• Rajeev Kumar

      Articles written in Journal of Earth System Science

    • Monitoring and evaluation of seasonal snow cover in Kashmir valley using remote sensing, GIS and ancillary data

      H S Negi N K Thakur Rajeev Kumar Manoj Kumar

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      Seasonal snow cover is a vital natural resource in the Himalaya. Monitoring of the areal extent of seasonal snow cover is important for both climatological studies as well as hydrological applications. In the present paper, snow cover monitoring was carried out to evaluate the region-wise accumulation and ablation pattern of snow cover in Pir Panjal and Shamshawari ranges of Kashmir valley. The study was carried out for the winter period between November and April of 2004–05, 2005–06 and 2006–07, using multi-temporal WiFS sensor data of IRS-1C/1D satellites. The study shows reduction in the areal extent of seasonal snow cover and rising trend of maximum temperature in three winters for the entire Kashmir valley. This has been validated with 20 years (1988– 89 to 2007–08) climatic conditions prevailed in both ranges of Kashmir valley. Region-wise study shows the spatial and temporal variability in seasonal snow cover within Kashmir valley. Advance melting was observed in Banihal and Naugam/Tangdhar regions than Gurez and Machhal regions. Different geographical parameters of these regions were studied to evaluate the influence on snow cover and it was observed that altitude and position of region with respect to mountain range are the deciding factors for retaining the seasonal snow cover for longer duration. Such region-wise study of snow cover monitoring, can provide vital inputs for planning the hydropower projects, development in habitat areas, recreational and strategic planning in the region.

    • Apatite and zircon fission-track thermochronology constraining the interplay between tectonics, topography and exhumation, Arunachal Himalaya

      JAMES PEBAM VIKAS ADLAKHA A K JAIN R C PATEL NAND LAL S SINGH RAJEEV KUMAR RAHUL DEVRANI

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      Thirty-eight new apatite and zircon fission-track ages from 26 bedrock samples vary from 2.0 $\pm$ 0.3 to 12.1 $\pm$ 1.2 Ma, and 3.3 $\pm$ 0.3 and 13.2 $\pm$ 0.7 Ma, respectively, along three transects of the Kurung, Subansiri, and Siyom Rivers, which flow across the major structures of the Arunachal Himalaya. These cooling ages reveal marked variations in millennial-scale ( >10$^{5}$ yr) exhumation rates from 0.6 to 3.0 mm/yr. A distinct positive correlation is visible between local topographic relief, hill slopes, channel steepness, and exhumation rates. The cooling ages are younger in the northern antiformal domains and older within the synformal nappe along the mountain front. Thermal modelling and time–temperature paths suggest that zones of rapid exhumation are controlled by structural windows within the Lesser Himalaya that were developed between 8 and 6 Ma over blind Main Himalayan Thrust (MHT). This time of rapid rock uplift and major topographic change led to a two-fold increase in the exhumation rates in the northern antiformal domains than the southern front of Arunachal Himalaya. Variation in cooling ages does not correlate with the present-day precipitation pattern. Tectonics appears to be the leading factor in driving the exhumation rates and landscape evolution in the Arunachal Himalaya.

    • P–Ͳ estimates for the fractionated and primary melt of tholeiitic dykes from Multai area of Deccan flood basalt, Madhya Pradesh (India)

      RAJEEV KUMAR TALAT AHMAD ASHIMA SAIKIA

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      Petrological, mineral chemical and geochemical results are reported for the Cenozoic en-echelon tholeiitic dykes of the Multai area of Deccan flood basalt province, Madhya Pradesh (India) to estimate the pressure and temperature of fractionated and primary melt for these dykes. The rocks are composed of plagioclase, augite and olivine phenocrysts set in a holocrystalline groundmass of plagioclase microlites, augite, Ti–magnetite, ilmenite and interstitial glass. Plagioclases are labradorite in composition (An$_{48–70}$), and pyroxenes are augite with a composition of Wo$_{24–40}$, En$_{24–52}$ and Fs$_{13–56}$. Forsterite (Fo) contents of olivine phenocrysts range from Fo$_{51}$ to Fo$_{73}$. These tholeiitic dykes are rich in Al$_2$O$_3$, Rb, Ba and Sr and show enrichment in light rare-earth element relative to heavy rare-earth element with respect to enriched mid-ocean ridge basalt and normal mid-ocean ridge basalt. Studied samples have lower Ni, Cr, Co and MgO contents than primary compositions suggesting evolved nature of these rocks. The Sr–Nd isotopic ratios of the studied dyke samples indicate a Dnity to the Mahabaleshwar and Poladpur formations of the southwestern Deccan stratigraphy and the positive εNd(t) values suggest depleted mantle source. The fractionated melt for these dykes last equilibrated at P = 0.2–4.4 kbar and Ͳ = 1128–1169°C before the eruption, based on olivine, clinopyroxene and plagioclase mineral-melt equilibria thermo-barometers. The estimated mantle source and primary melt compositions suggest melting in the spinel stability field (P${\le}$28 kbar). It was followed by melt equilibration with mantle olivine Fo$_{89.6}$ at P = 18–22 kbar and Ͳ = 1419–1463°C. The evaluation of whole-rock geochemistry and mineral chemistry supports the hypothesis of fractional crystallisation of plagioclase + clinopyroxene ± olivine ± Fe–Ti oxides for the evolution of these basaltic dykes

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