Mantle-derived fluids in the basement of the Deccan Trap: evidence from stable carbon and oxygen isotopes of carbonates from the Killari borehole basement, Maharashtra, India

We report here for the first time geochemical, mineralogical and stable carbon and oxygen isotopic data on the crystalline basement rocks of the 1993 Killari earthquake region of Maharashtra (India), which is covered by a thick suite of Deccan volcanics. Our results revealed the hitherto unknown amphibolite–granulite nature of the 2.5?Ga basement, which contains 2.00–2.28?wt% of CO₂. The stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopic measurements on carbonates separated from two basement samples KIL-13 (440.5?m depth) and KIL-20 (499.6?m depth) collected from the KLR-1 borehole drilled in the epicentral region showed the respective values of ?6.23 and ?6.22‰ versus PDB for δ¹³C and 7.94 and 8.11‰ versus SMOW for δ¹⁸O. The samples plot in the primary igneous carbonatite field, indicating the mantle origin of the carbonates, derived through the process of mantle metasomatism from the deep mantle carbon reservoir. This would suggest large-scale crust-mantle thermal fluid interaction beneath the Killari seismogenic region, which is characterized by massive upwarping of the high-velocity mafic crust and retrograde metamorphism.     

Sediment Yield Index mapping and prioritization of Madia subwatershed,Sagar District of Madhya Pradesh (India)

Assessment of soil loss through Sediment Yield Index (SYI) is important for watershed planning, prioritization, and development. In the absence of measured sediment data, SYI expressing the relative sediment yield from different basins work as a basis for grading another basin to adopt erosion control measures. An attempt was made to evaluate SYI in wider scale by using cost-effective tools like remote sensing and geographical information system (GIS). SYI was calculated for Madia subwatershed, which consists of 29 microwatersheds and located in Sagar District, Madhya Pradesh (M.P.) The IRS LISS III data and Shuttle Radar Topography Mission (SRTM) digital elevation models (DEM) of 90-m resolution were used to identify land use characteristics and geomorphometric analysis. Major land use was observed as agricultural land (24.7 %), water bodies (16.7 %), forest area (10.2 %), and settlement (21.3 %). In categorization, similar overall accuracy was observed for dense forest, barren land, settlement, and water bodies. The highest SYI with a value more than 20 was observed in microwatershed Mw6, Mw7, and Mw24, which comprises 33 % of the total watershed area. It gives the information about the watershed area that requires very high priority.     

Role of atmospheric ammonia in the formation of inorganic secondary particulate matter: A study at Kanpur,India

Levels of fine Particulate Matter (PM_fine), SO₂ and NO_x are interlinked through atmospheric reactions to a large extent. NO_x, NH₃, SO₂, temperature and humidity are the important atmospheric constituents/conditions governing formation of fine particulate sulfates and nitrates. To understand the formation of inorganic secondary particles (nitrates and sulfates) in the atmosphere, a study was undertaken in Kanpur, India. Specifically, the study was designed to measure the atmospheric levels of covering winter and summer seasons and day and night samplings to capture the diurnal variations. Results showed are found to be significantly high in winter season compared to the summer season. In winter, the molar ratio of to was found to be greater than 2:1. This higher molar ratio suggests that in addition to (NH₄)₂SO₄, NH₄NO₃ will be formed because of excess quantity of present. In summer, the molar ratio was less than 2:1 indicating deficit of to produce NH₄NO₃. The nitrogen conversion ratio (NO₂ to NO₃) was found to be nearly 50% in the study area that suggested quick conversion of NO₂ into nitric acid. As an overall conclusion, this study finds that NH₃ plays a vital role in the formation of fine inorganic secondary particles particularly so in winter months and there is a need to identify and assess sources of ammonia emissions in India.     

High-altitude charged aerosols in the atmosphere of Titan

Observations by several instruments onboard the Cassini spacecraft revealed the existence of heavy hydrocarbon and nitrile species with masses of several thousand atomic mass units in the ionosphere of Titan. These very large molecules are in fact aerosols. The goal of this paper is to compute the concentrations of the charged aerosols in the upper atmosphere (950-1200 km) of Titan. The charging of these aerosols has been studied using the charge balance equations, where positive ions, negative ions, electrons, neutral and charged aerosols are included. Number concentrations of charged aerosols are compared with those observed by the Cassini instruments. The present work estimates the aerosol mass density as 1-10 kg/m³, which is within the predicted range. The results show that the aerosols must be smaller than 10 nm in order to have reasonable agreement with observations by the Cassini Plasma Spectrometer.     

Numerical study for production of space charge within the stratiform cloud

One dimensional numerical model has been developed to predict the production of space charge and variations in other electrical parameters within the low level stratiform type of cloud having very weak vertical motion. Non-linear coupled differential equations which govern ion concentrations, charged and neutral droplet concentrations and electric field were used. Symmetry has been observed in all the electrical parameters within the cloud. The magnitude of average positive ion concentrations was observed to be high as compared to the negative ion concentrations, which is due to low scavenging rate of positive ions than the negative ions, highly attributed to their mobilities. The rate of scavenging of ions affects the concentration of charged droplets, which eventually influence the electric field and thus the space charge density within the cloud. Maximum electric field (E _max) was observed at middle of the cloud whereas minimum was observed at both the edges of the cloud. Minimum electric field (E _min) was found to be equal and constant (∼27 Vm⁻¹) for any drop concentration. Net positive and negative space charges were observed at the top and bottom of the cloud, respectively. The simulated results show some discrepancies to the natural condition, which are due to simulations made under some basic assumptions and limitations and that will be incorporated in the future studies for natural cloud condition.     

Reducing hillslope size in digital elevation models at various scales and the effects on slope gradient estimation

Several models simulate watershed areas by delineating hillslopes. Hillslope size depends on the length of stream tributaries, which are affected by the drainage area threshold (DAT). There is no universal approach to identify the appropriate DAT. Therefore, a method to derive the DAT and a series of steps to delineate a watershed into smaller sizes were proposed in this study, and the impact of hillslope size on slope gradient estimation was investigated. The DAT obtained in this study was smaller than that obtained using other methods, resulting in a shorter length of the tributaries. Dividing these tributaries into equal short segments and using them to delineate the study area reduced the size of the hillslope. The results revealed that the shorter the length of the tributaries, the smaller the hillslope size. The accuracy of gradient estimation increased when the size of the hillslope was reduced.     

Late Pleistocene Paleoflood Deposits Identified by Grain Size Signatures,Parsons Valley Lake,Nilgiris, Tamil Nadu

A study involving grain size analysis was carried out from the Parsons valley lake deposit, Nilgiris, India to determine the depositional environments and paleoflood events since late Pleistocene period (～29,838 cal yr BP). A 72 cm lacustrine core was collected from the lake and eight organic rich sediment samples were AMS radiocarbon dated. The study reveals variations in the grain size distribution chiefly influenced by regional climatic conditions. Paleoflood events have been identified by the individual sedimentary flood signatures of varying changes in the magnitude of sediment supply from the background silty sediment matrix around ～29,838 and ～8405 cal yr BP.