-Temperature Electrical Resistivity Studies, Powder X-Ray Diffraction, Kamataka.

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Suresh Kharkhanis ¹, K. S. Misra , M. R. Hammond , Anant V. Phadke , Fiona Plows , U. S. N. Reddy , I. V. Reddy , Fareeduddin , G. Parthasarathy , C. R. M. Rao , B. N. Gohain , Dinesh Gupta

Affiliations
1 Analytical Research Laboratory, Department of Polymer and Petroleum Engineering, MIT Engineering College, Kothrud, Pune - 411 038, IN

Abstract

No Abstract.

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Suresh N. Karkhanis ¹, G. Parthasarathy ², A. S. Collins ², T. R. K. Chetty ²

Affiliations
1 Analytical Research Laboratory, Department of Polymer and Petroleum Engineering, MIT Engineering College, Kothrud, Pune - 4 11 038, IN
2 NGRI, Hyderabad - 500 007, IN

Abstract

No Abstract.

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G. Parthasarathy ¹, Alan S. Collins ², T. R. K. Chetty ¹

Affiliations
1 National Geophysical Research lnstitute, Hyderabad -500 007, IN
2 Continental Evolution Research Group, Geology & Geophysics, School of Earth and Environmental Sciences, The Universlty of Adelaide, Adelade, SA 5005, AU

Abstract

We report here, for the first time, powder X-ray diffraction, and laser-Raman spectroscopic data on the graphite samples from Inanalo mountain (S24°24 3 1 2" E45°23'18 3 ), 20 km east of the Ampanihy shear zone of the southern Madagascar Our experimental results show that the graphite is highly crystalline, and syngenetic with the degree of graphitisation varying from 148 to 180, ylelding the peak metarnorphic temperatures of 750 to 850°C Laser Raman spectroscopic studies show only ordered peak at around 1580 cm-' In the frequency range from I000 to 2000 cm-' The commonly observed disordered peak In natural graphite is found to be absent in the studied sample, indicating high-temperature metamorphism There is no flurd deposited graphite (epigenetlc graphlte) in the sample The peak metamorphic temperature obtained In the present study is found to be in good agreement withinat obtained from the conventional geothermometry studies on the sample from the Beraketa shear zone or the Betroka tectonic belt.

Keywords

Syngenetic graphite, Laser-Raman studies, XRD, Shear Zone, Inanalo Mountain, Southern Madagascar.

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G. Parthasarathy ¹, S. R. Sharma ¹, T. R. Ravindran ², A. K. Arora ², S. M. Hussain ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN
2 Indira Gandhi Centre for Atomic Research, Kalpakkam - 603 102, IN

Abstract

We report here powder X-ray diffraction, differential thermal analysis and Laser-Raman spectroscopic data on the graphite from Schirmacher Oasis (70°45' S, 11°40' E), East Antarctica. The sample was collected from Precambrian garnet-biotite gneiss. The present X-ray studies show that the structural parameters like inter-planar spacing, d₀₀₂ (3.3500 A), and crystallite size, L_c (552 A) of this sample. These values are found to be very close to that of well-crystallized graphite. All the five observed X-ray diffraction peaks have been indexed to the hexagonal phase of graphite, indicating the metamorphic origin of graphite. The observed full width at half maxima (FWHM) of the (002) peak is 0.148 A and the estimated graphitizing degree (GD=13lA) showed the high-grade metamorphism of the host rock. The estimated peak metamorphic temperature is found to be ∼973 K (700°C). DTA studies on the same graphite sample show a strong exothermic peak at 1023 K, which corresponds, to the combustion of carbonaceous matter under atmospheric condition. The absence of extra weak peak in the range 1090-1110 K, indicates the absence of any noticeable detntal graphite in the sample. The first order Laser - Raman spectra of the sample shows a strong well-ordered Raman peak (O) at 1581cm"¹ and a weak broad peak due to disorder (D) at 1354cm"¹. The intensity ratio disordered-to-ordered Raman peak (D/O) area has been used to estimate the in-plan crystallite size (La) of the graphite. The experimental values of D/O = 0.143 and D/D+O = 0.125 indicate that the sample is well crystallized graphite, thereby indicating the high metamorphic grade of the host rocks. The structural parameters obtained by Raman spectroscopic method and the estimated in-plane crystallite size (La = 298 A) indicate that the metamorphic grade of the host rock of the studied sample falls in the sillimanite zone. The present study suggests that the peak metamorphic temperature of the host rock could be in the temperature range of about 973 K (700°C).

Keywords

East Antarctica, Graphite, X-Ray Diffraction, Schirmacher Oasis, High-Temperature Dta, East Antarctica.

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G. Parthasarathy ¹, S. R. Sharma ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad -500 007, IN

Abstract

We report here new experimental results on the high temperature differential thermal analyses (DTA) on six graphite samples from the Dharwar craton, along with the structural data obtained by powder X-ray diffraction, carbon isotopic and Laser Raman spectroscopic studies.

Degree of metamorphism and crystallite size obtained by X-ray studies indicates systematic variation in graphite with peak metamorphic temperatures. X-ray and Laser Raman spectroscopic studies do not show the presence of rhombohedral graphite phase which is the most characteristic of the fluid-deposited (abiogenic) graphite. The most reliable information on the origin of the graphite is provided by the carbon isotopic ratio. However, the interpretation of the isotopic data is usually not straightforward because other processes may influence the original signature. But isotopic fractionation does not alter once the graphite is well crystallized, because of very sluggish kinetics of carbon diffusion. Present studies show that the main exothermic DTA peak temperature of graphite samples decreases linearly with increase of the interplanar d-spacing d (002) of the hexagonal graphite structure and follows the relation d₀₀₂ (Å) = 3.5197 - 1.67 × 10^-4 T(K). These studies also reveal that DTA/thermogravimetric analysis is an effective tool for distinction of detrital graphite material from the poorly crystallized organic matter. Raman spectroscopic results on the same samples indicate systematic change in the metamorphic grade of the host rocks with the intensity ratio of disordered to ordered Raman peaks. These findings confirm that the carbon in the graphite of the metasedimentary host rocks from Dharwar craton is of metamorphic and biogenic origin, thereby confirming the findings of the isotopic studies on the same samples.

Keywords

Graphitization, DTA, Raman Spectroscopy, Karnataka, Dharwar Craton.

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P. Senthil kumar ¹, G. Parthasarathy ¹, S. Das Sharma ¹, R. Srinivasan ¹, P. Krishnamurthy ²

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, IN
2 Atomic Minerals Directorate for Exploration and Research, AMD Complex, Begumpet, Hyderabad-500 01 6, IN

Abstract

Carbonate veins up to few metres thick have been recognised in the E-W striking Salem-Attur deep fault zone which represents the eastern extention of the Moyar fault in the southern granulite terrane of India. X-ray diffraction, FTIR spectroscopy and chemical analyses show calcite, ankerite, siderite and benstonite as dominant minerals besides minor apatite and green biotite. Whole rock compositions show enrichment of light REE, Ba, Sr and Nb. C and 0 isotopic data determined for calcite (δ¹³C= -4.9 to -5.1%0 V-PDB and δ¹⁸0 = 9 to 9.2%0 V-SMOW) points to a mantle origin. The chemical characteristics therefore suggest that the carbonate veins have carbonatitic affinity. The FTIR spectra provide evidence for presence of H₂0 and CH₄ in addition to CO₂ in the carbonate minerals of these veins.

Keywords

Ferrocarbonatites, Benstonite, FTIR Spectroscopy, X-Ray Diffraction, Geochemistry, Isotopes, Tamil Nadu.

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G. Parthasarathy ¹

Affiliations
1 NGRI, Hyderabad, IN

Abstract

No Abstract.

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G. Parthasarathy ¹

Affiliations
1 NGRI, Hyderabad - 500 606, IN

Abstract

No Abstract.

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S. R. Sharma ¹, G. Parthasarathy ¹, T. R. Ravindran ², A. K. Arora ², B. Kumar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN
2 Materials Science Division, Indira Gandhi Centre for Atomic Research, Kalpakkam- 603 102, IN

Abstract

We present here the results of Laser-Raman Spectroscopic studies on graphite samples from the Archaean metasedimentary rocks of Dharwar craton to correlate the structural parameters of graphite with the metamorphic grade of the host rocks. The present studies show that the first order Raman peak (O) of the graphite samples appears in the wave number range from 1581 to 1585 cm^-1; the second order Raman peak (S) appears in the wave number range from 2699 to 2721 cm^-1; and the disorder Raman (D) peak appears in the wave number range from 1349 to 1356 cm^-1. It is suggested that the intensity ratios of the Rarnan peaks (D/O)_a are the inverse function of in-plane crystallite size of the graphite. The observed values of intensity ratio (D/O)_h, varies from 0.095 to 0.591, (D/D+O)_a varies from 0.18 to 0.46 and (S/O)_h, varies from 0.21 to 0.32. This range of values indicates that the graphite samples are well crystallized. A correlation of (D/O) area ratios along with the in-plane crystallite size La (50 to 193 Å) and the metamorphic grade shows that the metamorphic grade of the host rocks of the studied samples lies in the range between upper chlorite zone and lower sillimanite zone. The estmated peak metamorphic temperatures of the host rocks are in the range of 575 to 625°C and they are in excellent agreement with temperatures obtained by the Powder X- ray diffraction studies and conventional geothermometry studies.

Keywords

Raman Spectroscopy, Graphite, Carbon Isotopes, Metamorphic Temperature, Dharwar Craton, Karnataka.

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S. R. Sharma ¹, G. Parthasarathy ¹, B. Kumar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500007, IN

Abstract

We report here., the results of powder x-ray diffraction studies on six graphite samples from the Archaean metasedimentary rocks of Dharwar craton, with the motivation of correlating the graphitization process of carbonaceous matter during metamorphism with metamorphic grade. Our studies show that interplanar spacing d(002) and crystallinity L_c(002) for all the studied samples are very close to that of well crystallized graphite.

The observed decrease in full width at half maximum (FWHM) of the (002) diffraction peak from 0.20 to 0.102 Å. increase in crystallite size, L_c(002) from 408 to 800 Å and graphitizing degree from 86 to 362 indicate different metamorphic grades. Our results indicate that the rocks from Hampapura are of low metamorphic grade and those from Arjun Bettahalli are highly metamorphosed. The peak metamorphic temperatures of metasedimentary rocks are estimated to be around 600±50°C. The temperature estimates based on graphite crystallinity studies and the temperatures estimated by silicate mineral geothermometry studies of the coexisting mineral assemblages were found to be consistent.

Keywords

Mineralogy, Graphites, X-Ray Diffraction, Metamorphic Grade, Peak Metamorphic Temperatures, Dharwar Craton.

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