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

B. Basavalingu ¹, K. Byrappa ¹, P. Madhusudan ¹

Affiliations
1 Department of studies in Geology, University of Mysore, Manasagangotri, Mysore - 570 006, IN

Abstract

The hydrothermal synthesis of diamond was carried out in the silicon carbide - organic compound system. The organic compounds were expected to dissociate in a closed system to generate C-O-H supercritical fluids, which are known for their high dissolving power and influence on the type of elemental carbon formation, especially in stabilizing the sp³-hybridized carbon. The SEM studies reveal that the bulk portions of the carbon formed are spherical/ovoid shaped particles and in a few cases nanosized crystallites. The micro Raman spectral studies of carbon crystallites reveal that they are having typical spectra of sp³-hybridization, thus clearly demonstrating the formation of nano-sized diamond crystallites under sub-natural conditions. In all the above investigations metal catalysts or the seeded diamond were not used, unlike in earlier attempts on the hydrothermal synthesis of diamond.

Keywords

Diamond, Hydrothermal Synthesis, Nanosized Crystals.

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K. Francis Anto ¹, A. S. Janardhan ¹, B. Basavalingu ¹

Affiliations
1 Department of Geology, University of Mysore, Manasa Gangotri, Mysore-570006, IN

Abstract

Kambam valley forms an integral part of the Southern Granulite Terrain. The valley represents a deep crustal break hosting high temperature alkaline intrusives and also a carbonatite body. Common rock types encounterd are charnockite and granulite grade calc-silicate and metapelite. Calc-silicate lithologies are interbanded with mafic granulites on cm scale. Wolfastonite-scapolite-grandite garnet-clinopyroxene indicate high temperature (900°C). Corroborative high temperatures are recorded from associated rnetapelites. Textural features such as the formation of coronal garnet and garnet-quartz double rinds at the expense of calcite, scapolite, wollastonite, clinopyroxene suggest a late isobaric cooling at shallower depths. The cooling event was associated with domainal variation in fluid species. Fluid inclusion studies confirm a late carbonic fluid flux consistent with the carbonation reactions that followed.

The associated metapelitic lithologies in the area preserve textural evidence for a rapid high temperature decompression event. The Kambam valley granulites, thus witnessed high temperature metamorphism, rapid decompression and late isobaric cooling. The above metamorphic history is consistent with those reported from other parts of the Southern Granulite Terrain (SGT). Thermal perturbation associated with extensional thinning and alkaline magmatism explain the high temperature metamorphism, decompression and subsequent cooling.

Keywords

Petrology, Calc-Silicate, High Temperature Granulites, Metamorphic History, Southern Granulite Terrain, Tamil Nadu.

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J. A. K. Tareen ¹, A. R. Fazeli ¹, B. Basavalingu ¹, G. T. Bhandage ²

Affiliations
1 Department of Studies in Geology, Mysore University, Manasagangotri, Mysore 570006, IN
2 Department of Chemistry, Regional College of Education (NCERT), Mysore 570006, IN

Abstract

The P-T stability field of rhombohedral double carbonates, CaMg (CO₃)₂ (dolomite) and CaMn (CO₃)₂ (kutnahorite) has been studied up to 2 kb of PCO₂. The dolomite decomposes to CaCO₃ (ss)+MgO+CO₂ and the kutnahorite to CaCO₃ (ss)+MnO+CO₂. The kutnahorite was considered to be completely disordered (R̅₃C) near the decomposition temperature while the dolomite was found to be in ordered state at the decomposition temperature, though both were considered to stabilise with ordered structures at lower temperatures. The standard enthalpy and free energy data retrieved for the ordered dolomite is ; ΔH⁰_f = -2331.64±2.07 kJ/mol, ΔG⁰_f = -2168.59±2.07 kJ/mol., and for the disordered kutnaborite, is; ΔH⁰_f = -2093.46±3.77kJ/mol, ΔG⁰_f = -1944.80±3.77kJ/mol. The new data on dolomite are atIeast 7 kJ more negative than the earlier reported values. In the low temperature region the double carbonate field is preceded by a metastable two carbonate field of M'CO₃ (ss) and M"CO₃ (M' = Ca, M" = Mg, Mn) phases. This is considered to be the likely stage in the natural process of dolomite or kutnahorite formation.

Keywords

Dolomite, Kutnahorite, Thermodynamics, Decarbonation Curves.

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C. Srikantappa ¹, L. Venugopal ¹, J. Devaraju ¹, B. Basavalingu ¹

Affiliations
1 Department of Geology, Manasagangotri, University of Mysore, Mysore 570006, IN

Abstract

Charnockites and basic granulites occur extensively around Coorg in Western Ghats. Minor metasedimentary rocks like kyanite/sillimanite bearing gneisses and ironstone also occur. A set of late dolerite dykes cross cut all the lithologies.

The Coorg granulites record a near-peak metamorphic conditions of 720 to 760° C at pressures of 7 lo 8.6 kb. Charnockites and basic granulites contain high-density ( 1.07 to 1.09 g/cc) carbonic inclusions. Micro-textures, mineral P-T and fluid inclusion data indicate "clockwise" P-T trajectory, pointing to a relatively rapid uplift/erosion of the Coorg granulites.

Keywords

Granulites, Thermobarometry, Fluid Inclusions, Igneous Petrology, Coorg District, Karnataka.

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N. S. Krishnaraj ¹, A. S. Janardhan ¹, B. Basavalingu ¹

Affiliations
1 Department of Geology, University of Mysore, Manasagangotri, Mysore-570 006, IN

Abstract

Garnet-kyanite-sillimanite bearing pelitic and garnetiferous mafic granulites exposed at several places along the Jalsoor-Mercara and Bavali shear zones preserve evidences of deep burial of atleast 30 km. Estimation of P-T conditions of metamorphism of these granulites gives T of 725-800°C and P of 7 to 8.6 kb. Increase of pressure form core to rim in the garnet-kyanite assemblages and kyanite mantling garnet are the most significant aspects of these lithologies, suggesting long residence in the deep crust and possible thrust tectonics.

Moreover, fibrolitic sillimanite overgrowing kyanite in pelites and the developement of opx-calcic plag symplectites around garnet in the mafic rocks indicate decompression/uplift, subsequent to crustal thickening. This uplift could be part of a later event unrelated to the burial episode.

Significantly, syenite and anorthosite bodies of late Proterozoic age occur along these shear zones indicating that these lineaments were reactivated again in late Proterozoic times.

Keywords

Granulites, Jalsoor-Mercara, Metamorphic Petrology, Kanataka.

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Fareeduddin ¹, M. A. Shankara ², B. Basavalingu ², A. S. Janardhan ²

Affiliations
1 H.408, Ramesh marg, C Scheme, Jaipur 302 001, IN
2 Department of Geology, Univeisity of Mysore, Manasagangotri, Mysore-570 006, IN

Abstract

A brief account of the petrology and structure of medium grade pelitic granulites and associated charnockites occurring as slivers in the Anasagar migmatitic gneiss is given. These granulite slivers have been traced along strike up to 40 km and may cover a much wider area. Cordierite bearing pelitic granulites associated with charnockites around Chinwali were chosen for estimating metamorphic P-T conditions. The pelitic granulites are represented by the assenlblage opx-cord-gt-bio--silli-plag-k felds- qtz. Biotite-fibrolite intergrowths grow on cordierite which has opx inclusions. Garnet is often smeared with graphite. Metamorphic conditions of petite show peak pressures of 7.5 kb at 640°C. Charnockites generally record retrogressive pressure conditions of 5.7 - 4.0 kb. The mineralogy of the Chinwali granulites and P-T condition compare well with that of Sandmata granulites. The presence of these granulites, north of Ajmer, in basement migmatitic gneisses suggest the presence of an older deep crustal fragment (ca. 1.7 Ga) along the northwestern margin of the Aravalli Delhi Mobile Belt (ADMB) and belies the prevailing concepts of eastward crustal thickening and westward age polarity in the western Indian shield.

Keywords

Granulite, Charnockite, Petrology, Ajmer, Chinwali, Rajasthan.

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M. Hanuma Prasad ¹, B. Krishna Rao ², V. N. Vasudev ¹, B. Basavalingu ¹

Affiliations
1 Department of studies in Geology, University of Mysore, Mysore 570 006, IN
2 Department of Mines and Geology, 16, S.P. Complex, Lalbagh Road, Bangalore 570 027, IN

Abstract

Compositions of co-existing mineral pairs, viz., (a) cordierite- gedrite- garnet- biotite, (b) staurolite-biotite-garnet-muscovite-chlorite and (c) andalusite-staurolite-biotite-gamet in metapelites, and (d) amphibole-plagioclase pair in metabasalts of the Sandur schist belt in the eastern block of the Dharwar craton, Southern India, yield metamorphic temperatures and pressures in the range of 550°-600° C and 4-5.2 kbar, respectively. Textural relationships of the minerals in the above mineral assemblages suggest the development of cordierite, gedrite, garnet, staurolite and biotite during the main-fabric forming event (regional metamorphism). Increase in the grade of metamorphism from greenschist to amphibolite facies associated with the main deformational event is observed from the central to the peripheral portions of the belt; this can be attributed to the steep thermal gradient produced by the syntectonic granitoids. Andalusite post-dates all the other metamorphic minerals and its development outlasts the main deformational episode in the belt. Andalu∼ite is a product of thermal metamorphism, superimposed on regional metamorphism and its growth coincides with the upliftment of the terrain during the emplacement of Iate- to post-kinematic granitoids, which, under comparatively low pressure regime (∼3.75 kbar), maintained earlier peak metamorphic temperatures.

Keywords

Metamorphic Petrology, Sandur Schist Belt, Kamataka.

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B. Basavalingu ¹

Affiliations
1 Department of Studies in Geology, University of Mysore, Mysore -570 006, IN

Abstract

No Abstract.

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K. Sriramguru ¹, A. S. Janardhan ¹, Sharana Basava ¹, B. Basavalingu ¹

Affiliations
1 Department of Geology, University of Mysore, Manasa Gangotri, Mysore - 570 006, IN

Abstract

Sapphirine and kornerupine bearing assemblages in Mg-AI- rich pelites have been reported in and around the Kodaikanal hills and in the Kambam valley, forming part of the 550 Ma old Southern Granulite Terrain (SGT). Prismatine and sapphirine are found in a new association with garnet-orthopyroxene-cordierite-spinel-plagioclase-perthite bearing pelitic enclaves in granitic bodies intruding the charnockites at Rajapalaiyam, located on the southeastern slopes of the Varushanad hills and east of the Kambam valley. Prismatine with boron > 0.5 apfu is either associated with orthopyroxene or armoured by cordierite, suggesting its early formation. Association of prismatine with orthopyroxene and quartz is significant. Boron for the formation of prismatine must have come from the sedimentary protoliths, and fixed in the prismatine during fluid activity connected with earlier granulite grade metamorphism. Sapphirine bearing assemblages occur as mm-sized specks in garnetiferous granite close to the pelitic bands. This type of sapphirine is different from the general occurrence of sapphirine-orthopyroxene-cordierite forming as a breakdown product of garnet in SGT. Sapphirine bearing assemblages of SGT generally have formed during high grade, granulite facies metamorphism, with peak at 850-1000°C at P of 8.2-8.8 Kbar and with a dominant isothermal decompression path as shown by the assemblages orthopyroxene-cordierite+-plagioclaswe hich give T of 650°C at P of 6.5 Kbar. Orthopyroxene-cordierite association after garnet gives T of 900°C at P of 7.5 Kbar in Rajapalaiyam area.

Keywords

Prismatine, Sapphirine, Boron, Fluorine, Southern Granulite Terrain, Tamil Nadu.

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C. P. Sajan ¹, B. Basavalingu ¹, A. Ananda ², K. Byrappa ¹

Affiliations
1 DOS in Earth Science, University of Mysore, Manasagangothri, Mysore - 570 006, IN
2 DOS in Chemistry, University of Mysore, Manasagangothri, Mysore - 570 006, IN

Abstract

The photocatalytic degradation of Indigo Caramine dye using commercial TiO₂ and fine grained natural rutile has been carried out. The commercial TiO₂ and natural rutile were characterized using powder X-ray diffraction (XRD) and Fourier transformed infra red spectroscopy (FTIR). The study on the photodegradation of Indigo Caramine dye using commercial TiO₂ and natural rutile were investigated both under Solar and UV irradiation. The degradation of Indigo Caramine dye was checked by the following parameters like Chemical Oxygen Demand (COD), %T, irradiation time and duration. In both cases using commercial TiO₂ and natural rutile, the COD of the dye solution was reduced from 288 mg/L to less than 20 mg/L, and similarly the %T was increased from 76% to 97% and the percentage decomposition upto 97% within the irradiation duration of 3.5 hrs. The preliminary results obtained on the photodegradation of Indigo Caramine dye are highly encouraging and further work is being carried out for the use of the natural rutile or anatase sources for the other organic decomposition and treatment of industrial effluents.

Keywords

Photocatalytic Degradation, Natural Rutile, Nanominerals, Indigo Caramine Dye.

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