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

A. K. Jain ¹

Affiliations
1 Wadia Institute of Himalayan Geology, University of Delhi, Delhi, IN

Abstract

The metamorphosed basic rocks, probably emplaced along dislocation zones during overthrusting and facilitating such movements, are persistent at the base of Uttarkashi thrust sheet in the Precambrian-Lower Palaeozoic rocks of innermost Lesser Himalayan region of Uttarkashi, Garhwal. Marked absence of such basic rocks in Tertiary rocks, and along thrusts of Sub-Himalaya and outermost Lesser Himalaya in Garhwal, may be taken as indicating a probable Upper Cretaceous age for these intrusives related to the initial phase of Himalayan orogeny.

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V. C. Thakur ¹, A. K. Jain ¹

Affiliations
1 Wadia Institute of Himalayan Geology, Delhi University Campus, Delhi, IN

Abstract

The deformed shapes of pebbles indicate that both the limbs of the Pangin Synform have suffered flattening-type deformation - the normal limb has undergone greater magnitude of flattening than the inverted limb. The longest axes of the pebbles, representing maximum elongation direction Of the tectonic strain ellipsoid, lie parallel and subparallel to the axial direction of the fold.

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A. K. Jain ¹, V. C. Thakur ²

Affiliations
1 Department of Geology and Geophysics, University of Roorkee, Roorkee 247672, U.P, IN
2 Wadia Institute of Himalayan Geology, Dehra Dun, U.P., IN

Abstract

The Abor Volcanics of the Arunachal Himalaya are typically exposed along the Dihang Valley as penecontemporaneous lava flows, sills, dykes, volcanic breccia and metatuffs.

Although the Abor Volcanics are so far considered contemporaneous to the Panjal Volcanics of the North-West Himalaya, they are typically associated with probable Precambrian-Middle Palaeozoic Siang and Mid Groups and are distinctly older to the Gondwana. Thus, Late Precambrian-Lower Palaeozoic volcanic activity is widely manifested in the Himalaya from Kashmir to Arunachal Pradesh and is represented by the Baifliaz Volcanics in Kashmir, Mandt-Darla Volcanics (in parts) in Himachal Pradesh, penecontemporaneous lavas in Garhwal Group in Kumaon and Garhwal, Karnaprayag Volcanics, Bhowali Volcanics and Abor Volcanics. This volcanism is older to an equally widespread Late Palaeozoic volcanism of the Kashmir Himalaya and Eastern Himalaya.

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A. K. Jain ¹

Affiliations
1 Department of Earth Sciences, University of Roorkee, Roorkee 247667 (U.P.), IN

Abstract

Lineament and fracture trace analyses of the Indo-Gangetic Plain and different tectonic units of the Garhwal Himalaya reveal four important sets with strike-slip sense of movements. Horizontally-displaced lithologic and tectonic boundaries clearly depict the sense of displacement along certain lineaments, e.g. the Ganga and Yamuna. Also, small-scale straight fracture traces generally are associated with major fracture traces of lineaments in the sense of Riedel (R), Conjugate Riedel (R'). Displacement (D) and Thrust shears (P). L₁ lineaments trend N5°-N10° and show dextral sense of displacement, while its conjugate sinistral set (L₃) trends N50°. The other strike-slip fracture traces and lineaments trend N25° (L₁) and N90° (L₃) with a dextral and sinistral sense of displacement respectively. Kinematically. it seems that the orientation of maximum principal horizontal stressU 1. deduced from lineament and fracture trace analysis, has changed anticlockwise from N60° to N24° in space and time by an amount of 35°. Interplay of some important faults along some lineaments with the Krol Thrust in frontal parts of the Krol Thrust Sheet has produced the Dehradun Re-entrant as a lateral ramp unlike the other re-entrants in the Himalaya. Furthermore, present-day seismicity in the Garhwal Himalaya is controlled by certain transverse lineaments besides being associated with major thrusts.

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Sandeep Singh ¹, A. K. Jain ¹

Affiliations
1 Department of Earth Sciences, University of Roorkee, Roorkee - 247 667, IN

Abstract

A newly identified Chor Thrust demarcates the southern margin of the Proterozoic Chor granitoid massif within the Jutogh Group metamorphics of the Lesser Himalaya in Himachal Pradesh. Numerous shear criteria reveal a topto- SW overthrust-type Intense ductile strain along this margin and are consistent with the southward propagating nappes.

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Ashok Kumar ¹, Nand Lal ², A. K. Jain ³, R. B. Sorkhabi ⁴

Affiliations
1 Department of Physics, Kurushetra University, Kurukshetra - 132 119, IN
2 Department of Geophysics, Kurukshetrauniversity, Kurukshetra - 132 119, IN
3 Department of Earth Sciences, University of Roorkee, Roorkee - 247 667, IN
4 Department of Geology, ArizonaState University, Tempe, Arizona 85287-1404, US

Abstract

Fission Track (m) ages of apatite and zircon from the Higher Himalayan Crystalline (HHC), SE - Jammu and Kashmiralong Chenab-Suru-Dodarivers and their tributaries provide constraints on the cooling (<250°C) and exhumation history of these rocks. FT ages of apatite/zircon versus the topographic elevations of the host samples from different traverses provide linear relationships, indicating differential and secular nature of exhumation in the Himalaya. The HHC belt is exhumedat a rate of about 0.27 mm/a during Middle to Late Miocene. However, regional exhumation rate near the base along the Main Central Thrust and in central parts of the HHC from FT apatite ages is faster upto 0.35 mm/a since Late Miocene. Exhumation has considerably slowed down to 0.11 mm/a along its northern boundary and 0.02 mm/a along the Zanskar Shear Zone. No apparent faster exhurnationis discernible either along thee MCT or the Zanskar ShearZone (ZSZ). On the other hand, three large fold structures namely the Suru Dome, the Chisoti Dome and the Kishtwaranti formal window have indicated very young and fast exhumation of 0.33 mm/a, 1.1 mm/a and 3.6 mm/a respectively during the last 1 to 5 Ma.

Keywords

Fission Track Ages, Geochronology, Crystallines, NW Himalaya.

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A. K. Jain ¹

Affiliations
1 Department of Earth Sciences, University of Roorkee, Roorkee 247 667, IN

Abstract

No Abstract.

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Bijai Prasad ¹, A. K. Jain ¹

Affiliations
1 KDM Institute of Petroleum Exploration, Oil & Natural Gas Commission, Dehradun-248 195, IN

Abstract

Triassic palynomorph assemblages are recorded from the subsurface sediments of the Krishna-Godavari Basin. Four palynological assemblage zones, ranging in age from Smithian to Norian are identified in different well sections. These assemblages closely resemble Early to Late Triassic palynoflora of northwestern Australia and represent the Onslow type palynoflora.

It is suggested that the subsurface sedimentary sections in this basin, which have yielded typical Smithian to Norian palynoflora, and are termed as "Chintalapudi Sandstones", be referred to as Maleri sequence or its equivalents.

Keywords

Krishna-Godavari Basin, Stratigraphy, Palaeobotany.

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Sandeep Singh ¹, Biswajayee A. Patra ¹, A. R. Vijan ², A. K. Jain ³

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee - 247 667, IN
2 Geochronology Division, KDMIPE, ONGC, Kaulagarh Road, Dehradun - 248 001, IN
3 Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee - 247 667

Abstract

Biotite and K-feldspar Rb-Sr ages from three granitoid intrusives within the Karakoram Metamorphic Belt (KMB), eastern Ladakh yield indistinguishable ages between 12-10 Ma. Since the closure temperature of biotite for Sr diffusion is 300±50°C, we interpret these ages due to exhumation at 10 to 7 km depth within the crust. This implies that the Pangong Metamorphic Belt of the KMB, located at the southern termination of the Eurasian Plate, was undergoing a fast exhumation in a transpressional regime during Middle Miocene. These data also indicates that the southern edge of the Eurasian Plate has exhumed rapidly in comparison to the Higher Himalayan Crystallines within the Indian Plate segment.

Keywords

Rb-Sr Ages, Granitoids, Karakoram Complex, Eastern Ladakh.

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Sandeep Singh ¹, Stefan Claesson ², A. K. Jain ¹, David G. Gee ³, P. G. Andreasson ⁴, R. M. Manickavasagam ⁵

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee - 247 667, IN
2 Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50007, SE- 104 05 Stockholm, SE
3 Department of Earth Sciences, Uppsala University, Villavagen 16, SE-752 36, Uppsala, SE
4 Department of Lithosphere and Biosphere Science, Solvegatan 12, SE-223 62, Lund, SE
5 Institute Instrumentation Centre, Indian Institute of Technology Roorkee, Roorkee 247 667, IN

Abstract

Along the Sutlej valley, the lower package of the Higher Himalayan Crystallines (HHC) exposes a small concordant to discordant intrusive grey granite -The Maglad Khad Granite, within garnet mica schist/Banded gneiss of the Jeori Formation. This body is fine grained and foliated along the margins, whereas the central part is relatively undeformed. This body along with aplites and pegmatites intrudes the country rock during early to syn-D₁ deformation. This is later affected by the most pervasive D₂-deformation producing gneissosity within the granite. U-Pb dating of zircons by conventional isotopic dilution technique yield an upper intercept age of 2068±5 Ma (2σ) from 6 zircon-Fractions with MSWD=0.93, constraining the age of crystallization in the basal parts of the HHC during Early Proterozoic as well as the constraining pre-Himalayan fabric development.

Keywords

Higher Himalayan Crystallines, Maglad Khad Granite, Geochronology, U-Pb Zircon Dating, Sutlej Valley, Himachal Pradesh.

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Priyom Roy ¹, A. K. Jain ², Sandeep Singh ²

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee - 247 667, IN
2 Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee – 247 667, IN

Abstract

The Karakoram Shear Zone is a northwest-southeast trending dextral ductile shear zone, which has affected the granitic and granodioritic bodies of the southern Asian Plate margin in three distinct episodes. The ductile shearing of the granitic bodies at Tangste and Darbuk has resulted in the development of mylonites with mylonitic foliation and stretching lineation. More intense deformation is noted in the Tangste granite grading up to orthomylonite, as compared to the Darbuk granite. Kinematic indicators include S-C foliation, synthetic C' and C" antithetic shear bands, Type A s-mantled porphyroclasts, oblique quartz foliation, micro-shears with bookshelf gliding, mineral fishes including Group 2 mica fishes, and Type 1 and 2a pull-apart microstructures, and exhibit strong dextral sense of ductile shearing towards southeast. The textural features of the minerals, especially that of quartz and feldspar, indicate temperature of mylonitisation ranging between 300 and 500°C in the upper greenschist facies, and appear to have been evolved during exhumation as a consequence of oblique strike-slip movements along the Karakoram shear zone.

Keywords

Karakoram Shear Zone, Mylonites, Texture, Kinematic Indicators, Karakoram, Uttarakhand.

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A. K. Choudhary ¹, A. K. Jain ², Sandeep Singh ², R. M. Manickavasagam ¹, K. Chandra ¹

Affiliations
1 Institute Instrumentation Centre, Indian Institute of Technology Roorkee, Roorkee - 247 667, IN
2 Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee - 247 667, IN

Abstract

This work provides unequivocal evidence of the existence of Mesoarchean granulite facies metamorphic event in the Palghat-Cauvery Shear Zone (PCSZ) of South India. Charnockite samples from two prominent hills at Kollaimalai (KM) and Pachchaimalai (PM) as well as from two quarries within the Bhavani Shear Zone (BSZ) have been analyzed for their Sm-Nd and Rb-Sr ages to investigate the existence or otherwise of the Archean granulite facies events within the PCSZ. The Rb-Sr whole-rock isochron ages for massive charnockites from both the hills appear to be contemporaneous at 2.9 Ga with the initial Sr isotopic ratios of 0.7012 and 0.7014, respectively. However, the Rb-Sr data for whole-rock samples of basic granulites from one of the quarries within the BSZ indicate open system behavior, while the charnockites from the other quarry have insufficient spread in ⁸⁷Rb/⁸⁶Sr ratios and do not yield any isochron. The Sm-Nd data, on the other hand, do not distinguish between the massive charnockite and the lowland charnockite and yield Depleted Mantle model ages in the range 2.98±0.3 Ga for all of them. The ε^T _CHUR for all of these rocks are highly positive. Both the Sr isotopic ratios and positive ε^T _CHUR values for these rocks strongly suggest a mantle source for all of them. An upper age limit of ∼3.28 Ga may be assigned to the crustal accretion of the protolith of all these rocks on the basis of their Nd model ages. The Rb-Sr isochron ages of 2.9 Ga for the two massifs could be the age of granulite facies metamorphism. Thus, the metamorphism in the KM and PM Hills took place within ∼100 Ma of crustal accretion of these rocks and probably was part of the same geological event of crust formation and metamorphism. The open system behavior with respect to Rb-Sr isotopes in the basic granulite from Bhavani is possibly due to the migration of Sr isotopes, triggered during the later shearing of these rocks.

Keywords

Rb-Sr and Sm-Nd Geochronology, Granulite Facies Metamorphism, Southern Granulite Terrain.

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