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Dubey C.P.,CSIR - Central Electrochemical Research Institute | Tiwari V.M.,CSIR - Central Electrochemical Research Institute | Tiwari V.M.,National Center for Earth Science Studies
Computers and Geosciences | Year: 2016

New measuring instruments of Earth's gravity gradient tensors (GGT) have offered a fresh impetus to gravimetry and its application in subsurface exploration. Several efforts have been made to provide a thorough understanding of the complex properties of the gravity gradient tensor and its mathematical formulations to compute GGT. However, there is not much open source software available. Understanding of the tensor properties leads to important guidelines in the development of real three dimensional geological models. We present a MATLAB computational algorithm to calculate the gravity field and full gravity gradient tensor for an undulated surface followed by regular geometries like an infinite horizontal slab, a vertical sheet, a solid sphere, a vertical cylinder, a normal fault model and a rectangular lamina or conglomerations of such bodies and the results are compared with responses using professional software based on different computational schemes. Real subsurface geometries of complex geological structures of interest are approximated through arrangements of vertical rectangular laminas. The geological application of this algorithm is demonstrated over a horst-type structure of Oklahoma Aulacogen, USA and Vredefort Dome, South Africa, where measured GGT data are available. © 2015 Elsevier Ltd. Source


Harley S.L.,University of Edinburgh | Nandakumar V.,National Center for Earth Science Studies
Precambrian Research | Year: 2016

In-situ zircon U-Pb isotopic and monazite Th-U-Pb chemical ages from leucosome in migmatitic paragneiss at Kanjampara in the Trivandrum Block, India, demonstrate the occurrence of high-T metamorphism and anatexis at 1.92 Ga. This Palaeoproterozoic tectonothermal event was strongly overprinted by the main Neoproterozoic-Cambrian granulite facies tectonism which itself involved significant partial melting and formation of garnet-bearing assemblages at 0.65 GPa and >820-860 °C. Monazite grains, which enclose zircon grains and locally preserve Palaeoproterozoic chemical age domains, were extensively reset and recrystallized at 565 ± 6 Ma. These monazite grains were further modified to form high-Th cuspate rims at 517 ± 15 Ma, equivalent to the lower intercept age for extensive Pb-loss from the highly discordant 1.92 Ga zircon, 528 ± 18 Ma. These results confirm that at least some of the metasedimentary paragneisses in the Trivandrum Block are polymetamorphic, initially metamorphosed in the Palaeoproterozoic in an event older than the 1.89-1.85 Ga granitic orthogneisses recognised from the area. The nature of the relationship between the paragneisses and older (2.0-2.1 Ga) granitic and charnockitic orthogneisses of the Trivandrum and Nagercoil Blocks, in particular whether they share the same Palaeoproterozoic history or were interleaved after 1.92 Ga, requires further investigation focussed on the presence or absence of the isotopic imprint of this event in both rock suites throughout the area.The growth or recrystallisation of monazite at ca. 565 Ma and its further modification at ca. 520 Ma indicates that the high-T metamorphism in the Pan-African was long-lived, with a duration of at least 45 Myr. This adds further weight to recent proposals, based on zircon-monazite isotopic studies from other localities in the Trivandrum Block, that the region formed the mid- to deep-crust of a long-lived collisional hot orogenic belt that welded Gondwana from ca. 580-510 Ma. © 2016 . Source


Joseph B.,P.A. College | Prasanth C.S.,National Center for Earth Science Studies | Prasanth C.S.,University of Washington | Jayanthi J.L.,National Center for Earth Science Studies | And 4 more authors.
Journal of Biomedical Optics | Year: 2015

The aim of this study was to evaluate the applicability of laser-induced autofluorescence (LIAF) spectroscopy to detect and quantify dental plaque. LIAF spectra were recorded in situ from dental plaque (0-3 grades of plaque index) in 300 patients with 404 nm diode laser excitation. The fluorescence intensity ratio of the emission peaks was calculated from the LIAF spectral data following which their scatter plots were drawn and the area under the receiver operating characteristics were calculated. The LIAF spectrum of clinically invisible grade-1 plaque showed a prominent emission peak at 510 nm with a satellite peak around 630 nm in contrast to grade 0 that has a single peak around 500 nm. The fluorescence intensity ratio (F510/F630) has a decreasing trend with increase in plaque grade and the ratio values show statistically significant differences (p < 0.01) between different grades. An overall sensitivity and specificity of 100% each was achieved for discrimination between grade-0 and grade-1 plaque. The clinical significance of this study is that the diagnostic algorithm developed based on fluorescence spectral intensity ratio (F510/F630) would be useful to precisely identify minute amounts of plaque without the need for disclosing solutions and to convince patients of the need for proper oral hygiene and homecare practices. © 2015 Society of Photo-Optical Instrumentation Engineers. Source


Noujas V.,National Center for Earth Science Studies | Thomas K.V.,National Center for Earth Science Studies | Badarees K.O.,National Center for Sustainable Coastal Management
Ocean Engineering | Year: 2016

Coastal processes along the Munambam to Chettuwa coastline located at the south-west part of India have been studied to understand the role of a mudbank and artificial structures like breakwaters in causing shoreline changes. The mudbank occurring along this coast is different from those in South America, Lousiana and China. The morphology and coastal processes of the coast have been studied by collecting nearshore and beach data from 2009 to 2013. Location of the mudbank area has been shifting over the years from north to south. The beach at the mudbank and its north is accreting while the southern side is eroding. Harbor breakwaters and seawalls are other factors influencing beach stability. An erosion hotspot along this mudbank coast is identified and management interventions proposed based on numerical model studies using MIKE 21 SW model and LITPACK. The model results are calibrated and validated with field observations. Sediment transport along this sector was estimated using LITDRIFT module. Shoreline change was calculated using the LITLINE module. The production run was carried out with different management options and the most suitable option is recommended for the eroding sector. The other sectors do not require any intervention to sustain the beaches. © 2015 Published by Elsevier Ltd. Source


Kroner A.,Chinese Academy of Geological Sciences | Kroner A.,University of Mainz | Santosh M.,China University of Geosciences | Hegner E.,Ludwig Maximilians University of Munich | And 9 more authors.
Gondwana Research | Year: 2015

SHRIMP dating of magmatic zircons from granitoid gneisses and charnockites of the Trivandrum and Nagercoil Blocks in the granulite terrane of southernmost India yielded well-defined protolith emplacement ages between 1765 and ca. 2100Ma and also document variable recrystallization and/or lead-loss during the late Neoproterozoic Pan-African event at around 540Ma. Hf-in-zircon and whole rock Nd isotopic data suggest that the granitoid host rocks were derived from mixed crustal sources, and Hf-Nd model ages vary between 2.2 and 2.8Ga. A gabbroic dyke, emplaced into a charnockite protolith and deformed together with it, only contained metamorphic zircon whose mean age of 542.3±4.0Ma reflects the peak of granulite-facies metamorphism during the Pan-African high-grade event. The Sm-Nd whole-rock isotopic system of several granitoid samples dated in this study was significantly disturbed during granulite-facies metamorphism, most likely due to a CO2-rich fluid phase. Whole-rock Nd model ages are consistently older than zircon-derived Hf model ages.The Trivandrum and Nagercoil Blocks are reinterpreted as a single tectono-metamorphic terrane predominantly consisting of Palaeoproterozoic granitoids interlayered with supracrustal rocks that must be older than ca. 2100. Ma. Ductile deformation, migmatization and anatexis have obliterated the original rock relationships. These blocks probably have their counterpart in the Highland Complex of neighbouring Sri Lanka and in the high-grade Palaeoproterozoic terrane of southern Madagascar. We speculate that the southern Indian khondalites may have their counterparts in the khondalite belt of the North China Craton. © 2014. Source

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