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

S. K. Acharyya ¹

Affiliations
1 Geologlical Survey of India, Calcutta -700 016, IN

Abstract

No Abstract.

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S. K. Acharyya ¹, Abhinaba Roy ²

Affiliations
1 Geological Survey of India, 27, Jawaharlal Nehru Road, Calcutta - 700 016, IN
2 Central Region, Seminary Hills, Nagpur - 440 006, IN

Abstract

Central Indian Tectonic Zone (CITZ), which divides the Indian subcontinent into Bundelkhand Block in the north and the Deccan Block in the south, is represented by a collage of different lithotectonic terranes ranging in age from Archaean to Recent. It comprises two parallel structural domains, namely the Son-Narmada (SONA) subzone in the north and the Sausar mobile belt (SMB) in the south. The ancestry of the SONA subzone is indicated by the Neoarchaean - Palaeoproterozoic ages yielded by the rocks of Mahakoshal fold belt; the Sausar belt, on the other hand, has yielded Meso- to Neo-proterozoic ages. The present response of CITZ to accumulation of stress and attendant seismicity is governed by the structures generated due to early tectonic history of rocks within it, particularly the development of number of E-W to ENE-WSW striking, brittle and ductile shear zones. While the Sausar belt has remained more or less stable since the late Precambrian, the SONA and Tapti lineament zones have been reactivated several times. Two prominent ENE-WSW trending deep fautts, termed the Son-Narmada North Fault (SNNF) and Son-Narmada South Fault (SNSF) have been episodically active from Neoarchaean onwards. The SNSF in particular has witnessed protracted reactivation well into the Phanerozoic. Intraplate seismicity in continents is commonly concentrated along ancient fault zones. Reactivation of faults or shear zones is favoured over new fault generation, since the SNSF is in a high shear stress orientation. Although the Sausar mobile belt is marked by a number of E-W trending parallel ductile shears, mass transfer processes such as silicification, recrystallization and grain growth during Precambrian appear to have healed them.

Keywords

Structural Geology, Seismology, Tectonothermal History, Central Indian Tectonic Zone (CITZ), Maharashtra, Madhya Pradesh.

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S. K. Acharyya ¹, J. R. Kayal ¹, A. Roy ¹, R. K. Chaturvedi ¹

Affiliations
1 Geological Survey of India, 27, J. L. Nehru Road, Calcutta - 700 016, IN

Abstract

Macroseismic and microseismic (aftershock) investigations were carried out by the Geological Survey of India immediately after the Jabal pur earthquake (M 6.0) of May 22, 1997. The meizoseismal area of an intensity VIII (MSK) is 35 km long and 15 km wide, trending ENE-WSW. The aftershock investigation was earned out by a five-station temporary microearthquake (MEQ) network. Five felt aftershocks (M≥3.0) and 23 aftershocks in the magnitude range 1.5 to < 3.0 were recorded by the network. These are mostly clustered in an elongated area, 15 ×10 krn, near the main shock epicentre. and occurred at a depth range 35-40 k.m which is compatible with that of the main shock. The fault-plane solution of the main shock and the aftershocks revealed reverse faulting with left-lateral strike-slip component The hypocentral section and the fault-plane solutions indicate that the pre-existing ENE-WSW trending Nannada South Fault is deep-ischolar_mained to mantIe depth, and has been activated at the crust-mantle boundary to produce the main shock and the aftershocks. The failure appears to be caused in response to the northward post collisional movement of the Indian plate.

Keywords

Earthquake, Aftershocks. Microseismicity, Fault-Plane Solution, Jabajpur, Madhya Pradesh.

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S. K. Acharyya ¹, K. K. Ray ¹, D. K. Roy ¹

Affiliations
1 Geological Survey of India, Calcutta, IN

Abstract

The oceanic pelagic sediments from the ophiolite assemblages of Naga Hills (NHO) and Andaman islands (ANO) broadly correspond to Late Cretaneous to Paleocene age. Late Cretaceous ocean floor represented in ANO was dominantly below the carbonate-compensation-depth (CCD), whereas it was uneven but mainly above CCD during Paleocene-Early Eocene. Maestrichtian to Paleocene ocean floor appears to be dominantly above the CCD in NHO. The NHO and ANO have closely similar postemplacement ophiolite-derived mid- and mid-late Eocene cover sediments respectively. Emplacement of the Naga Hills ophiolites during mid-Eocene, was possibly caused due to initial collision of an ocean-island chain with the subduction zone beneath the Central Burmese continent. Emplacement of the Andaman ophiolites occurred during early-mid-Eocene and may have been caused by a similar situation. The Chin Hills ophiolites were also mainly emplaced during early Eocene. The accreted ophiolites of the Indo-Burman range and Andaman islands were thrust westward over the Paleogene turbidite pile, deposited on the down going Indian plate during late Oligocene, due to terminal India-Burma continent-continent collision. In the southern Manipur sector of Naga Hills, the olistostromal upper Disang Formation (mid to late mid-Eocene) tectonically flooring the NHO, stratigraphically underlies the flyschoid to molassic Barail (Oligocene) sediments. In Andaman islands, the Lipa Formation with early Eocene and older olistoliths, forms the dominant constituent of the lower tectonic sedimentary melange flooring the ophiolites. Towards west, the sedimentary melange overrides the Archipelago Group. (Neogene) which unconformably overlies the Andarnan Flysch of Eocene-Oligocene age. The ischolar_main-zone of the collisional suture appears to be concealed below younger sediments in the Central Burma basin and in the Andaman Sea, parts of the latter being created as a back-arc marginal basin. There is thus no straightforward relation between the Late Oligocene collision suture and the present subduction zone along the trench to the west of Andaman-Nicobar islands.

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D. P. Das ¹, P. K. Raha ¹, S. K. Acharyya ¹

Affiliations
1 Geological Survey of India, Calcutta 700016, IN

Abstract

Two tiny carapaces having strong resemblance to Ostracoda are reported from the basal part of the upper Krol Formation occurring in the Nainital Synform of U. P. Himalaya. These ostracode forms are present in close association with several forms of shelly microfauna distinctive of Tommotian (early Cambrian) time. The characteristic features of these two forms representing the oldest ostracodes of the Indian subcontinent are described.

Keywords

Palaeontology, Ostracoda, Krol Formation, Nainital, Kumaun Himalaya.

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S. K. Acharyya ¹

Affiliations
1 Geological Survey of India 27, Jawaharlal Nehru Road, Calcutta 700 016, IN

Abstract

No Abstract.

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S. K. Acharyya ¹, B. P. Singh ², J. S. Pawar ², Mithila ²

Affiliations
1 Dept Geol. Sci. , Jadavpur Univ , Kolkata - 700032, IN
2 Postgraduate, Department of Geology, University of Jammu, Jammu - 180 006, IN

Abstract

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S. K. Acharyya ¹

Affiliations
1 15, Dr. Sarat Banerjee Road Kolkata - 700 032, IN

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S. K. Acharyya ¹, B. S. Bisht ²

Affiliations
1 Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN
2 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad- 500 016, IN

Abstract

No Abstract.

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S. K. Acharyya ¹

Affiliations
1 West Bengal Academy of Science and Technology, 4, Raja S.C. Mullick Road Kolkata - 700 032, IN

Abstract

No Abstract.

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S. K. Acharyya ¹

Affiliations
1 Geological Survey of India, 27, Jawaharlal Nehru Road, Calcutta 700 016, IN

Abstract

No Abstract.

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S. K. Acharyya ¹

Affiliations
1 Department of Geology, Jadavpur University, Kolkata - 700 002, IN

Abstract

No Abstract.

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Puspendu Saha ¹, S. K. Acharyya ², V. Balaram ³, Parijat Roy ³

Affiliations
1 Department of Geology, ETL, University of Calcutta, 35, Ballygunge Circular Road, Kolkata - 700 019, IN
2 Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN
3 Geochemistry Division, CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, IN

Abstract

Geochemistry of Tuting metavolcanic rocks is being reported for the first time. Narrow slivers of mafic volcanic rocks, as those at Tuting, also occur in close association with slivers of more complete sections of ophiolites at the Tsangpo river section upstream of Tuting and skirt round the Namche Barwa antiform. These detached slivers of the mafic volcanic rocks and the ophiolites represent the easternmost components of the Yarlung Tsangpo Ophiolite, and also define the arcuate shape of the Eastern Himalayan syntaxis. The metavolcanic rocks exposed at the apex of the Siang river dome at Tuting (Tsangpo River named Siang down stream of Tuting) is the only exposure of such rocks from the Himalayan syntaxial area in India.

The Tuting metavolcanic rocks correspond to andesite and basaltic andesite as per TAS diagram. The mobility of major elements possibly has affected their classification. As per Zr/TiO₂ - Nb/Y diagram of Winchester and Floyd (1977), proposed for classification of altered igneous rocks, the Tuting samples mainly correspond to 'sub-akaline basalt' and one sample plot as 'andesite/basalt'. These have a flat chrondrite-normalised REE pattern. MORB-normalized multi-elemental plot shows enrichment in large ion lithophile (LIL) and the light rare earth elements (LREE), and depletion in several high field strength elements (HFSE). Based on these trace element patterns and a few discrimination plots, the Tuting metavolcanic rocks are inferred to have generated in supra-subduction zone environment in an intra-oceanic arc, back arc setting, or in a mid-ocean ridge process that resembles the Chile Ridge spreading centre.

Keywords

Tuting Metavolcanics, Ophiolite, Geochemistry, Siang Dome, Eastern Himalayan Syntaxis.

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