Magnetic susceptibility mapping of felsic magmatic lithounits in the central part of Bundelkhand Massif,central India

Late Archaean to Palaeoproterozoic felsic magmatic lithounits exposed in the central part of the Bundelkhand massif have been mapped and their redox series (magnetite vs ilmenite series) evaluated based on magnetic susceptibility (MS) data. The central part of Bundelkhand massif comprises of multiple felsic magmatic pulses (∼2600–2200 Ma), commonly represented by coarse grained granite (CGG-grey granite, CPG-pink granite), medium grained pink granite (MPG), fine grained pink granite (FPG), grey and pink rhyolites and granite porphyry (GP). However, the pink colour of these felsic rocks is the result of hydrothermal fluid-flushing leading to potassic alteration of grey granites. MS values of CGG vary from 0.058 to 14.75×10⁻³ SI with an average of 6.35×10⁻³ SI, which mostly represent oxidized type, magnetite series (73%) granites involving infracrustal (igneous) source materials. CPG (av. MS=3.95×10⁻³ SI) is indeed a pink variety of CGG, the original oxidizing nature of which must have been similar to the bulk of CGG, but has been moderately to strongly reduced because of distinctly more porphyritic nature together with partial assimilation of metapelitic (supracrustal) materials, surmicaceous enclaves, carbonaceous material included in the source materials, and to some extent, induced by hydrothermal and later deformational processes. MPG (av. MS= 1.15×10⁻³ SI) as lensoidal stock-like bodies intrudes the CPG and represent both magnetite series (18%) and ilmenite series (82%) granites, which are probably formed by heterogeneous (mixed) source rocks. GP (av. MS=6.26×10⁻³ SI) occur as dykes (mostly trending NE-SW) intrudes the MPG, CPG and migmatites and bears the nature similar to oxidized type, magnetite series granite. FPG (av. MS= 0.666×10⁻³ SI) trending NE-SW occur as lensoid bodies including a large outcrop, is intrusive into both CPG and MPG, and is moderately to very strongly reduced type, ilmenite series granites, which may be derived by the melting of metapelitic crustal sources. FPG hosting microgranular (mafic magmatic) enclaves commonly exhibit high MS values (7.31–10.22×10⁻³ SI), which appear induced by the mixing and mingling of interacting felsic and mafic magmas prevailed in an open system. Grey (av. MS=10.30×10⁻³ SI) and pink (av. MS=6.72×10⁻³ SI) rhyolites represent oxidized type, magnetite series granites, which may have been derived from infracrustal (magmatic) protoliths. Granite series evaluation of felsic magmatic rocks of central part of Bundelkhand massif strongly suggests their varied redox conditions (differential oxygen fugacity) mostly intrinsic to magma source regions and partially modified by hydrothermal and tectonic processes acting upon them.     

Application of the WEPP model for prioritization and evaluation of best management practices in an Indian watershed

The pre‐calibrated and validated physically based watershed model, water erosion prediction project (WEPP) was used as a modelling tool for the identification of critical watersheds and evaluation of best management practices for a small hilly watershed (Karso) of India. The land use/cover of the study area was generated using IRS‐1C LISS‐III (linear imaging self scanner) satellite data. The watershed and sub‐watershed boundaries, drainage, slope and soil map of the study area were generated using ARC/INFO geographic information system (GIS). The WEPP model was finally applied to the Karso watershed which lies within Damodar Barakar catchment of India to identify the critical sub‐watersheds on the basis of their simulated average annual sediment yields. Priorities were fixed on the basis of ranks assigned to each critical sub‐watershed based on the susceptibility to erosion. The sub‐watershed having the highest sediment yield was assigned a priority number 1, the next highest value was assigned a priority number 2, and so on. Subsequently, the model was used for evaluating the effectiveness of best management practices (crop and tillage) for conservation of soil for all the sub‐watersheds. On the basis of this study, it is realized that cash crops like soyabean should be encouraged in the upland portion of the sub‐watersheds, and the existing tillage practice (country plough/mould board plough) may be replaced by a field cultivation system for conservation of soil and water in the sub‐watersheds. Copyright © 2009 John Wiley & Sons, Ltd.     

Atmospheric temperature profile for a tropical region from TIROS-N microwave sounding unit

Atmospheric temperature profiles have been derived using 53·74 GHz, 54·96 GHz and 57·95 GHz channels data from the Microwave Sounding Unit onboard TIROS-N. For this purpose regression coefficients have been derived using MONEX-79 radiosonde data during the period May to July 1979. The temperature profiles derived at a few selected places were closer to radiosonde profiles than the profiles derived using standard regression coefficients for the tropical region supplied by NOAA.     

Terrestrial heat flow in the North Island of New Zealand

Large variations in terrestrial heat flow from 21 to 209 mW/m² have been observed over the North Island, New Zealand. This is generally in good agreement with the pattern of existing geological and geophysical observations. A high heat flow zone with a value of 92 ±3 mW/m², which corresponds to melting temperatures near the base of the crust, is delineated in the northern part of the Taranaki Basin. In the rest of the island, heat flow appears to be low to normal, but some isolated high values are also found. Observed results are interpreted in terms of crust and mantle structure in a region of plate subduction.     

Correlation analysis of geothermal data for the sedimentary basins of India

Correlation coefficients are calculated from the available geothermic data for the sedimentary basins of India to reveal some significant association between: (1) heat flow and thermal conductivity, (2) heat flow and geothermal gradient, (3) geothermal gradient and thermal conductivity, and (4) heat flow and related crustal thickness. The observed negative correlationship between heat flow and thermal conductivity for all Indian sedimentary basins suggests corresponding changes in crustal thickness.     

Changes in the source and transport mechanism of terrigenous input to the Indian sector of Southern Ocean during the late Quaternary and its palaeoceanographic implications

Changes in the terrigenous sediment source and transport mechanisms during the late Quaternary have been investigated using four sediment cores within the Indian sector of Southern Ocean, using the magnetic susceptibility (MS) and sedimentological records. Sediments deposited during the Holocene and other interglacial periods were characterised by low MS, low sand content, reduced ice-rafted detritus (IRD) input and increased illite possibly transported via hydrographic advection from the south. The glacial intervals are characterised by high MS, high sand content, increased IRD input and reduced illite clays, derived from both local as well as Antarctic sources. Significant reduction in clay fraction and illite content during glacials suggests that the erosive and transporting capabilities of the deep and bottom waters could have reduced compared to the interglacial times. The changes in terrigenous influx to this region were significantly influenced by the rhythmic glacial-interglacial fluctuations in bottom circulation and the position of the Polar Front.     

Geomorphological study of sundarban deltaic estuary

Study of landforms in Sundarbans deltaic estuary is necessary in regular basis due to its importance and impact on ecology, climate and economy. Remote sensing has proved as an important tool to study this. Multi-temporal satellite data helps to delineate the various geomorphic classes in different time domain and also provide inputs to study the coastal erosion and accretion. Finer spatial and better temporal resolution will be an added adventure for this kind of study.