Chrome-diopside Megacryst-bearing Lamprophyre from the Late Cretaceous Mundwara Alkaline Complex,NW India: Petrological and Geodynamic Implications

The occurrence of a rare mantle-derived chrome-diopside megacryst (～8 mm), containing inclusions of olivine, in a lamprophyre dyke from the late Cretaceous polychronous (～100 – 68 Ma) Mundwara alkaline complex of NW India is reported. The olivine inclusions are forsteritic (Fo: 85.23) in composition, and their NiO (0.09 wt%) and CaO (0.13 wt%) contents imply derivation from a peridotitic mantle source. The composition of the chrome diopside (Cr₂O₃: 0.93 wt ) (Wo_45.27 En_48.47 Fs_5.07 and Ac_1.18) megacryst is comparable to that occurring in the garnet peridotite xenoliths found in diamondiferous kimberlites from Archaean cratons. Single pyroxene thermobarometry revealed that this chrome diopside megacryst was derived from a depth range of ～100 km, which is relatively much deeper than that of the chrome-diopside megacrysts (～40–50 km) reported in spinellherzolite xenoliths from the alkali basalts of Deccan age (ca. 66–67 Ma) from the Kutch, NW India. This study highlights that pre- Deccan lithosphere, below the Mundwara alkaline complex, was at least ～100 km thick and, likely, similar in composition to that of the cratonic lithosphere.     

Characterization of Organic Acids in Dew Collected on Surrogate Surfaces

Levels of formate and acetate in dew were measured at Dayalbagh, India, usingsurrogate surfaces. The dew formed per night ranged between 0.06 lm^–2 and 1.38 l m^–2, with an average of 0.59l m^–2. pH ranged between 6.7 and 7.4. Mean concentrations offormate and acetate in dew were 10.2 ± 10.2 eql^–1 and 7.5 ± 4.5 eq l^–1,respectively. The correlation coefficient between the two ions was 0.80 (p =0.001), which suggested that concentrations of these species in dew are linkedtogether. They have either common or different sources with fairly constantstrengths or products of same reaction. Good correlation of formate andacetate with Ca (r = 0.82 and r = 0.70, respectively) and Mg (r = 0.74 and r= 0.71, respectively) suggested that these ions may be associated with Ca andMg after the neutralization process. Deposition rates for formate and acetatein dew per night were 10.2 ± 7.22 mol m^–2 pernight and 4.6 ± 2.2 mol m^–2 per night,respectively. The theoretical Henry's law constant (K^* _H)and the field-observed Henry's law coefficient (K^* _H) ascalculated from concurrent measurements of gas phase and dew for both acidsshowed large discrepancies of three orders of magnitude.     

Trend analysis using discrete wavelet transform (DWT) for long-term precipitation (1851–2006) over India

This study is an attempt to determine the trends in monthly, annual and monsoon total precipitation series over India by applying linear regression, the Mann-Kendall (MK) test and discrete wavelet transform (DWT). The linear regression test was applied on five consecutive classical 30-year climate periods and a long-term precipitation series (1851–2006) to detect changes. The sequential Mann-Kendall (SQMK) test was applied to identify the temporal variation in trend. Wavelet transform is a relatively new tool for trend analysis in hydrology. Comparison studies were carried out between decomposed series by DWT and original series. Furthermore, visualization of extreme and contributing events was carried out using the wavelet spectrum at different threshold values. The results showed that there are significant positive trends for annual and monsoon precipitation series in North Mountainous India (zone NMI) and North East India (NEI), whereas negative trends were detected when considering India as whole.

EDITOR A. Castellarin ASSOCIATE EDITOR S. Kanae     

Textural characteristics,distribution pattern and provenance of heavy minerals in glacial sediments of Schirmacher Oasis,east Antarctica

Heavy minerals of twenty sediment samples, belonging to polar ice sheet, lake, mainland area and shelf region of Schirmacher Oasis, east Antarctica, have been studied for their textural characteristics, abundance and provenance determination. The heavy crop is represented by zircon, tourmaline, rutile, garnet, hypersthene, hornblende, chlorite, enstatite, lawsonite, kyanite, sillimanite, zoisite, andalusite, spinel, topaz and opaques. The assemblage, in general, is dominated by hornblende-hypersthene-garnet assemblage, followed by kyanite-sillimanite-andalusite and zircontourmaline-rutile. The high concentration of specific minerals of metamorphic origin reveals high-grade metamorphic terrain as the primary source. The ZTR ratio is low showing low mineralogical maturity. An attempt has also been made to compare the trends of heavy minerals of various sub glacial regions with those of the average values of entire area.     

Optical properties of some terrestrial rocks and glasses

The optical constants of five naturally occurring rocks have been determined in the spectral range between 0.2 and .50 μm. Between 0.2 and 5 μm, the real and imaginary parts of the index of refraction were found from a combination of reflectivity and transmission measurements by using Beer's law and the Fresnel reflectivity equation. At wavelenths beyond 5 μm only reflectivity measurements could be made and both constants were found from an application of classical dispersion theory. These optical constants will be valuable for studies of the interaction of light with rock surfaces, atmospheric dust and interplanetary and interstellar dust grains.     

Neutrino degeneracy and the primordial abundance of helium and deuterium

Recent observations indicate that the primordial abundance of⁴He could be smaller than 0.24. It may then be necessary to invoke neutrino degeneracy in the early universe to explain the primordial abundances of helium and deuterium. It is shown here that the necessary degeneracy, though small, gives rise to a large asymmetry between the present number densities of neutrinos and antineutrinos. The effect of degeneracy on the upper limit to the neutrino masses is also considered.     

Spatio-temporal trends of rainfall across Indian river basins

Theoretical and Applied Climatology - Daily gridded high-resolution rainfall data of India Meteorological Department at 0.25° spatial resolution (1901–2015) was analyzed to detect the...