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Mitra, S.
- Cavity-Filling Kyanites from Sukinda, Cuttack District, Orissa
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 13, No 2 (1972), Pagination: 172-174Abstract
No Abstract.Full Text
- Some Uncommon Phenomena in Ptygmatic Structures
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 18, No 11 (1977), Pagination: 577-588Abstract
In ptygmatic structures formation of' clods' at the nodes of folds and fragmentation of the ptygma are common features. A rheological model has been set-up to generate such structural elements by considering the deforming vein to be elastic-plastic and embedded in a Newtonian viscous matrix. Because of elastic-plastic character, some regions of the vein will flow elastically and some plastically. Flow of paths of these generate complicated flow lines and with progressive deformation the vein tears off along these lines. Ptygmatic field structures have been classified and their modes of generation discussed.
- Geothermometry and Mineralogy of Two-Pyroxene Granulites: Evaluation from Mossbauer and X-ray Single Crystal Cation Partitioning of Ca-Poor and Ca-Rich Pyroxenes
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta - 700032, IN
2 Dipartimento di Scienze della Terra, Trieste University, Via Weiss 8, 34127 Trieste, IT
3 Department of Geology, Yonsei University, Seoul 120-749, KP
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 53, No 5 (1999), Pagination: 537-548Abstract
Fe-Mg ordering as well as Fe2+ and Fe3+ distribution at different sites in coexisting orthopyroxene and clinopyroxene determined by, Mossbauer spectrpscopy and X-ray diffraction (sample 6a), have been used in deciphering the thermal history of two-pyroxene granulites of Sittampundi Complex (India). Orthopyroxenes and clinopyroxenes are compositionally in the granulite field of metamorphism. For orthopyroxenes, the Mossbauer spectra show that Fe2+ is present at M1 and two different M2 sites, while Fe3+ is localised at M1 site alone. For the coexisting clinopyroxenes, Fe2+ occurs at both M1 and M2. Fe3+ is present only at M1 site, but in Ca-rich clinopyroxenes, under high fO2, conditions, it is seen to replace silicon in tetrahedral site.From the distribution of Fe2+ - Mg, using Mossbauer data, the blocking temperature of intracrystalline ordering in orthopyroxene has been calculated to range between 427 and 699°C, in agreement with the estimated temperature obtained by means of X-ray data of about 500°C; in clinopyroxene it was 680°C as obtained from X-ray data. The recorded inter-crystalline ordering temperature was determined as between 661 and 785°C. The lowering of blocking temperature recorded by intracrystalline Fe2+ - Mg exchange suggests that the cation ordering in the M1 and M2 sites continued in the cooling path of the granulites below the temperature indicated by inter-crystalline distribution, and that the cooling (history) suffered by the host rocks was slow.