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Guha, Dipayan
- Petrochemistry of Piemontite-Bearing Assemblages in Calc-Silicate Rocks from Sausar Group, India
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Authors
Affiliations
1 Department of Geology, Kyushu University, Fukuoka, JP
2 Department of Geological Sciences, Jadavpur University, Calcutta 700032, IN
1 Department of Geology, Kyushu University, Fukuoka, JP
2 Department of Geological Sciences, Jadavpur University, Calcutta 700032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 36, No 4 (1990), Pagination: 403-412Abstract
Piemontite-garnet bearing assemblages with or without braunite, occur in calc-silicate rocks in Sausar Group, India. The studied assemblages equilibrated under similar physical condition of metamorphism, at a high fO2 regime. Chemically both piernontite and garnet are enriched in Mn in braunite-bearing assemblages, as compared to the braunite-free ones. petrographic features show that garnet+calcite±hematite are the late overprints in these assemblages, derived through a devolatilization reaction involving piemontite+precursor carbonate+quartz±braunite. The study shows that in the braunite-bearing assemblages, the 'maximum' Mn3+ content of the piemontite was not dictated by the mere presence of braunite, but it is rather correlatable with the modal abundance of braunite. Further, the XMn3+ in the piemontite and the modal abundance of braunite have a direct relationship with Al/Mn, Mn/Al+Si and Si/Al) ratios in the bulk composition of the assemblages. In the present situation the Al-Mn3+-Fe3+ distribution coefficients amongst equilibrating piemontite-garnet pairs show strong dependence on the bulk chemical composition.Keywords
Geochemistry, Calc-Silicate Rocks, Piemontite, Sausar Group, Madhya Pradesh.- Alkali Basalt of Kachchh: its Implication in the Tectonic Framework of Mesozoic of Western India
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Authors
Affiliations
1 Geochronology and Isotope Geology Division, Geological Survey of India, 15 A & B, Kyd Street, Kolkata - 700 016, IN
2 Geological Survey of India, Operation Gujarat, Gandhinagar - 382 093, IN
3 Central Petrological Laboratories, Geological Survey of India, 15 A & B, Kyd Street, Kolkata - 700 016, IN
1 Geochronology and Isotope Geology Division, Geological Survey of India, 15 A & B, Kyd Street, Kolkata - 700 016, IN
2 Geological Survey of India, Operation Gujarat, Gandhinagar - 382 093, IN
3 Central Petrological Laboratories, Geological Survey of India, 15 A & B, Kyd Street, Kolkata - 700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 66, No 5 (2005), Pagination: 599-608Abstract
Field evidences in Kachchh show that alkali basalts occur as flows over Mesozoic sediments. The top parts of Mesozoic Bhuj Sandstone often carry scoria and lapilli related to alkali basalt magmatism indicating that alkali magmatism and sedimentation went side by side. Tholente flows occur as blanket over both Mesozoic sediments and alkali basalt bodies.Evidences are provided to show that alkali basalt magmatism in Kachchh was not only an earlier episode than tholente emplacement, it also predates the closing of Kachchh Mesozoic basin and seems to support a protracted period of Deccan magmatism (70 - 60 Ma). The study also shows that huge concentration of alkali basalt in the western Kachchh mainland is associated to a zone of transtension related to the rifting of Kachchh basin. Alkali basalt bodies and whole of Mesozoic sequence were affected by reverse faults related to closure of Kachchh basin with development of series of hanging wall anticlinal and footwall synclinal structures.
Keywords
Alkali Basalt, Tholente, Flow, Plug, Releasing Bend, Kachchh.- Ultrapotassic Post-Collisional Dyke from the Ladakh Batholith, Northwest Himalaya
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PDF Views:161
Authors
V. Ravikant
1,
Dipayan Guha
2
Affiliations
1 G&IG Division, Geological Survey of India, Kolkata - 700 016, IN
2 D.D.G.(CGL) Cell, Geological Survey of India, Kolkata - 700 016, IN
1 G&IG Division, Geological Survey of India, Kolkata - 700 016, IN
2 D.D.G.(CGL) Cell, Geological Survey of India, Kolkata - 700 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 59, No 5 (2002), Pagination: 473-476Abstract
We report here petrographic and bulk geochemical characters of an ultrapotassic dyke from the Ladakh batholith, NW Himalaya, for the first time, and attempt to compare it with similar dykes from SW Tibet which are typical of post-collisional magmatism. Postcollisional shoshonitic and ultrapotassic dykes have been reported from north Karakoram (Pognante, 1990) and potassic and ultrapotassic lavas from SW Tibet by Miller et al. (1999). They have been linked to large scale tectonic reactivation involving the lithospheric mantle during the continued India-Eurasia collision since ∼50 Ma.- New Record of Sauropod Nest-Sites in Lameta Formation from Jhalod, Panchmahals District, Gujarat
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Authors
Affiliations
1 Operations Gujarat, Geological Survey of India, Gandhinagar, IN
1 Operations Gujarat, Geological Survey of India, Gandhinagar, IN