Refine your search
Collections
Co-Authors
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z All
Bhaduri, S. K.
- Proterozoic Rock Suites along South Purulia Shear Zone, Eastern India: Evidence for Rift-Related Setting
Abstract Views :323 |
PDF Views:3
Authors
Affiliations
1 Geological Survey of India, 27 Jawaharlal Nehru Road, Kolkata - 700 016, IN
2 Geological Survey of India, Op WB-SK-AN, Eastern Region, DK-6, Salt Lake, Kolkata - 700 091, IN
3 Geological Survey of India, Flat#4, H/31M, BP Township, Kolkata - 700 094, IN
4 Geological Survey of India, Chemical Division, Eastern Region, DK-6, Salt Lake, Kolkata - 700 091, IN
1 Geological Survey of India, 27 Jawaharlal Nehru Road, Kolkata - 700 016, IN
2 Geological Survey of India, Op WB-SK-AN, Eastern Region, DK-6, Salt Lake, Kolkata - 700 091, IN
3 Geological Survey of India, Flat#4, H/31M, BP Township, Kolkata - 700 094, IN
4 Geological Survey of India, Chemical Division, Eastern Region, DK-6, Salt Lake, Kolkata - 700 091, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 68, No 6 (2006), Pagination: 1069-1086Abstract
The South Purulia Shear Zone (SPSZ) is a part of the conspicuous -E-W to -ESE-WNW trending Tamar-Porapahar lineament. This borders the Meso-Proterozoic greenschist facies lithopackage of the Singhbhum Group (SG) comprising metasedimentaries, felsic volcanics, mafites/Ultramafites, granitoids, and alkaline/Carbonatite suite of rocks bounded by the Chhotanagpur Gneissic Complex (CGC) attaining amphibolite to granulite facies in the north CGC presumably had certatn loci of crustal weakness where pre-Rift crustal sagging led to the deposition of supracrustal rocks. Intracratonic rifting had then initiated in those pre-Existing zones of crustal weakness and troughs of the resident crust. The intracratonic basin was covered by huge volume of the felsic volcanics represented by layered tuffaceous volcaniclastic, felsic ignimbrites, crystal-Vitric tuff and tuffaceous phyllite. Meta-Greywacke has been considered as epiclastic deposit derived from felsic volcanics. The nature of welding, absence of phenocrysts typical of lava flows, parallel aligned lenticular pumice fragments exhibiting pumice-Lenticle foliation, fiamme and eutaxitic fabric and petrochemistry could imply that the felsic igniimbrite was close to welded pumiceous ash-Flow tuff having dacitic to rhyodacitic composition. Mafic-ultramafic suites of rocks in close proximity to felsic volcanics suggest a bimodal character of magmatic episode in the area Bands and lenses of tourmalinite disposed along the contact of the CGC and the SG, argued to be of volcanogenic sedimentary origin, possibly demarcates the rupture locales of a rift. The alkali-Feldspar granite(± richterite, ± aegirine-augite), syenite and carbonatites suggest tapping of deeper fractures in the rifted basin. This was coupled with the presence of granite plutonism in the setting. Geochemical signatures imply that felsic volcanics are chiefly of dacitic composition with strong LREE enrichment and narrow range of fractionation while the metabasic rock chemistry scatter in basalt to basaltic andesite field. Trace element data further corroborate 'volcanic arc granite', ' Within plate granite' and 'continental arc granite' composition for the felsic volcanics. The basin was then subscribed to compressional regime where ductile shear zones developed syn to post kinematic to F1 with the northern block (CGC) thrusting over the southern block (SG) on northerly dipping planes. Thus, an entire sequence of rifting, tourmalinite emplacement, felsic volcanism, mafic extrusion, granite plutonism, syenite/Carbonatite emplacement and sedimentation of pelites/Epiclastics during and after opening of the basin in an intracratonic setting is demonstrated. Subsequently, development of the shear zone (SPSZ) took place over the area at the close of the basin.Keywords
Ignimbrite, Dacite, Tourmalinite, Rift, Shear, Petrography, Geochemistry, Purulia, West Bengal.- Mawpyut Intrusive Complex of Jaintia Hills District, Meghalaya, Northeastern India: A Case Study for Magmatic Differentiation
Abstract Views :192 |
PDF Views:0
Authors
Affiliations
1 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata - 700 019, IN
2 Geological Survey of India, Eastern Region, Salt Lake City, Kolkata - 700 091, IN
1 Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata - 700 019, IN
2 Geological Survey of India, Eastern Region, Salt Lake City, Kolkata - 700 091, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 74, No 3 (2009), Pagination: 385-394Abstract
The petrological details of the ultramafic-mafic-alkaline complex related to Sylhet Trap occurring near to Mawpyut (25°25'N:92°10'E) of Jaintia hills district Meghalaya, northeastern India, are poorly known. Field investigations indicate that the Mawpyut body occurs as a pluton distinctly intrusive into adjacent low grade metasedimentary Shillong Group of rocks. This body reveals development of two broad lithotypes namely ultramafic (olivine clinopyroxenite, clinopyroxenite and plagioclase bearing ultramafic) and mafic (mostly gabbro, orthopyroxene gabbro, olivine gabbronorite, mela gabbro and mela-gabbro-norite) with minor presence of later syenitic veins. Though, in general, the pluton shows mineralogical variations, the field boundaries among those petrographic types are not discernible. Careful consideration of major and trace element chemistry of the constituent lithomembers clearly suggest progressive insitu fractionation of a common parent magma.Keywords
Sylhet Traps, Mawpyut Complex, Major and Trace Element Characters, Differentiation History, Meghalaya.References
- BAKSI, A.K. (1995) Petrogenesis and timing of volcanism in the Rajmahal flood basalt province, Northeastern India. Chem. Geol., v.121, pp.73-90.
- CHEN, Y. and ZHANG, Y. (2008) Olivine dissolution in basaltic melt. Geochim. Cosmochim. Acta, v.72, pp.4756-4777.
- CLASS, C., GOLDSTEIN, S.L., GALER, S.J.G. and WEISS, D. (1993) Young formation age of a mantle source. Nature, v.362, pp.715-721.
- HANSON, G.N. (1978) The application of trace elements to the petrogenesis of igneous rocks of granitic composition. Earth Planet. Sci. Lett., v.38, pp.26-43.
- KUMAR, D., MAMALLAN, R. and DIWEDY, K.K. (1996) Carbonatite magmatism in north east India. Jour. Southeast Asian Earth Sci., v.13, pp.145-158.
- KUO, L.C. and KIRKPATRICK, R.J. (1985) Kinetics of Crystal Dissolution In The System Diopside-Forsterite-Silica. Amer Jour. Sci. v.285, pp.51-90.
- KUSHIRO, I. (1964) The system Diopside - Fosterite - Enstatite at 20 kilobars. Pap. Geophys. Lab. Carnegie Institution, Washington, v.63, pp.101.108.
- MAHONEY, J.J., MACDOUGALL, J.D., LUGMAIR, G.W. and GOPALAN, K. (1983) Kerguelen hotspot source for the Rajmahal Traps and Ninetyeast Ridge? Nature, v.303, pp.385-389.
- MAITRA, M., BHADURI, S.K. and PANT, N.C. (2003) Ultramaficmafic rock ensemble of Mawpyut, Jaintia Hill district, Meghalaya . A preliminary account. Indian Minerals, v.57, no.1&2, pp.75-84.
- MAZUMDER, S.K. (1986) The Precambrian framework of part of the Khasi Hills, Meghalaya. Rec. Geol. Surv. India, v.117, no.2, pp.1-58.
- NANDY, D.R. (2001) Geodynamics of North-Eastern India and the adjoining region. acb Publication, Calcutta, 209p.
- SAHA, A.K. (1959) Emplacement of three granitic plutons in Southwestern Ontario. Bull. Geol. Soc. Amer., v.70, pp.1293-1325.
- SARKAR, A., DATTA, A.K., PODDAR, B.K., BHATTACHARYA, B.C, KOLLAPURI, V.K. and SANWAL, R., (1996) Geochronological studies of Mesozoic igneous rocks from Eastern India. Jour. South East Asian Earth Sci., v.13(2), pp.77-81.
- SRIVASTAVA,R.K . and SINHA, A.K. (2004) Geochemistry of Early Cretaceous alkaline ultramafic-mafic complex from Jasra, Karbi Anglong, Shillong plateau, northeastern India.Gondwana Res., v.7, pp.549-561.
- STRECKEISEN, A. (1976) To each plutonic rock its proper name. Earth Sci. Rev., v.12, pp.1-33.
- THORNTON, C.P. and TUTTLE, O.F. (1960) Chemistry of igneous rock. I Differentiation Index. Amer. Jour. Sci.,v.258, pp.664-684.