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Singhbhum craton in eastern India is one of the oldest and perhaps geologically and geophysically most complex geological terrains on the surface of the Earth, containing a number of intra-cratonic Archean volcanic suites. In the present study, we investigate Mesoarchean volcanic rocks of the Simlipal complex, a tiger reserve in the Mayurbhanj district of Odisha (India). Our results provide a new understanding of the regional geodynamic scenario of the Eoarchean Singhbhum craton, including the nature of plume–lithosphere interaction based on the detailed analysis of geological, geochemical and geophysical data. Whole-rock geochemical studies exhibit large variation in SiO2 (39.30–60.57 wt%), TiO2 (0.20–1.55 wt%), Al2O3 (4.45–15.63 wt%), MgO (5.25–37.00 wt%) and CaO (3.46–11.26 wt%) with low to moderately high Cr (50–1503 ppm) and Ni (36–550 ppm) contents. These rocks are cumulates to porphyritic and petrographically and geochemically, can be classified as ultramafic (lherzolite, pyroxenite), picrite, basalt, basaltic andesite, andesite and boninite. Their trace elements and HFSE/REE patterns indicate that they belong to the same parental magma. Rare earth elements and trace element patterns exhibit moderate fractionation with a coherent pattern of (La/Yb)n: 1.38–8.50, (Gd/Yb)n: 0.92–2.59 and (La/Sm)n: 1.11–4.40, consistent with polybaric melting. The present study suggests that these rocks were generated by decompressive melting of a mantle plume head at a depth of garnet to spinel lherzolite field together with fractional crystallization and crustal contamination in the subcontinental lithospheric mantle (SCLM), which is corroborated by the highly uplifted nature of this terrain, associated with positive gravity anomalies. This plume had a mantle potential temperature between 1400 and 1700 °C and pressure reaching 4.4 GPa. Massive upwarping of the lower crust to an extremely shallow depth of about 4 km from the surface, 21 km thick magmatic underplating above the Moho and the lithosphere asthenosphere boundary at 81 km, would support plume-induced active crust–mantle thermal interaction and extremely warm and deformed nature of the lithosphere beneath the Simlipal volcanic complex. Based on the findings of millerite (NiS), quench/spinifex texture and shock metamorphic features in these volcanic rocks, we infer that there could be a possibility that the suggested mantle plume in the study area may have been triggered by an asteroidal impact. [ABSTRACT FROM AUTHOR]

The radiolarian cherts of Late Cretaceous age are reported in the Andaman-Nicobar ophiolites of Bay of Bengal, India. They are of chocolate-coloured (Type-I) and light pink-coloured (Type-II) varieties, juxtaposed and tectonically associated with phyllites, claystones and basalts and are exposed in eastern part of North Andaman Island. These cherts are composed of radiolarian tests in a fine-grained ferruginous matrix. Type-I radiolarian cherts have low SiO2, and high Al2O3, Fe2O3(T), MgO, Na2O and TiO2 and trace elements as compared to Type-II cherts. Al–Fe–(∑REE–Ce) diagram of the studied cherts indicates a mixed terrigenous and volcanogenic source. LaN/CeN ratios (0.76–0.89 for Type-I and 0.71–0.88 for Type-II) and Ce-anomalies (Ce/Ce* = 1.15–1.33 for Type-I and 1.07–1.38 for Type-II) and other elemental ratios in these cherts suggest that they were deposited in continental margin environments. It has been suggested that the studied samples of cherts were deposited at different places, were scrapped off the subducting plate, became tectonically juxtaposed. They were obducted onto the leading edge of the Eurasian continent during the Late Cretaceous prior to the currently active Andaman–Java subduction, that was probably initiated during the Late Miocene. [ABSTRACT FROM AUTHOR]

Hyaloclastites and pillow breccias are exposed in the northeastern part of the lower pillow basalt, which constitutes a part of the Andaman ophiolitic sequence, in the southern part of South Andaman Island. The hyaloclastite bands are composed of glass shards and basaltic fragments in a fine-grained matrix. The lower pillow basalts, in which hyaloclastites occur, are tholeiitic in nature with MORB affinity and slightly LREE-depleted REE pattern. However, their slight LREE depletion and high Ba/Zr ratios (0.23-0.42) relative to N-MORB and LILE (K, Rb, Ba and Sr) enrichment suggest their back-arc basin basalt affinity. The majority of the glass shards and basaltic fragments in these hyaloclastites have planar surfaces compared to those which have concave outer surfaces and vesicular nature, suggesting that these hyaloclastites were produced by a relatively gentle process rather than by explosive magma-water action in an oceanic setting. [ABSTRACT FROM AUTHOR]

The Andaman ophiolites are well exposed in the Andaman group of islands, which is part of the Sunda-Burmese double-chain arc system in the Bay of Bengal, India. Plagiogranites occurring on the eastern margin of the southern part of South Andaman Island appear as interstitial vermicular and micrographic intergrowths of quartz and plagioclase. They are tonalitic to trondhjemitic in composition, and their Rb, Yb, Ta, and Y abundances are characteristic of a volcanic-arc affinity. Sensitive high-resolution ion microprobe U-Pb dating of zircons from a plagiogranite within the Andaman ophiolite has yielded a weighted mean 206Pb/238U age of 93.6 ± 1.3 Ma, interpreted as the age of its crystallization. The subduction-related plagiogranite has intruded a gabbro unit of the Andaman ophiolites as well as extrusives of the East Coast Volcanics at this time. Since the Andaman ophiolitic rocks predate the plagiogranite, they cannot have been generated in the currently active Late Miocene Andaman-Java subduction zone and were most likely obducted onto the leading edge of the Eurasian continent at an earlier phase of subduction activity during early Cretaceous time. [ABSTRACT FROM AUTHOR]

Self-organized construction of advanced materials and devices has been carried out starting with tailor-made colloidal nanoparticles as building blocks. Multilayer thin films of gold nanoparticles stabilized by glutamates and zinc sulfide nanoparticles capped with chitosan were self-organized by a modified polyelectrolyte deposition process. Resistive current-voltage characteristic was observed in devices (less than 50 layers). The conduction onset in thicker devices (>50 layers) was found to be at applied voltages of ∼1.6, ∼1.94, and ∼2.79 V for 75, 100, and 150 layer structures, respectively. Devices exhibit similar behavior in forward and reverse biases and the electrical characteristics were repeatable. [ABSTRACT FROM AUTHOR]

The article discusses research findings on the occurrence of ash layers in radiolarian cherts in south Andaman Island which suggests explosive volcanic activity during the Late Cretaceous period. The main rock types of the Andaman-Nicobar Islands and the two distinct types of the Late Cretaceous volcanic rocks are cited. A description and analysis of the occurrence of radiolarian cherts in the island is presented.

New geological and geochemical data have been presented in this paper to improve the understanding of the petrogenesis and regional geodynamic evolution of the 2.8–2.5 Ga Dhanjori volcanics. These volcanics exhibit porphyritic texture and classified as picritic basalt. The Dhanjori volcanics are MgO-rich (9.97–15.81 wt%) with moderate SiO2 (51.62–53.82 wt%), FeOT (9.97–12.57 wt%) and TiO2 (0.73–1.21 wt%) but relatively higher Ni (123.56–545.35 ppm) and Cr (241.87–1158.41). The rare earth element (REE) patterns and their ratios indicate their derivation from the garnet to spinel stability field due to decompressive melting of a mantle plume head near the crust-mantle boundary, which is supported by the presence of high positive gravity anomaly over the Dhanjori lavas. The thermobarometric studies indicate that the primary magma had an initial mantle potential temperature between 1350 and 1500°C in a pressure range of 1 to 1.8 GPa, thus conforming with the mantle origin, which is further endorsed by supplementary geophysical studies. [ABSTRACT FROM AUTHOR]

Graphene is a two-dimensional material with a capability of gas sensing, which is here shown to be drastically improved by inducing gentle disorder in the lattice. We report that by using a focused ion beam technique, controlled disorder can be introduced into the graphene structure through Ga+ ion irradiation. This disorder leads to an increase in the electrical response of graphene to NO2 gas molecules by a factor of three in an ambient environment (air). Ab initio density functional calculations indicate that NO2 molecules bind strongly to Stone–Wales defects, where they modify electronic states close to the Fermi level, which in turn influence the transport properties. The demonstrated gas sensor, utilizing structurally defected graphene, shows faster response, higher conductivity changes and thus higher sensitivity to NO2 as compared to pristine graphene. [ABSTRACT FROM AUTHOR]

The objectives of this study were to assess the proportion of hepatitis C virus (HCV) reactors and to identify risk factors associated with HCV infection in volunteer blood donors in Karachi, Pakistan. Between 1 January 1998 and 31 December 2002, consecutive blood donations tested at two blood banks were used to assess the proportion of HCV sero-reactors donors. To evaluate the potential risk factors, a case-control study design was implemented to select cases and controls between 15 October 2001 and 15 March 2002. The overall seroprevalence of HCV in these blood donors was 1.8% (6349/35 1309). Trend analysis revealed a significant (P < 0.001) linear increase in proportions of HCV-seropositive donors from 1998 to 2002. Final multivariate logistic regression model showed that the cases were more likely than controls to have reported past hospitalization or to have received multiple injections. When a glass syringe was used to give therapeutic injections, it increased the adjusted odds of being HCV seropositive significantly more among cases than in controls and this relationship was stronger when injection was given by general medical practitioner than if the injection was given in hospital setting. Cases were more likely than controls to have reported sexual contact with multiple sexual partners. Primary prevention programmes focused on identified risk factors might help to curtail the spread of HCV infection in this community and in other similar settings in developing countries. [ABSTRACT FROM AUTHOR]