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P. Kumar ¹, N. N. Pandey ¹, N. Okendro Singh ², N. Chandra ³, D. C. Mishra ³, P. K. Agrawal ³, A. Barat ¹, J. C. Bhatt ³

Affiliations
1 Directorate of Coldwater Fisheries Research (ICAR), Bhimtal-263 136, Nainital (Uttarakhand), IN
2 College of Agriculture, Central Agricultural University, Iroisemba - 795 004, Imphal, Manipur, IN
3 Vivakanand Pravatiya Krishi Anusandhan Sansthan (VPKAS), Almora (Uttarakhand), IN

Abstract

An experiment on rearing of common carp was carried out in three types of ponds viz. earthen pond, cemented tank and poly tank at field centre, DCFR, Champawat (Uttarakhand) and at selected farmers field of Champawat District to evaluate the growth performance of this fish species. ANCOVA results revealed that there are three distinct seasons which influence on length-weight relationship of common carp culture in these pond systems. The fish follows isometric growth in spring season (March-May); (however it does not follow in the remaining seasons). Further, there is no specific growth pattern of common carp observed in these pond environment. Logistic curve is the best fitted model to the dataset obtained from cemented pond. However, Richards and von-Bertalanffy curves are found appropriate to represent the growth pattern of this fish in earthen and poly tank, respectively. In the long run, higher growth of fish is predicted in poly tank.

Keywords

Poly Tank, Formulated Diet, Length-weight Relationship, Isometric Growth

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D. C. Mishra ¹, Hari Narain ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN

Abstract

The airborne magnetic case history from Central India presented here provides indications regarding following concealed geological structures: (i) a deep-seated structure oblique to Narmada-Son lineament at a depth of nearly 4800 feet (below Vindhyan sediments). (ii) a subsurface basic intrusion similar to volcanic plug located at a depth of nearly 4900 feet (below Vindhyan sediments). (iii) extension of Bijawar rocks underneath Vindhyan sediments.

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D. C. Mishra ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad 500 007, IN

Abstract

The satellite magnetic data (MAGSAT) over India is analysed with reference to the major tectonic elements of the country. The recorded magnetic anomaly varies from +6 gamma over the eastern part of the Indian shield to -9 gamma over the Himalayas. Deccan Trap is characterized by 'nosing' of the magnetic contours. Tibet plateau and Shillong massif show distinct magnetic anomalies. The magnetic crust derived from this data depicts a variation from 30 km under the Cambay basin and the western part of the Narmada-Son lineament to 40 km under the Aravallis and 42 km under the-Singhbhum and the Dharwar cratons. The general thickness of the magnetic crust under the Himalayas is 35-36 km with a thickening of 2-4 km under the Tibet plateau and the Shillong massif.

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D. C. Mishra ¹, S. B. Gupta ¹, M. B. S. V. Rao ¹, M. Venkatarayudu ¹, G. Laxman ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad 500007, IN

Abstract

Detailed gravity and magnetic surveys in and around the Godavari basin have helped in delineating the subsurface structures which, in turn, facilitated reconstructing its evolution. The general NW-SE trend of the magnetic and the gravity anomalies towards north takes a swift turn along an E-W line south of Bhadrachalam. This may be attributed to a deep-seated fault dividing the basin into Godavari and Chintalapudi sub-basins. The same fault may be responsible for limiting the southern extent of Pakhal sediments. A similar deep-seated fault north of Bhadrachalam along the Mailaram 'high' is also indicated. Modelling of some critical gravity and magnetic anomalies indicates the maximum thicknesses for Gondwana and Sullavai sediments as 4.5-5 km and 1.5-2 km respectively. A large gradient in the Bouguer anomaly on the eastern side of the Gondwana basin suggests the existence of a long continuous normal fault which is the master fault of the Gor.dwana rift valley. The other side of the basin is characterised by variations in the gradient of the Bouguer anomaly suggesting enechelon faulting.

The Gondwana basin is flanked on either side by heavy rocks of density 2.95 g/cm³ between the depths of 6km to 13 km which might be due to the block uplift of the lower crust forming the 'shoulders' of the rift valley or large sub-basic intrusions in the region. The definite magnetic anomalies in this region providing a high susceptibility of 0.1-0.2 emu almost at the same depth as obtained from the Bouguer anomaly further substantiate them. The subsequent uplifts of the basin is apparent from 'highs' in Bouguer anomaly inside the basin such as around Chinnur which shows sharp gradients on either side suggesting faulted margins. The Regional Bouguer anomaly separated from the observed field along a few representative profiles suggests the presence of a high density (3.1 g/cm3) material along the Moho between the depths of 30km to 38km.

The magnetic data reveals several basement ridges and intrusions as far west as. Manthani and Sirpur-Kagaznagar which are transverse to the general trend of the Gondwana basin and almost parallel to the eastern ghat trends suggesting that they may be the subsurface reflections of eastern ghat orogeny. A well-defined magnetic anomaly in the Chintalapudi sub-basin suggests the depth to the basic intrusion in the basement as 3.1 kilometres. There are high magnetic anomalies along the Precambrian faults defining the Purana basin suggesting basic intrusions along them. The basin as a whole depicts a high heat flow specially its southern part which might be due to several intrusive bodies as inferred from the magnetic and the gravity studies. The Godavari basin is a typical rift structure formed during the Gondwana period. The high density material along the Moho and in the upper crust suggests the diapiric upwelling of the asthenosphere as the main cause for the development of a typical continental graben in this region and subsequent uplifts along the shoulders.

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D. C. Mishra ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad 500007, IN

Abstract

Regional Bouguer anomaly over the Deccan Trap (south of Poena) is modelled, constraining it from Deep Seismic Sounding (DSS) studies. A regional, based on the normal Moho obtained from DSS studies along a profile, provides a broad 'hump' over the trap. The residual Bouguer anomaly consists of 'lows' which are modelled in the form of undulations of the Moho (37-41 krn) and Conrad (17-21 km) discontinuities and their rise towards the coast conforming with the DSS studies. These depressions of the Moho and Conrad discontinuities coincide with high plateaus on the surface on either side of river Bhima suggesting them to be caused by local isostanc compensation. The broad regional hump is attributed to the high density inhomgeneities in the upper mantle, approximately at a depth of 130-200 krn which also seem to be reflected in higher P-wave residuals in the teleseismic experiments conducted in this region. It is suggested that this upper mantle inhomgeneity could be due to the erosional unloading of the Deccan traps dod may represent some form of regional compensation. Therefore, two kinds of compensation are basically suggested in this region, namely, local in the form of variations in the level of the lower crust and regional in the form of high density mhomogeneity in the upper mantle. This analysis, therefore, does not support the suggestion of the existence of any sediment-filled rift valley under the traps in this region.

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L. K. Das ¹, D. C. Mishra ², D. Ghosh ¹, B. Banerjee ¹

Affiliations
1 Central Geophysics Division, Geological Survey of India; P-49; C II Road, Beliaghata, Calcutta-700 016, IN
2 National Geophysical Research Institute, Hyderabad-500 007, AP, IN

Abstract

Ground magnetic survey of part of central India covering the Vindhyan Basin of the upper Son valley region has delineated some subsurface vsolcanogenic Proterozoic rifts below the Vindhyan cover and several faults which have controlled the tectonics of the region. The magnetic map in general shows four distinctly different domains with magnetic anomalies differing both in amplitude and their nature. In general, the Vindhyan basin is characterized by low amplitude broad anomalies while the Mahakoshal (lower Proterozoic) Group depicts large amplitude sharp anomalies due to the presence of high susceptibility (2-19 × 10^-3 CGS units) ferruginous rocks in them. The domain boundaries are either faults or indicate formational contacts between the different types of rocks with contrasting susceptibility values.

The subsurface basement relief map of the Pre-Vindhyan topography determined by 2-dimensional Harmonic Inversion of the magnetic data reveals an asymmetric graben structure with the southern boundary fault between the Vindhyans and the Mahakoshals as the most prominent linear structure.

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H. C. Tewari ¹, V. Divakar Rao ¹, B. L. Narayana ¹, M. M. Dixit ¹, N. Madhav Rao ¹, A. S. N. Murty ¹, B. Rajendraprasad ², P. R. Reddy ¹, N. Venkateswarlu ¹, V. Vuaya Rao ¹, D. C. Mishra ¹, S. B. Gupta ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500007, IN
2 National Geophysical Research Institute, Hyderabad-500007

Abstract

Lithological, gravity, magnetic, and seismic data within 100 Km corridor of the 400 km long seismic reflection profile are compiled to constitute the NW-SE Nagaur-Jhalawar Geotransect. The transect sequentially cuts across the Neo-Proterozoic Marwar Basin (MB) on the northwest, the Palaeo/Mesoproterozoic Delhi Fold Belt (DFB), the middle/late Archaean Bhilwara Gneissic Complex (BGC) and the MesolNeoproterozoic to early Palaeozoic Vindhyan Basin (VB) at the southeast. The BGC and DFB belts show polyphase deformation and metamorphism.

The BGC within the transect, consists of Sandmata Granulite Complex, followed by amphibolite facies Mangalwar Complex and Greenschist facies Hindoli/Sawar groups. The BGC show evidence of crustal reworking at c.3.0 Ga. The DFB is represented by amphibolite facies metavolcanic-metasedimentary shallow marine sequences and is tectonically highly disturbed. The DFB deposits (c. 2.0 - 1.5 Ga.) were subjected to tectonic deformation during Delhi orogeny (c. 1.5 Ga.), which is marked by syntectonic granitic plutonism. Both, the BGC and OFB also appear to have been affected by Neoproterozoic thermal events and granitic plutonism. The Neoproterozoic MB consists of clayevaporite sequences of shallow oscillatory basin deposits.

Seismic, gravitylmagnetic and magneto-telluric techniques could delineate a number of shallow to deep faults, intrusive bodies and a high conductivity zone. The total magnetic intensity shows a regional increase towards southeast. The Bouguer anomaly values show a steep rise of upto 80 mGal towards the boundary of OFB and BGC. Based on the seismic studies, doubling of the crust under the OFB and vertical intrusion of high density material under the BGC are inferred. The upper crust is, in general, transparent in its reflectivity while the lower crustal reflectivity is high in the transect area, except in the BGC and the VB. A thrust boundary, dipping NW, is present at the eastern margin of the BGC and could be traced up to 30 km depth. The Moho is at a depth of 36-38 km under the MB. Multiple Moho reflections are identified in the DFB crust, the deepest being at 45-50 km depth. In some part of the BGC the Moho can not be identified but in parts it is traced at about 50 km depth, with southeast up dip, before becoming subhorizontal at depth of 41-42 km. It becomes shallower to about 30 km depth at the SE end under the VB.

Keywords

Delhil Aravalli Fold Belt, Geotransect, Northwest India.

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D. C. Mishra ¹, S. B. Gupta ¹, M. R. K. Prabhakar Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500007, IN

Abstract

Airborne total intensity magnetic survey flown at a height of approximately 152 m in central India has delineated several linear magnetic anomalies of 200-400 nT aligned together to form a large magnetic lineament approximately 1 km wide and 100 km long. The nature of magnetic anomalies suggest the lineament to be a fracture zone with basic intrusives at places. Magnetic and resistivity surveys on ground provide large magnetic (600-800 nT) and low resistivity anomalies along this lineament suggesting a fracture zone with basic intrusive rocks at places and very good groundwater potentiality along it.. Existing wells close to the lineament yield good amount of water, while those away from it show poor yield. Water table contour map of the area shows contours parallel to the lineament indicating pumping of more water from this zone causing lateral flow of groundwater.

This lineament does not find reflection in the ground gravity survey; instead it delineated some second order small dome and basin structures around Damoh and Jabera which are not recorded in the airborne total intensity map referred to above. This suggests that while linear features are better reflected in the airborne magnetic surveys small-scale three-dimensional basement structures are better reflected in the ground gravity surveys. This indicates the need for an integrated airborne and ground exploration programme for delineating subsurface structures/tectonics and to quickly assess the groundwater resources of a region.

Keywords

Geophysics, Groundwater, Linear Structures, Magnetic Anomaly, Electrical Resistivity, Vindhyan Basin.

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Harsh K. Gupta ¹, T. Harinarayana ¹, M. Kousalya ¹, D. C. Mishra ¹, Indra Mohan ¹, N. Purnachandra Rao ¹, P. S. Raju ¹, B. K. Rastogi ¹, P. R. Reddy ¹, D. Sarkar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

No Abstract.

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D. C. Mishra ¹, A. P. Singh ¹, M. B. S. Vyaghreswara Rao ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad 500007, IN

Abstract

The Idukki earthquake with epicentre around Nedumkandam, approximately 20 km east of the Tdukki reservoir, has been in the news. A detailed gravity profile from Bangalore to Trivandrum across Cardamom-Palni hill ranges has delineated a fault type of anomaly coinciding with the epicentre of the earthquake whose modeHing suggests a shallow fault extending up to 10-11 km. This feature being associated with a thick crust in this region controlled by deep faults might have got reactivated to cause this earthquake.

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D. C. Mishra ¹, R. P. Rajasekhar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-7, IN

Abstract

Gravity highs surrounding Bundelkhand Craton and three sets of sub parallel paired aeromagnetic anomalies along its SE margin are attributed to High-Density, high susceptibility volcano sedimentary sequences and mafic intrusives of Bijawar Group of rocks of Paleo-Proterozoic period. Modelling of airborne magnetic anomahes provide almost vertical intrusives of high susceptibility (1 x 10^-3emu) mafic rocks at a depth of about 850m below northern margin of Vindhyan sediments in the basement which is supported from high velocity rocks at the same depth in an adjoining seismic section. Both these anomalies are typical of those observed along rifted continental shelves world over as in case of western margin off India, Norway, Red Sea Rift, etc.

Gravity highs and linear magnetic anomalies along southern margin of the Vindhyan basin are attributed to mafic and ultramafic intrusives of older Mahakoshal group of rocks with volcano sedimentary sequences of sectoral nature at the rifted margin of Bundelkhand craton similar to canyon deposits along present day continental rise and slope. The undisturbed Vindhyan sediments of Meso-Neo-Proterozoic period were deposited on the platform provided by continental shelf of Bundelkhand craton during convergence as fore land basin. This is in conformity with relative ages of Mahakoshals, Bijawars and Vindhyan sediments as they formed during rifting and convergence phases, respectively. Volcanic plugs (~1.11 Ga) associated with northern margin of Vindhyan basin (Panna diamond belt) and Mahakoshal Group of rocks (Jungel pipes) towards the south lying with in zones of high magnetic anomahes (mafic/ultramafic rocks referred to above) might be related to the same rifting process, but extruded to surface at later dates. Gravity high east of Aravalli Delhi Mobile Belt forming the Agra-Shahjahnpur ridge bounded by northward extensions of Great Boundary Fault and Chambal fault, is attributed to rocks equivalent to Mahakoshal Group of rocks along the western margin of the Vindhyan basin extending under the Ganga basin up to the Himalayan front in Western Nepal where seismically active zone of Western Himalaya starts.

Keywords

Bundelkhand Craton, Vindhyan Basin, Bijawar and Mahakoshal Group of Rocks, Rifted Margins.

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D. C. Mishra ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

The geoid corrected Bouguer anomaly map of India presents linear gravity highs along (I) the Aravalli-Delh Fold Belt (ADFB), (II) the Satpura Fold Belt (SFB), (III) the Eastern Ghat Fold Belt (EGFB), (IV) the Shear Zone (SZ) between the Western and the Eastern Dharwar Cratons (WDC and EDC) (v) the Transition Zone (TZ) between Dharwar Craton and the Southern Granulite Terrain(SGT) and (vi) the Cauvery Shear Zone (CSZ) between Moyar-Bhavani and Palghat-Cauvery Shear Zones (MBSZ and PCSZ) in SGT. Gravity highs over the relatively younger Proterozoic fold belts are accompanied by gravity lows over adjoining older Archaean cratons, which are primarly attributed to granite plutons and/or crustal thickening. The gravity high observed over the ADFB is related to domal shaped high density and high velocity body in lower crust under Delhi Supergroup of rocks (1 45 Ga) whch is suggestive of an extensional regime giving rise to rift basins/Aulacogens. The accompanying gravity low towards the west is related to K-Granite plutons and intrusives( 0 8-0 75 Ga) associated with back arc type basins, which along with subsurface extent and shape of exposed ophiolites and granulite rocks in gravity model suggest compression and thrusting from west to east and presumed subduction from east to west during Meso-Neoproterozoic period in this section. Geophysical signatures of paired gravity anomaly with gravity high related to high density, high velocity and high conductivity lower crustal mafic rocks in upper crust under the SFB and large wavelength gravity low to low density and low velocity rocks in upper mantle and calc-Alkaline magmatism of Bhandara craton suggest N-S directed compression and subduction across central part of SFB during Mesoproterozoic period related to Sausar orogeny. Opposite dipping reflectors associated with low density and low conductivity over the Central Indian Shear (CIS) along southern margin of the SFB with different densities and conductivities of rocks on either side of it suggest to it to be a suture. Based on gravity anomalies, extension of the CIS and two phases of granulite rocks related to pre and post Sausar orogeny (1 6 and 1 0 Ga) in central part of the SFB are traced towards east associated with Singhbhum orogeny and towards west upto west coast of India separating Bundelkhand Craton towards north and Dharwar-Bhandara-Singhbhum Cratons towards south. The contemporary Vindhyan Basin of Mesoproterozoic period along the ADFB and the SFB with shelf type of sediments may represent a peripheral foreland basin. There is also a case of extension and compression across the ADFB and the SFB during Paleoproterozoic period related to Aravalli and Mahakoschal orogeny, respectively. This suggest cyclic E-W and N-S directed compression across the ADFB and the SFB, respectively during Paleo and Meso-Proterozoic periods. The gravity highs related to them join together in NW India to form an arcute shaped collision zone indicating resultant stress in NE-SW direction, during these periods. Such cyclic orogeny has been reported from several places in the world such as Appalachan-Caledonian system and in case of several other natural processes.

Seismic section across Dharwar craton provide domal and bowl shaped reflectors in crust under the WDC and the EDC and east ward dipping reflectors below Moho under the EGFB, which suggest extension and compression, respectively supported by paired gravity anomalies. Schist belts of the WDC and the EDC containing riftogenic volcano sedimentary sequences with bimodal volcanics of Neoarchean (3 0-2 7 Ga) and Paleoproterozoic (2 6-2 5 Ga) periods, respectively also suggest extension across the WDC and the EDC during these periods. Regional gravity lows of schist belts of WDC suggest low density crustal rocks under them indicating a marginal or intra arc basin set up for them in plate tectonics paradigm with vertical stretch and transpressive zones to form ischolar_mains due to horizontal flow instead of orogenic belts. Similarly, westward verging thrusts and thrusted high density and high velocity lower crustal rocks under the SZ between the WDC and the EDC and along the EGFB (1 1 Ga) and K-Granite plutons of EDC of 2 6-2 5 Ga suggest west to east directed compression and subduction across SZ and EGFB during these periods. Further south, multi-Disciplinary geophysical investigations along a geotransect across the SGT and modelling of gravity field provide linear gravity highs over the TZ and the CSZ being related to high density intrusives of mafic lower crustal rocks supported from high seismic velocity and high conductivity and adjoining gravity lows towards south of them, are caused by crustal thickening upto 45-46 km. These observations along with opposite dipping thrusts, the MBSZ and the PCSZ and exposed lower crustal rocks of metamorphic ages 2 6-2 5 Ga north of the MBSZ and in the CSZ indicate NS directed compression during this period with the CSZ as central core complex of collision tectonics. Airborne magnetic anomalies indicate that the MBSZ and the PCSZ are connected to NE-SW oriented Mettur shear and Gangavalli shear in the SGT, respectively in their eastern parts extending to east coast of India, forming an arcuate shaped collision zone during 2 6-2 5 Ga. This compressional phase across SGT may be related to contemporary compression across Dharwar Craton towards north with collision between the WDC, the EDC and the SGT during 2 6-2 5 Ga in NW-SE direction with W-E component between the WDC and the EDC and N-S component between Dharwar Craton and the SGT.

Keywords

Crustal Structure, Peninsular Shield, Geophysical Data, Tectonics, Evolution, India.

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D. C. Mishra ¹

Affiliations
1 National Geophysical Research Institute (CSIR), Hyderabad - 500 007, IN

Abstract

Most of the Proterozoic basins in India, viz. the Vindhyan, the Cuddapah and the Pakhal Basins have experienced long hiatus between the upper and the lower group of rocks. It is proposed that the older group of rocks of Paleoproterozoic period (∼1.9-1.6 Ga) formed during the rifting phase caused by large scale magmatism in respective basins possibly due to plume tectonics. On the other hand, the younger group of rocks of Neoproterozoic (∼1.0-0.7 Ga) are formed during the final phase of convergence after mountain building that supplied sediments. These geological processes explain large scale disturbances in the older group of rocks during subsequent convergence and collision as they usually occurred along the rifted margins of the cratons. These processes also explain the undisturbed nature, devoid of magmatic rocks of the younger group of rocks and hiatus of about 0.5-0.6 Ga in each case. It is suggested that the plume that was responsible for these rifting of the Indian cratons during Paleo-Mesoproterozoic might have also been responsible for the break up of contemporary Columbian agglomeration in this section. Same model can be used to explain the formation of Proterozoic basins and related hiatus any where else where similar geological environment exist.

Keywords

Proterozoic Basins, Mobile Belts, Rifting, Convergence and Plate Tectonics.

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