Browsing by Author "Hari B. Srivastava"

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Age and geochemistry of the paleoproterozoic bhatwari gneiss of garhwal lesser himalaya, nw india: Implications for the pre-himalayan magmatic history of the lesser himalayan basement rocks
(Geological Society of London, 2019) Aranya Sen; Koushik Sen; Hari B. Srivastava; Saurabh Singhal; Purbajyoti Phukon
The Bhatwari Gneiss of Bhagirathi Valley in the Garhwal Himalaya is a Paleoproterozoic crystalline rock from the Inner Lesser Himalayan Sequence. On the basis of field and petrographic analyses, we have classified the Bhatwari Gneiss into two parts: the Lower Bhatwari Gneiss (LBG) and the Upper Bhatwari Gneiss (UBG). The geochemical signatures of these rocks suggest a monzonitic protolith for the LBG and a granitic protolith for the UBG. The UBG has a calc-alkaline S-type granitoid protolith, whereas the LBG has an alkaline I-type granitoid protolith; the UBG is more fractionated. The trace element concentrations suggest a volcanic arc setting for the LBG and a within-plate setting for the UBG. The U–Pb geochronology of one sample from the LBG gives an upper intercept age of 1988 ± 12 Ma (n = 10, MSWD = 2.5). One sample from the UBG gives an upper intercept age of 1895 ± 22 Ma (n = 15, MSWD = 0.82), whereas another sample does not give any upper intercept age, but indicates magmatism from c. 1940 to 1840 Ma. Based on these ages, we infer that the Bhatwari Gneiss has evolved due to arc magmatism and related back-arc rifting over a time period of c. 100 Ma during the Proterozoic. This arc magmatism is related to the formation of the Columbia supercontinent. © 2019 The Author(s). Published by The Geological Society of London. All rights reserved.
Characterizing anatexis in the Greater Himalayan Sequence (Kumaun, NW India) in terms of pressure, temperature, time and deformation
(Elsevier B.V., 2019) Purbajyoti Phukon; Koushik Sen; Praveen Chandra Singh; Aranya Sen; Hari B. Srivastava; Saurabh Singhal
We applied field observations combined with P-T pseudosection modelling, zircon U-Pb geochronology and bulk rock geochemistry along the Kali River Valley, Kumaun Himalaya to understand conditions of peak metamorphism and partial melting of the Greater Himalayan Sequence (GHS) along with spatiotemporal relationship between anatexis and fault activation. The southern tectonic boundary of GHS or the Main Central Thrust (MCT) is marked on the basis of structural, metamorphic and chronological evidences. Outcrop-scale observations suggest generation of partial melt at the base of the MCT. This partial melt migrated to higher structural levels and finally emplaced as tourmaline bearing leucogranite in the northern tectonic boundary of the GHS, which is marked by the South Tibetan Detachment Zone (STDZ). P-T pseudosection modelling shows that GHS have experienced muscovite dehydration melting at 9.2–9.8 kbar and 720°–725 °C, 8.4–8.7 kbar and 700°-710 °C, 7.8–8.4 kbar and 700–720 °C respectively at its lower, lower-middle and middle structural levels. Zircon U-Pb geochronology suggests that the GHS underwent suprasolidus peak metamorphism and post-peak anatexis during a time span of ~26–22 Ma at the base of the MCT and ~32–27 Ma at the middle structural level. The MCT is at least ~22 Ma old, being synkinematic to the partial melting event that took place at its base. Diachronous and brief episodes of partial melting and absence of sillimanite zone at the base of the GHS help us envisage a ‘critical taper wedge’ scenario, where partial melt weakened the overlying Himalayan wedge and triggered gravity collapse that formed the STDZ. © 2019 Elsevier B.V.
Chemical mass transport during deformation and metamorphism: Insights from the Main Central Thrust and its footwall of Western Arunachal Himalaya, NE India
(Elsevier B.V., 2022) Pranjit Kalita; Purbajyoti Phukon; Tapos K. Goswami; Takeshi Imayama; Hari B. Srivastava
The Main Central Thrust (MCT) is one of the major tectonic discontinuities stretching about ~2500 km along the length of the Himalaya and it plays important role during the tectono-metamorphic evolution of Himalayan orogen. This contribution aims to find out the element mobility and loss or gain of chemical mass during mylonitization and migmatization of rocks and their relation with deformation and metamorphism within the Main Central Thrust Zone (MCTz) and its immediate footwall along the Bomdila-Dirang-Seppar section of the Western Arunachal Himalaya, India. Based on meso- and microstructural observations, we divided the Dirang Formation in the footwall of the MCT into 3 units: Lower Mylonite Zone (LMZ), Protomylonite Zone (PMZ) and Upper Mylonite Zone (UMZ), with increasing structural distance from Dirang thrust towards NW. Deformation of the Dirang Formation results in enrichment of Na, K and Si with significant gain in mass of ~55% in the UMZ relative to the PMZ. We inferred that shear strain localization during mylonitization in the UMZ induces textural transitions causing chemical alterations at peak metamorphism conditions of 0.62–0.66 GPa and 690°-710 °C. Migmatites of Lower Structural Position (LSP) show enrichment of Si, Na, K, Ca, Mn and P with depletion of Mg and Fe in the leucosome + mafic selvage (LM) relative to the paleosome with ~13% chemical mass gain. On the other hand, migmatites of Upper Structural Position (USP) are characterized by enrichment of Si, Mn and K and depletion of Ca, Mg, Na, P and Fe in the LM relative to the paleosome with ~17% chemical mass gain. Such chemical changes occur during near peak metamorphic conditions of 0.52–0.63 GPa and 680°-720 °C and it is accompanied by the appearance of sillimanite. This study improves our understanding of the chemical modification of rocks in the MCT and its footwall, which were subjected to deformation and metamorphism during its evolution in Himalayan orogen. The emplacement of the GHS along the MCT buried the Dirang Formation to a depth of ~23–25 km. Interaction of fluids, derived from dewatering of the underthrusted Dirang Formation, induced chemical alteration in the UMZ. We interpret that chemical mass transfer in migmatite zones directly influences the metamorphic reactions that occur during deformation and crustal anatexis in intracontinental shear zones, such as the MCT. © 2022 Elsevier B.V.
Deformation temperature, differential stress, and strain rate variation across the Bomdila Gneiss, western Arunachal Himalaya, India
(Springer Science and Business Media Deutschland GmbH, 2022) Pranjit Kalita; Tapos Kr. Goswami; Purbajyoti Phukon; Hari B. Srivastava
Constraining deformation temperature, differential stress, and strain rate variation from deformed rocks is crucial in developing tectonic models. The outcrop to grain scale fabrics of the Bomdila Gneiss (BG) in the Lesser Himalayan Sequence (LHS) of the western Arunachal Himalaya is studied to understand the variation of the intensity of deformation across the mylonitic batholithic intrusive. The BG represents a Paleoproterozoic magmatic activity in the LHS and subsequently underwent Miocene Himalayan orogenesis. The upper and lower contacts of the BG with Dirang Formation and Miri Quartzite are demarcated by Dirang Thrust (DT) and Bome thrust (BT), respectively, while in the middle, it has another thrust contact with the Tenga Formation, known as the Tenga Thrust (TT). The intensity of deformation across the BG is constrained through microstructural analysis, piezometric study, and fractal dimension analysis. Manifestations of the dynamic recrystallization are evidenced through grain boundary migration, sub-grain rotation, and grain boundary bulging microstructures of quartz crystals. We have estimated the deformation temperatures from microstructural characterization such as grain boundary migration, sub-grain rotation, and grain boundary bulging. The differential flow stresses are calculated through piezometric study. While, the fractal dimension values calculated through area–perimeter method along with deformation temperatures reveal the rates of strain in the BG. The deformation temperatures, differential flow stresses, and rates of strain in the BG are elevated near the thrust zones with maximum near TT and within the BG increases from SE to NW direction towards DT. Both BT and TT are imbrications indicating southward propagation of the thrusts in sequence. The initially buried BG under the Greater Himalayan Crystalline has been considered to exhume through the TT along with BT. An inverted thermal profile within the BG is found along the traverse, which may be due to the thrust imbrications in the MCT footwall. © 2021, Geologische Vereinigung e.V. (GV).
Establishing primary surface rupture evidence and magnitude of the 1697 CE Sadiya earthquake at the Eastern Himalayan Frontal thrust, India
(Nature Research, 2021) Arjun Pandey; R. Jayangondaperumal; György Hetényi; Rao Singh Priyanka; Ishwar Singh; Pradeep Srivastava; Hari B. Srivastava
Historical archives refer to often recurring earthquakes along the Eastern Himalaya for which geological evidence is lacking, raising the question of whether these events ruptured the surface or remained blind, and how do they contribute to the seismic budget of the region, which is home to millions of inhabitants. We report a first mega trench excavation at Himebasti village, Arunachal Pradesh, India, and analyze it with modern geological techniques. The study includes twenty-one radiocarbon dates to limit the timing of displacement after 1445 CE, suggesting that the area was devastated in the 1697 CE event, known as Sadiya Earthquake, with a dip-slip displacement of 15.3 ± 4.6 m. Intensity prediction equations and scaling laws for earthquake rupture size allow us to constraints a magnitude of Mw 7.7–8.1 and a minimum rupture length of ~ 100 km for the 1697 CE earthquake. © 2021, The Author(s).
Estimation of Paleo-ice Sheet Thickness and Evolution of Landforms in Schirmacher Oasis and Adjoining Area, cDML, East Antarctica
(Geological Society of India, 2019) Prakash K. Shrivastava; Sandip K. Roy; Hari B. Srivastava; Amit Dharwadkar
Quaternary period has witnessed perceptible climatic change in Schirmacher region, central Dronning Maud Land (cDML), East Antarctica. There were buildup of ice sheet and its recession throughout the period. The Schirmacher Oasis, Baalsrudfjellet, Veteheia and Veten nunataks are the prominent northernmost exposures in cDML area and play a major role in controlling the ice flow in this region resulting in glacial erosional as well as depositional landforms. These developments reveal vital information about the evolution of the region in Quaternary period. Erosional features such as roche-moutonees, glacially polished and abraded rocky outcrops with excellent preservation of glacial striations indicates the paleo-movement of overriding glaciers. Striations are generally preserved on polished surfaces of bedrock exposed on the high lands, however, glacial striations are also preserved over some mafic and resistant hard rocks in low lying areas. In general, the glacial striations indicate north-northeast movement of paleo ice sheet. Majority of the boulders in east-central valley show their longer axis trending in NNE-WSW to NE-SW directions. The cross cutting relation of striations give the changing directions of paleo ice sheet movement. Further, back calculation of depth of indentation and corresponding ice load gives a value of 100 to 500 m thick paleo-ice sheet in different parts of this region, documenting vast deglaciation in this region. © 2019, GEOL. SOC. INDIA.
Evaluation of a regional strain gradient in mylonitic quartzites from the footwall of the Main Central Thrust Zone (Garhwal Himalaya, India): Inferences from finite strain and AMS analyses
(2009) Nihar R. Tripathy; Hari B. Srivastava; Manish A. Mamtani
The footwall of the Main Central Thrust (MCT) Zone along the Bhagirathi valley comprises a wide zone of mylonitic quartzite and deep-level tectonites. The systematic variation of finite strain parameters (Es, k and v) in the mylonites indicates heterogeneous deformation, which is determined to vary between, simple shear and non-coaxial flattening type. In such a strain regime the outer boundary of the quartz clasts are no longer preserved thus leading to an error in finite strain measurement. In order to supplement the finite strain studies, Anisotropy of Magnetic Susceptibility (AMS) analyses were carried out on the mylonitic quartzites. A systematic variation in degree of anisotropy (P′) with distance from the MCT is documented and is interpreted to be tectonic in origin. Based on these results it is concluded that P′ can be used as a strain-intensity gauge at least on an outcrop scale, where a systematic variation in P′ values from one part of the outcrop to the other can be established. However, the quantitative relation between principal axes of finite strain ellipsoid and AMS axes, magnitude of principal susceptibility difference (ΔK1 and ΔK3) and finite strain magnitude (ε1=ln 1 + e1 and ε3=ln 1 + e3) were related by a logarithmic relationship with a correlation coefficient of 0.844. © 2008 Elsevier Ltd. All rights reserved.
Exhumation mechanisms of the Himalayan metamorphic core in the Bhagirathi Valley, NW India: Insights from an integrated structural and metamorphic analysis
(Elsevier Ltd, 2024) Aranya Sen; Purbajyoti Phukon; Koushik Sen; Subham Bose; Hari B. Srivastava
The Himalayan metamorphic core in the Bhagirathi valley (NW India) consists of low-grade rocks belonging to the Lesser Himalayan Sequence to the south, and of high-grade rocks of the Greater Himalayan Sequence (GHS), to the north. The contact between these two units is a 2–3 km thick high-strain zone known as the Main Central Thrust zone (MCTz). Structural studies in the GHS identify the superposition of foliation (S2) related to tight isoclinal fold (F2) on a pre-existing foliation (S1). S2 was further overprinted by D3 crenulations, and a set of conjugate fractures (D4) overprinted these ductile fabrics. Deformation in the GHS was characterized by top-to-the-SW shearing, which, in its upper structural level, was overprinted by top-to-the-NE extensional shear. Metamorphic analysis shows a moderate T/high P inverted metamorphic sequence with pre-to syn-kinematic, inclusion-rich garnet in the structurally lower part of the GHS and high T-moderate P prograde metamorphism with post-tectonic inclusion-free garnet and evidence of partial melting, in its upper structural level. We envisage that the uppermost part of the GHS and the lower part of the GHS, including the MCTz, are two distinct tectonic slices, separated by a tectono-metamorphic discontinuity. © 2023 Elsevier Ltd
Finite strain and deformation from a refolded region of the Dudatoli-Almora Crystalline, Kumaun Lesser Himalaya
(Elsevier Ltd, 2004) Hari B. Srivastava
The outcrop of the southern extension of Dudatoli Almora-Crystalline Group around Tamadhun in the Kumaun Lesser Himalaya exhibits a map-scale refolded structure. The major lithological units are phyllites, schists and gneisses. The gneisses exhibit deformed feldspar porphyroblasts on mesoscopic and microscopic scales. Deformed feldspar porphyroblasts, were used under the microscope to estimate finite strain in the rocks. Different analytical methods have been compared, of which the Rf/φ method is found to be reliable and sensitive to minor changes in strain pattern. The rocks of the area have undergone three phases of deformation D1, D2 and D3, synchronous to three phases of folding F1, F2 and F3. The early isoclinal folds (F1) of similar type (class 2), appear to have developed by a buckling process. The second (F2) open concentric (class 1B type) folds developed on the limbs of the F1 folds. The presence of rotated feldspar grains and S-C structures on the limbs of F2 folds reveals a flexural-slip mechanism for their development. F3 chevron folds are restricted to the phyllites of the area. The deformation of feldspar grains in the gneisses involves modification of the fabric from low strain (Es=0.34) to high strain (Es=1.10). The strain variations can be related to the general fold geometry and suggest a competency contrast between the matrix and feldspar grains which increase with increased strain intensity and magnitude. This study reveals that the present day strain pattern in the gneissic rocks originated by flexural-slip mechanisms, which took place during the second phase of folding and modified the strain patterns developed during earlier isoclinal folding. © 2004 Elsevier Ltd. All rights reserved.
Fluid assisted rejuvenation of precursor brittle fractures as the habitats of ductile shear zones: An example from the ~2.6 Ga Bundelkhand Granitoid of north-central India
(Elsevier Ltd, 2020) Goutam Sarkar; Sayandeep Banerjee; Sayan Maity; Hari B. Srivastava
Ductile shear zones frequently nucleate on precursor fractures, and usually imitate their initial geometries. The fractures may either predate the ductile shearing episode or form at an early stage of the ductile shearing. In either case, fluids play a pivotal role in the transformation from brittle to ductile mechanisms. However, the exact mechanism(s) triggering the transition from brittle fracturing to ductile shearing remains elusive. The granitoid rocks of the Bundelkhand Craton preserve evidences of at least five growth stages of ductile shear zone, nucleated on precursor fractures. Field and microstructural investigations suggest that these ductile shear zones are always associated with epidote (~70–80% epidote + ~30-20% quartz ± ~5% chlorite) veins. Here, we argue that a fluid, now represented by epidote vein, originated from the breakdown of mafic minerals in the host granitoid, essentially percolated in the fractures that promoted cataclasis at first. The finer grain size resulted from cataclasis coupled with the fluid had weakened the host rock along fractures which eventually nucleated the ductile shear zone. Protracted supply of the fluid and syn-kinematic redistribution by the fluid phase widened the shear zone. © 2020 Elsevier Ltd
Fuzzy gamma based geomatic modelling for landslide hazard susceptibility in a part of Tons river valley, northwest Himalaya, India
(2010) Vaibhava Srivastava; Hari B. Srivastava; R.C. Lakhera
Himalaya, being an active orogen, is continuously undergoing tectonic activities that pose threats of land stability on the mountains. A large number of mass movement occurrences have been observed in a part of the Tons river valley area. Remote sensing and geographical information system (GIS) based techniques have been used to derive and analyse various parameters and attributes pertinent to the landslide hazards. The GIS based analysis in the present work, incorporating the fuzzy membership values from the existing landslides, has been used for spatial modelling of the parameter maps including geology, slope amount, slope aspect, weathering, erosion, drainage influence, tectonic influence and landuse/land cover for landslide hazard zonation. The model has been used to spatially classify the study area into zones of very high, high, moderate, low and very low landslide hazard zones. Eighty-five percent of the active landslides have been observed to occur in very high and high hazard zones. © 2010 Taylor & Francis.
Geochemistry of Mesoproterozoic Deonar Pyroclastics from Vindhyan Supergroup of Central India: Evidences of felsic magmatism in the Son valley
(Geological Society of India, 2017) Meenal Mishra; Vaibhava Srivastava; P.K. Sinha; Hari B. Srivastava
Deonar Pyroclastics of Semri Group in the Vindhyan Supergroup originated as a result of violent and explosive intrabasinal submarine volcanism during the Mesoproterozoic period. These pyroclastics are rhyolitic to rhyodacitic in composition, comprised of banded, massive, pumiceous flow, breccia, vitric tuff, lapilli and volcanic bomb. The pyroclastic deposits represent welded and non-welded ignimbrites, exhibit typical eutaxitic texture. Mantle normalized multi-element patterns show enrichment in LILs and depletion in HFSFs. Ti, Nb and REE contents show close correlation with Zr, indicating their immobile character. HFSEs and Th/Nb, La/Nb and Zr/Nb values indicate contamination and these signatures represent mixing between mantle-derived rocks and the average continental crust. Deonar Pyroclastics reflect continental rift environment. Felsic magma plausibly generated by underplating of the mature Proterozoic crust of the Indian craton (which acted like a ‘heating lens’) resulted in extensive melting of metabasalt in the lower crustal levels. The high heat flow beneath the Indian shield accentuated heat generation which led to extensive partial melting of metabasalts. Thus, generation of rhyolitic magma occurred along the reactivated deep seated fractures and rifting of the craton, resulting in the explosive intra-basinal felsic vulcanicity in the Vindhyan basin. © 2017, Geological Society of India.
Geometrical analysis of mesoscopic shear zones in the crystalline rocks of MCT zone of Garhwal Higher Himalaya
(2007) Hari B. Srivastava; Nihar R. Tripathy
The crystalline rocks of the MCT Zone of Garhwal Higher Himalaya exhibit well-preserved mesoscopic shear zones. Majority of these shear zones are of ductile and brittle ductile type with both sinistral and dextral sense of movement. Detailed analysis of mesoscopic shear zones reveals that sinistral shear zones exhibit a strike variation from NNE to ENE and dextral shear zones exhibit variation from NNW to WNW directions thus forming a conjugate pair. The bisectors of statistically preferred orientations of the two sets of the shears indicate that they generated due to NNE-SSW horizontal compression. These dextral and sinistral shear zones exhibit strike-slip geometry developed during progressive ductile shearing. © 2006 Elsevier Ltd. All rights reserved.
Late Quaternary geomorphic evolution of Teesta-Khangtse basin, north Sikkim
(Elsevier B.V., 2022) Prakash K. Shrivastava; Gyaneshwar Singh; Siddhartha J. Thapa; R. Chunchekar; Hari B. Srivastava; Vijay V. Mugal
Quaternary climate change in eastern Himalaya is evidenced by a variety of glacial and fluvial landforms. In eastern Himalaya, the Teesta Khangtse glacier region located in the North District, Sikkim, has preserved many glacial and glacio-fluvial geomorphic features. The Optically stimulated luminescence (OSL) geochronology of lateral, recessional and ground moraines has provided proper evidence of episodic deglaciation and corresponding landform evolution of the region. The field disposition ground moraines exhibit the existence of a vast glacier system before 52 ka and successive different stages of its recession in the Late Quaternary time. The thinning of the glacier system laid down a thick cover of the ground moraine. Data show that the major recession of the Teesta glacier system took place in the Upper Pleistocene at around 52 ± 3 ka. This was followed by many episodic deglaciations between 11.4 and 1.4 ka. The recessional phase, close to the beginning of the Meghalayan stages of Holocene at 3.4 ± 0.2 ka, has been marked by fluvial and aeolian activities. © 2022 Elsevier B.V. and NIPR
Magnetic susceptibility mapping of roadside pollution in the Banaras Hindu University campus, Varanasi, India
(Indian Academy of Sciences, 2021) Sayandeep Banerjee; Ankit Kumar; Virendra Rana; Sayan Maity; Hari B. Srivastava
Among the several methods to determine anthropogenic pollutants in the soil, magnetic susceptibility measurements have proven to be useful for rapid and effective diagnosis of magnetic particles and overall screening of pollution. Magnetic particles and other heavy metals accumulated in the topsoil as a result of roadside pollution, contribute to the bulk magnetic susceptibility (χ ). Thus, χ values of the soil can be utilized as a proxy to delineate the zones of high and low roadside pollution in an area. In this study, magnetic susceptibility measurements of the topsoil have been carried out and a quantitative assessment of roadside pollution in the Banaras Hindu University (BHU) campus, Varanasi, India is presented. Based on the χ values of 212 soil samples covering 1300 acres of the campus, zones of high and low roadside pollution are demarcated. The present study has not only deciphered the spatial variation of pollutants in the BHU campus, but has also characterized the magnetic phases responsible for the susceptibility signal on the roadsides inside the campus. The obtained results are crucial for environmental monitoring and prioritization of land use and other anthropogenic activities inside the BHU campus. The modus operandi adopted here would be beneficial for mapping areas exposed to different levels of pollution intensity, for tracing the pollution transport and can be effectively applied to various ecosystems © 2021. Current Science. All Rights Reserved.
New Magnetic Fabric Data from Almora Crystalline Rocks around Rameshwar, Near North Almora Thrust
(Springer, 2020) Vibha Katiyar; S.K. Patil; Hari B. Srivastava
In this paper, Anisotropy of Magnetic Susceptibility (AMS) data from the rocks of Almora crystalline in the vicinity of Rameshwar is presented. The study integrates field, microstructural and Anisotropy of Magnetic Susceptibility (AMS) studies. Field foliation strike shows NW-SE orientation with moderate to high dip in rocks of Almora Crystalline, whereas near North Almora Thrust rocks of Almora Crystalline are steeply dipping and litho-units are intensely mylonitized due to NE-SW regional compression. The magnetic foliations are recorded to be parallel to the field foliation of the study area. Variation in orientation of magnetic lineation is inferred to imply superposed deformation in the study area. AMS study also reveals that the shape of susceptibility ellipsoid is oblate which is inferred to be due to compression. © 2020, Geological Society of India.
Palaeoproterozoic rift-related alkaline magmatism in Bari area, Son valley, Central India
(Elsevier B.V., 2024) G. Mageswarii; Meenal Mishra; Vaibhava Srivastava; Hari B. Srivastava; M. Satyanarayanan; J.P. Shrivastava
Earlier studies on Palaeoproterozoic (∼1800 Ma) alkaline (shoshonitic) rocks comprised of limited petrochemical data on the Bari syenite and other contiguous felsic rocks emplaced in anorogenic rift setting along the Son-Narmada North Fault (SNNF). Using new major and trace element data-sets, this study offers means of study of origin, source of magma, tectonic settings and geodynamic implications. The major oxide chemistry grouped Bari rocks into high alkali, but low CaO bearing peraluminous alkaline rocks. These rocks represent high abundance of HREE, Zr, Nb, Ga, Y, Eu, Ba and Sr. Primitive mantle normalized REE and trace elemental patterns correspond to A-type suite, suggesting origin of the magma mainly from the mantle. Significantly, anomalous Th/U and Rb/Cs values revealed crustal contamination of the melt, derived from partial melting of the mantle. Moreover, binary data plots between La vs. La/Sm and La vs. La/Yb are pointing towards crustal assimilation which was concomitant with the fractional crystallization of the mantle derived melt. Thus, crustal contamination coupled with the fractional crystallization of the melt mainly contributed to the formation of syenite melt. But, a high degree of partial melting of the lower crust was primarily responsible for the formation of Bari granite. The enrichment of incompatible elements in the syenite rocks suggests involvement of mantle metasomatism in their genesis. The magmatic processes related to the formation of syenite, lamprophyre, ultramafics, mafic and granite bodies were operative in the diverse magmatic realm and initiated earlier at the waning stage of the Mahakoshal orogeny and continental rifting, but magma emplaced later during Post-Mahakoshal orogeny and Pre-Vindhyan sedimentation that also in a rifted basement of the Bundelkhand craton at ∼1800 Ma during the amalgamation of the Columbian Supercontinent. © 2023
Petrology and geochemistry of Proterozoic olivine tholeiite intrusives from the Central crystallines of the western Arunachal Himalaya, india: Evidence for a depleted mantle
(2009) Rajesh K. Srivastava; Hari B. Srivastava; Vaibhava Srivastava
A number of plugs and dykes of mafic rocks are encountered between Se La and Jung areas of the Central Crystalline rocks of western Arunanchal Himalaya. These mafic intrusives are emplaced within the Paleoproterozoic high to medium grade schists and gneisses of Se La Group. These mafic rocks are metamorphosed and composed of hornblende (~70%) and plagioclase showing granoblastic texture. Geochemicallythey show olivine tholeiitic characteristics. Appreciable amount of normative hypersthene and olivine is present in all samples. The geochemistry of high-field strength (+ rare-earth) elements suggests that these mafic rocks are co-genetic and derived from olivine tholeiite melt generated from a depleted lherzolite mantle source. These mafic rocks show very close geochemical similarities with mafic rocks reported from the western Himalaya. The satellite imageries suggest that these mafic intrusive rocks are exposed at intersection of major lineaments. The association of these mafic rocks with major lineaments, mostly fault planes, advocates that these originally deep seated intrusions have been upthrown and exposed along the fault planes.
Retraction notice to "Finite strain and deformation from a refolded region of the Dudatoli-Almora Crystalline, Kumaun Lesser Himalaya" [J. Asian Earth Sci. 24 (2004) 115-125]
(2014) Hari B. Srivastava
[No abstract available]
Role of lithology, weathering and precipitation on water chemistry of lakes from Larsemann Hills and Schirmacher Oasis of East Antarctica
(Editorial Office of Advances in Polar Science, 2019) Rajesh Asthana; Prakash K. Shrivastava; Hari B. Srivastava; Ashit K. Swain; Mirza Javed Beg; Amit Dharwadkar
Schirmacher Oasis and Larsemann Hills areas represent two different periglacial environments of East Antarctica. Schirmacher Oasis is characterized by a vast stretch of ice-shelf in the north and East Antarctic Ice Sheet (EAIS) to its south. Whereas, in Larsemann Hills area the northern and north-western boundary is coastal area and EAIS in the southern part, exhibiting polar lowland between the marine and continental glacial ecosystems. Physico-chemical parameters of water samples from different lakes of both of these two distinct locations are quite contrasting and have indicated influence of lithology, weathering, evaporation and precipitation. The lake water chemistry in Larsemann Hills area is mainly governed by the lithology of the area while Schirmacher lakes exhibit influence of precipitation and rock composition. All major ions of lake waters indicate balanced ionic concentrations. The atmospheric precipitation has significantly modified the ionic distributions in the lakes and channels. Carbonation is the main proton supplying geochemical reactions involved in the rock weathering and this is an important mechanism which controls the hydrochemistry. The lake water hydrochemistry differs widely not only between two distant periglacial zones but also within a short distance of a single periglacial entity, indicating influence of territorial climate over hydrochemistry. © 2019, Editorial Office of Advances in Polar Science. All rights reserved.