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Sunil Dhar ¹, Robert Frei ², Jan D. Kramers ², Thomas F. Nagler ², Naresh Kochhar ³

Affiliations
1 Post Graduate Department of Geology, Govt College, Dharamsala, Himachal Pradesh - 176 215, IN
2 Isotope Geology Group, Mineralogical-Petrographical Institute, University of Bern, Erlachstr. 9A, CH-3012 Bern, CH
3 Department of Geology, Panjab University, Chandigarh - 160 014, IN

Abstract

The Jalor and Siwana complexes belong to the Malani igneous suite, Rajasthan, India and are characterised by within - plate, A - type granites associated with coeval felsic and mafic volcanism. Sr, Pb and Nd isotopic compostions of the two complexes have been determined. Sr isotopic studies reveal an isochron age of 725±7 Ma for the felsic rocks of the Jalor Complex, with an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7062±0.0020. Three highly differentiated granites from Siwana plot on the same near-isochron, indicating that the complexes are coeval. The Pb and Nd isotopic ratios range between (²⁰⁶Pb/²⁰⁴Pb = 18.52-21.28, ²⁰⁷Pb²⁰⁸Pb = 15.58-15.98, ²⁰⁴Pb/²⁰⁴Pb/²⁰⁶Pb = 38.53-40.8) and (¹⁴³Nd/¹⁴⁴Nd = 0.5122-0.5127, ¹⁴⁷Sm/¹⁴⁴Nd = 1.1260-0.157) respectively. Pb and Nd isotopic compositions of the Siwana samples show that the magma is mantle derived; for the Jalor complex the combined Sr, Nd and Ph data indicate primary mantle derivation with a variable degree of crustal contamination. with the assimilated crust being most likely of Archaean age.The petrogenesis of the two complexes is interpreted as an effect of fractionation of a primary mantle derived magma, simultaneous with assimilation of rocks from the lower crust. The data further document the presence of Archaean crust in the area.

Keywords

Geochronology, Petrology, Malani Igneous Suite, Rajasthan.

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I. M. Bahuguna ¹, B. P. Rathore ¹, Rupal Brahmbhatt ², Milap Sharma ³, Sunil Dhar ⁴, S. S. Randhawa ⁵, Kireet Kumar ⁶, Shakil Romshoo ⁷, R. D. Shah ², R. K. Ganjoo ⁸, Ajai ¹

Affiliations
1 Space Applications Centre, Ahmedabad 380 015, IN
2 M. G. Science Institute, Ahmedabad 380 009, IN
3 School of Social Sciences, Jawaharlal Nehru University, Delhi 110 067, IN
4 Department of Geology, Government College, Dharamshala 176 215,, IN
5 State Council of Science and Technology, Shimla 171 009, IN
6 G.B. Pant Institute of Himalayan Environment and Development, Almorah 263 643, IN
7 Department of Earth Sciences, University of Kashmir, Srinagar 190 006, IN
8 Department of Geology, Jammu University, Jammu 180 006, IN

Abstract

The Himalayan mountain system to the north of the Indian land mass with arcuate strike of NW-SE for about 2400 km holds one of the largest concentration of glaciers outside the polar regions in its high-altitude regions. Perennial snow and ice-melt from these frozen reservoirs is used in catchments and alluvial plains of the three major Himalayan river systems, i.e. the Indus, Ganga and Brahmaputra for irrigation, hydropower generation, production of bio-resources and fulfilling the domestic water demand. Also, variations in the extent of these glaciers are understood to be a sensitive indicator of climatic variations of the earth system and might have implications on the availability of water resources in the river systems. Therefore, mapping and monitoring of these freshwater resources is required for the planning of water resources and understanding the impact of climatic variations. Thus a study has been carried out to find the change in the extent of Himalayan glaciers during the last decade using IRS LISS III images of 2000/01/02 and 2010/11. Two thousand and eighteen glaciers representing climatically diverse terrains in the Himalaya were mapped and monitored. It includes glaciers of Karakoram, Himachal, Zanskar, Uttarakhand, Nepal and Sikkim regions. Among these, 1752 glaciers (86.8%) were observed having stable fronts (no change in the snout position and area of ablation zone), 248 (12.3%) exhibited retreat and 18 (0.9%) of them exhibited advancement of snout. The net loss in 10,250.68 sq. km area of the 2018 glaciers put together was found to be 20.94 sq. km or 0.2% (±2.5% of 20.94 sq. km).

Keywords

Ablation, Glacier, Himalaya, Retreat, Snout.

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Sunil Dhar ¹, Naresh Kochhar ², Rajni Sharma ³, L. N. Gupta ²

Affiliations
1 PG Department of Geology, H.P. University, Regional Centre, Dharamsala, (H.P.) - 176 2 15, IN
2 Department of Geology, Panjab University, Chandigarh, 160 014, IN
3 HCC Ltd., C-1 Works, Tala Hydroelectric Project, PB# 390, Phuentsholing, BT

Abstract

This paper describes mineral chemistry of biotites from Jalor, Tosham and Jhunjhunu ring complexes of Malani igneous suite, India. The chemistry reveals iron enrichment trend in all the biotite samples of the three complexes. FeO*/MgO ratio is the highest (6.72) in Jalor samples whereas lower values of (4.08) and (3.72) have been observed in Tosham and Jhunjhunu samples respectively. Higher MgO has not affected the enhanced proportions of FeO in the biotites of Tosham and Jhunjhunu. Mg ⇌ Fe and 2A1 ⇌ 3Fe²⁺ substitution is dominant in Jalor samples whereas, influence of 3M ⇌ Al is deciphered in the Tosham and Jhunjhunu samples. Most of the biotites fall in the anorogenic (A-type) suites, representing extensional tectonic environment for their host rocks.

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