Y. J. Bhaskar Rao

National Geophysical Research Institute | Ngri · Department of Geochemistry and Geochronology

Zircon age-Hf isotopic data on the Archean Singhbhum and Dharwar cratons and the Archean-Proterozoic Southern Granulite Terrain (SGT) obtained at the CSIR-NGRI and by others elsewhere are in focus here. These data are used to decipher episodes of juvenile crust formation in the protracted (collectively spanning ∼3.7 billion years) geologic history...

Changes in the dominant tectonic regimes and the modes of formation and maturation of the continental crust during the Precambrian are a subject of active debate. Here, we discuss these issues in terms of new information on the crustal and lithospheric architecture of the different terranes in the Eastern part of the Indian Shield (EIS). We present...

An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga (billion years). However, the manifestations of this change may have been diachronous and craton-specific. Here, we review geological, geophysical and geochronological data (mainly zircon U-Pb age–Hf isotope compositions) from...

An emerging view is that Earth’s geodynamic regime witnessed a fundamental transition towards plate tectonics around 3.0 Ga (billion years). However, the manifestations of this change may have been diachronous and craton-specific. Here, we review geological, geophysical and geochronological data (mainly zircon U-Pb age–Hf isotope compositions) from...

The dominant geodynamic processes that underpin the formation and evolution of Earth's early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei. Here, we present U–Pb ages and Hf isotopic compositions of detrital zircon grains from ∼2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from t...

Investigation of large scale suture zones in old continental interiors offers insights into the evolution of continents. The Dharwar Craton (DC) and the Southern Granulite Terrain(SGT) of the Indian shield represent large segments of Precambrian middle to lower crust and preserve a geological record spanning from Mesoarchean to Cambrian. This study...

Major part of the Earth's continental crust is evolved during the Archean, however, the mechanism for its formation is controversial. It could have formed either through horizontal accretion similar to the modern plate tectonic processes or by vertical accretion by plume activity. Here, we present the results of a new deep crustal seismic reflectio...

Deep boreholes around the Koyna-Warna seismic zone in the southwestern part of the Deccan Volcanic Province (DVP) enable a rare access to the basement beneath the thick (typically 1-2 km) lava pile, the nature of which has been enigmatic for long. Utilizing the drill core from borehole KBH-1 near Rasati village, we present here in situ Laser Ablati...

The Southern Granulite terrane, southern India, comprises a vast exposure of deep crust and forms a key region in the reconstruction of the Gondwana supercontinent. An E-W-trending crustal-scale shear zone, the Palghat-Cauvery suture zone system, which formed during the late Neoproterozoic-Cambrian (0.75-0.50 Ga), marks a prominent terrane boundary...

During the last quadrennial period, (2012-2016), many aspects of the Precambrian geology of the Indian peninsula were revisited by Indian geoscientists and their collaborators with the advantage of modern analytical techniques for geochronology as well as new perspectives on global geodynamics in space and time. Important contributions were made to...

This study attempts to understand the upper mantle deformation pattern beneath the northern part of Southern Granulite Terrain (SGT), located to the south of Archean Dharwar craton in south India. The study region comprises the tectonic blocks - Nilgiri, Biligiri Rangan, Shevaroy and Madras blocks - separated from the northern part of Madurai block...

The National Geophysical Research Institute, Hyderabad, under the aegis of the Council of Scientific and Industrial Research, New Delhi, continued its scientific pursuit in many important areas of basic and applied earth sciences research encompassing geophysics, geology, geochemistry, geochronology and geodesy during the year 2014. The Institute i...

In the present study, we analyze the strike-slip-type earthquakes along the Himalayan arc that are transverse to the collision front, with a special emphasis on the Sikkim region. The study examines seismicity and focal mechanism data in conjunction with crustal structure derived from receiver functions and gravity gradients, supported by results f...

Artificial water reservoir-triggered earthquakes have continued at Koyna in the Deccan Traps province, India, since the impoundment of the Shivaji Sagar reservoir in 1962. Existing models, to comprehend the genesis of triggered earthquakes, suffer from lack of observations in the near field. To investigate further, scientific deep drilling and sett...

We report here the salient features of the recently concluded International Continental Scientific Drilling Program (ICDP) workshop in Koyna, India. This workshop was a sequel to the earlier held ICDP workshop in Hyderabad and Koyna in 2011. A total of 49 experts (37 from India and 12 from 8 other countries) spent 3 days reviewing the work carried...

The Southern Granulite Terrain (SGT) of southern India comprises a collage of Archean and Neoproterozoic high-grade metamorphic terrains, where the regional tectonic and high-grade metamorphic events culminated at ca. 2.52 Ga in the northern granulite blocks and ca. 0.55 Ga in the Neoproterozoic Madurai and Trivandrum Blocks. These domains were pre...

The National Geophysical Research Institute (NGRI) was established in 1961 under the Council of Scientific and Industrial Research (CSIR), Ministry of Science and Technology, Government of India, recognizing the importance of geophysics and allied disciplines for the country. NGRI made consistent and substantial advancements over a long period of t...

No abstract available. doi:10.2204/iodp.sd.12.07.2011

Workshop on Deep Scientific Drilling to Study Reservoir Triggered Earthquakes; Koyna, India, 21--25 March 2011; The Koyna region in western India is a classical site of reservoir-triggered seismicity in an intraplate setting. Triggered earthquakes have been occurring in a restricted area of 20 × 30 square kilometers since the impoundment of Shivaji...

We report here the salient features of the recently concluded International Continental Scientific Drilling Program (ICDP) workshop in Koyna, India. This workshop was a sequel to the earlier held ICDP workshop in Hyderabad and Koyna in 2011. A total of 49 experts (37 from India and 12 from 8 other countries) spent 3 days reviewing the work carried...

The age of pseudotachylite formation in the crustal-scale Cauvery Shear Zone system of the Precambrian Southern Granulite Terrain (South India) has been analyzed by laser-probe 40Ar–39Ar dating. Laser spot analyses from a pseudotachylite from the Salem–Attur shear zone have yielded ages ranging from 1214 to 904 Ma. Some evidence for the presence of...

Regional structural mapping, guided by remote sensing interpretation, in the eastern part of the Cauvery shear zone (CSZ), southern Granulite Terrain, reveals a structural framework of two major boundary shear zones interlinked by a set of sigmoidal shear belts. The strain pattern and deformational history are manifest in terms of two major episode...

Major, trace element compositions and Sr–Nd isotopic characteristics of charnockitic gneisses from the Southern Granulite Terrain (SGT), South India are presented. The study region encompasses the central segment of the Cauvery Shear Zone system (CSZ) and regions within the Madurai Block (MB) immediately south of it (designated here as the CSZ/MB a...

The Cauvery Shear Zone (CSZ) is a crustal-scale shear system within the Southern Granulite Terrain along the southern margin of the Archaean Dharwar craton. Structural interpretation of satellite data and field observations reveal four major shear zones within the CSZ system. They show dextral shear kinematics synchronous with a major Neoproterozoi...

The paper describes a typical field example of rarely preserved complex structural patterns related to constrictional strain from the deeply eroded central part of the Neoproterozoic crustal-scale Cauvery shear zone system, southern India. The area exposes intense migmatisation and a distinctive map pattern of a broad domal structure with complex s...

The Pangidi Anorthosite Complex (PAC) is a small, magmatically layered body emplaced into high-grade supracrustal rocks and metamorphosed together with the host rocks in the southern sector of the Eastern Ghats Granulite Belt, South India. It is dominated by coarse-grained anorthosite and leuconorite, minor leucogabbronorite and ultramafics with ch...

The chronology of tectonometamorphic events in granulite terranes of Dronning Maud Land, East Antarctica, is relevant to the controversy regarding the correlation of the Neoproterozoic East African Orogen into Antarctica. The Schirmacher Oasis in the northern Dronning Maud Land preserves medium-pressure (8 kbar, 800degreesC) granulite assemblages w...

Two late Cretaceous mafic dykes with an ENE strike that is orthogonal to the west coast of India and located nearly 200 km inland around Huliyardurga, Karnataka state, yield 40Ar-39Ar plateau ages of 90.0±1.0 and 87.5±0.9 Ma. These Fe-Ti-enriched tholeiites are essentially co-eval with at least four other igneous suites widely scattered in southern...

Whole-rock Sm-Nd isochron ages are reported for two stratiform meta-anorthosite complexes emplaced into the Archean supracrustal-gneiss association in the amphibolite facies terrain around Holenarsipur, in the Dharwar craton, South India. While these metaperidotite-pyroxenite-gabbro-anorthosite complexes are petrologically and geochemically similar...

The Pb, Sr and Nd isotopic compositions were determined on uranium mineralised and barren stromatolitic dolomite samples from the Vempalle and Tadpatri Formations of the Cuddapah Supergroup in southern India. Subsamples from individual handspecimens were analyzed to minimize the potential of heterogeneous initial Pb compositions. All of the U-miner...

A rare occurrence of both steep and shallow plunging stretching lineations within a single outcrop, has been described from the Salem-Attur shear belt, and the regional variations in the orientation of stretching lineations are discussed in terms of transpressional tectonics in the Cauvery shear system, southern granulite terrane, South India.

SHRIMP U-Pb analyses of zircons from a rhyolite sample collected from the Daginkatte Formation of the Chitradurga Group (Dharwar Supergroup), close to the type locality, give an age of 2601 ± 6 Ma (1σ 23 of 24 analysed grains). This is within error of the 2614 ± 8 Ma (2σ 11 grains) recently reported by A.P. Nutman and his colleagues in 1996 from a...

Well constrained SmNd arrays of whole rocks are reported for the first time from three important stratigraphic units of the Dharwar volcano-sedimentary sequence of south India. If interpreted as isochrons, these arrays will correspond to the following ages and initial Nd ratios relative to CHUR: 2.911±0.049 Ga and −0.20 ± 0.40 for the Kalasapura m...

 Sittampundi and Bhavani Archean layered meta-anorthosite complexes occur as tectonic lenses within the Cauvery shear zone (CSZ), a crustal scale shear dividing the Precambrian granulite crust of south India into late Archean (> 2.5 Ga) and Proterozoic (c. 0.55 Ga) blocks. They and their host supracrustal-gneiss rocks record at least two stages of...

The middle to late Archaean rocks of Kola and Karelia in the eastern Baltic shield consist of the Infracomplex overlain by the Saamian complex, and the Lopian greenstone belts. The Infracomplex which forms the basement is a polymigmatite, parts of which are at least 3100 Ma old. The Saamian in the central Belomorian region comprises granite gneiss,...

A new terrane of granulite facies rocks-the Karimnagar granulite terrane (KGT) is identified. The KGT is ~ 150 km x 20 km extending along NW-SE in the Karimnagar, Warangal and Khammam districts of Andhra Pradesh along the southern flank of the Godavari graben which separates the Dharwar and Bastar Cratons. The KGT is interesting because of its loca...

The Archean greenstone sequence of the Dharwar craton is intruded by late- and post-kinematic granites like the Chitradurga and Toranagallu (Closepet) granites with whole-rock RbSr isochron ages of 2603 ± 28 Ma (2σ) and 2452 ± 50 Ma, respectively. The whole-rock RbSr ages of their host metavolcanic rocks show a wide variation; Bababudan, 2728 ± 1...

The Peninsular Gneiss around Gorur in the Dharwar craton, reported to be one of the oldest gneisses, shows nealy E-W striking gneissosity parallel to the axial planes of a set of isoclinal folds (DhF1). These have been over printed by near-coaxial open folding (DhF12) and non-coaxial upright folding on almost N-S trend (DhF2). This structural seque...

Palaeomagnetic, geochemical and geochronological studies have been conducted on a set of dolerite dykes intruding the Peninsular gneisses near Huliyurdurga town, Karnataka, as a reconnaissance survey indicated a Cretaceous age for them. The dykes are mainly tholeiitic in composition with their 87Sr/86Sr ratios tightly clustered around 0·7045. Their...