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Sharma, Rajesh
- Evolution and Resetting of the Fluids in Manikaran Quartzite, Himachal Pradesh: Application to Burial and Recrystallization
Authors
1 Wadia Institute of Himalayan Geology, Dehra Dun - 248 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 51, No 6 (1998), Pagination: 785-792Abstract
Primary aqueous fluid inclusions trapped in Manikaran Quartzite suggest a depth of burial about 4 to 7 km and entrapment temperature from 67 to 146°C. The later thrust-related recrystallization occurred in H2O-CO2 fluid regime under greenschist facies conditions. This event also resulted in thermal resetting of some aqueous inclusions trapped in original grains.Keywords
Fluid Inclusion, Burial Metamorphism, Himachal Pradesh.
- Geothermobarometry and Fluid Inclusion Studies of Leucogneisses from Schirmacher Region, East Antarctica
Authors
1 Wadia Institute of Himalayan Geology, 33, General Mahadeo Singh Road, Dehradun - 248 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 51, No 5 (1998), Pagination: 595-607Abstract
The granulite-gneiss terrain of Schirmacher region, East Antarctica includes mafic to acid granulites pervasively intruded by stringers, bands, lenses and stocks of felsic rocks. The late stage felsic rocks are the leucocratic rocks and are the focus of this paper. They have concordant to discordant relation with the associated felsic and other granulitic rocks of the region.
The fluid inclusions, show three stages of f1uid entrapment. The monophase CO2 inclusions, with densities in the range of 0.996 to 0.811 g/cm3, show pressures of about 5.1 ± 0.6 kbars at inferred temperatures of 675 ± 25°C and indicate peak metamorphism after crystallization. Early stage deformed aqueous inclusions, however, represent initial crystallization. Entrapment of these inclusions was followed by carbonic aqueous inclusions, whose CO2 densities range from 0.816 to 0.624 g/cm3 with increasing H2O fluid entrapment occurring during the retrogressive stages. The increased concentration of aqueous fluids has resulted in biphase aqueous inclusions in trails. Their density and homogenization temperatures indicate a pressure of 2 ± 0.5 kbars.
The P-T trend observed from fluid inclusion studies is ref1ected from mineral equilibria studies. The GMBPQ assemblage of these rocks gave temperatures and pressures of 675 ± 25°C and 5.5 ± 0.3 kbars respectively. Further, the two-feldspar thermometry for these rocks record a reequilibrated temperatures of 444 ± 9°C. These P-T conditions of the leucogneisses suggest around 18 km of crust to have been removed, indicating > 50 km thick crust during the amphibolite facies metamorphism corresponding to geothermal gradients of around 37°C/km. A successive decrease in estimated P-T conditions along with density and compositional information suggests retrogression and compressional cooling path for these rocks.
Keywords
Geothermobarometry, Fluid Inclusion Studies, Granulite, Antarctica.- Syn-Sedimentary and Later Remobilised Epithermal Pb-Zn Mineralisation of the Great Limestone, Riasi, J & K - Signatures in Fluid Inclusions and Stable Isotope Compositions
Authors
1 Regional Research Laboratory, Bhubaneswar 751013, IN
2 Wadia Institute of Himalayan Geology, Dehra Dun 248001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 38, No 5 (1991), Pagination: 516-523Abstract
A strong stratigraphic control is exhibited by the sporadic Pb-Zn occurrences in the Great Limestone of Riasi, J & K. Fluid inclusion thermometry and stable isotope data suggest their remobilisation and concentration in the fractures developed in the host-rock at the time of orogenic movements and the final deposition may be due to the mingling of at least two fluids; one epithermal; generated due to orogenesis and the other, meteoric water.Keywords
Pb-Zn Mineralization, Great Limestone, Riasi, Jammu and Kashmir, Fluid Inclusion.- Magnesite Mineralisation Along the Chamba Thrust, Himachal Himalaya : Structural Control and Depositional Environment Using Fluid Inclusions
Authors
1 Wadia Institute of Himalayan Geology, 33, General Mahadeo Singh Road, Dehra Dun-248 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 49, No 3 (1997), Pagination: 289-296Abstract
The study reports magnesite mineralisation along the Chamba Thrust. The Tethyan rocks occurring south of the Higher Himalaya have translated along the Chamba-Thrust over the Higher Himalayan Crystallines and the Chail Thrust Sheet. Localized occurrences of magnesite along the Chamba Thrust are from Jiuni of Brahmour and Bindrabani of the Pangi valley areas. The fluid inclusion studies of magnesite and dolomite, indicate that the fluid involved in the genesis of magnesite was hot saline in nature at about 200°C to 275°C. The magnesite is formed from the reaction of this fluid with the limestone/dolomite during thrusting.Keywords
Economic Geology, Magnesite, Fluid Inclusions, Himachal Himalaya.- W-Mineralization in Sewariya Area, South Delhi Fold Belt, Northwestern India: Fluid Inclusion Evidence for Tungsten Transport and Conditions of Ore formation
Authors
1 Wadia Institute of Himalayan Geology, 33, G. M. S. Road, Dehra Dun - 248001, IN
2 Geological Survey of India, Jawaharlal Nehru Marg, Kolkata - 700 016, IN
3 Department of Geology, University of Rajasthan, Jaipur - 302004, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 61, No 1 (2003), Pagination: 37-50Abstract
The S-type, high-level, biotite granite (Sewariya Granite) intruding the metasediments of the South Delhi Fold Belt in central Rajasthan hosts W-mineralization that occurs within the shear controlled late-stage quartz veins. The fluid inclusion data of the observed type 1 to type 4 inclusions in mineralized quartz veins and type 1, type 2 inclusions in fluorite reveal that the high to low temperature alkali chloride solution was in equilibrium with syn to post W-mineralization events. Boiling at a temperature range of 373 to 417°C is recorded in the earliest fluid inclusions viz. gas rich type 2 and liquid rich type 3 inclusions, which together show a continuum in the fluid density from 0,2 to 0.85 g/cm3. Dominance of high saline aqueous fluid with 32.5 to 43.3 equiv. wt percent NaCl is represented in type 1 inclusions. The increase in salinity to the extent of Tm NaCl> Th L-V is attributed to the boiling of fluid and successive influx of high saline hydrothermal fluid exsolved from crystallizing granite source rocks. Type 1 inclusions of fluorite show a difference from type 1 inclusions of mineralized quartz in terms of their lower temperature and a common Th> Tm NaCl homogenization trend. Type 4 inclusions are secondary mostly homogenized below 170°C,these are unrelated to the mineralization event. The observed conditions favour the interpretation that tungsten was transported as tungstic acid in the CI and vapour rich hot hydrothermal solution. A low pressure of 250-350 bars at about 400°C is suggested for this W-mineralization.Keywords
Tungsten Mineralization, Sewariya Granite, Fluid Inclusions, Delhi Fold Belt, Rajasthan.- Petrogenesis of the Granitoid Rocks from Askot Crystallines, Kumaun Himalaya
Authors
1 Wadia Institute of Himalayan Geology, 33 General Mahadeo Singh Road, Dehradun - 248 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 74, No 3 (2009), Pagination: 363-374Abstract
The Askot crystallines form a doubly plunging synformal belt and occurs as a detached crystalline belt or klippen in the vast sedimentary terrain lying between Central crystallines towards north and the Almora crystallines to the south. It is dominated by granite gneiss and augen gneiss, and also comprise of metapelites, migmatites and basic intrusives. In this paper, the geochemical studies of the granite gneiss and augen gneiss from the Askot crystallines, Kumaun Himalaya were carried out in order to understand their origin and evolution.
The granite gneiss is generally foliated, with less foliated and porphyritic variety seen in the core part. The K-feldspar shows Carlsbad twinning, while plagioclases show complex twinning. They show euhedral zircon and apatite along with titanite as accessory minerals. The granite gneiss is moderately evolved (Mg# ~50) and has granodiorite composition with metaluminous, calc-alkaline trends. They show higher concentration of Ti, Ca, Mg and low abundance of ΣREE (~165 ppm) in comparison to augen gneiss. They show volcanic arc signatures and compare well with Lateorogenic granites of Proterozoic times distributed world wide. These calc-alkaline granites appear derived from a Paleoproterozoic mafic/intermediate lower-crust reservoir probably involving arc magma underplating. Granite gneiss is also peraluminous with molar A/CNK>1.1, and the heterogeneity of granite gneiss can be explained with the precursor melts, experiencing assimilation during up-rise through crust or contamination of source itself involving sediments from the subduction zone.
The augen gneiss is more evolved (Mg# ~18) and show granite composition. They show megacrysts of perthites in a fine-to medium-grained matrix of feldspars and micas. The REE pattern of the augen gneiss shows much wide compositional variation (ΣREE ~171 ppm) than granite gneiss. It shows syn- to post-orogenic environment and derivation from the partial melting of an upper crustal source. Existing Rb-Sr isotopic data suggest that the granite gneiss defines an isochron age of ~1700-1800 Ma with a Sri ratio of ~0.71, while the augen gneiss defines an age of ~1300 Ma with much evolved Sri ratio (~1.65). The dominance of granite gneiss in the eastern Kumaun region suggests the production of heterogeneous granitic melts similar to those of Askot crystallines as an important event of crustal growth during Late Paleoproterozoic period in the region.
Keywords
Granites, Augen Gneiss, Petrogenesis, Askot Crystallines, Kumaun Himalaya.References
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- The Role of Fluids in the Formation of Talc Deposits of Rema Area, Kumaun Lesser Himalaya
Authors
1 Wadia Institute of Himalayan Geology, Dehra Dun - 248 001, IN
2 Department of Geology, Kumaun University, Nainital - 253 002, IN