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[en] It was found that thermoluminescence (TL) in zircons fades anomalously. Several factors that could affect the rate of anomalous fading were also studies. It was determined that grain size, dose rate and total dose received by the sample did not have any significant effect on the rate of anomalous fading. However annealing of the sample (approx 900deg C for 1 hr in air) or its storage at different temperature (well below the peak temperature) seems to affect, at least, the fast component part of the anomalous fading TL. This component can also be removed by infra-red light
[en] Reactions of natural zircon with Na2CO3 with mole ratios ranging from 1:1 to 1:2.6 were studied at 800 and 900 degC for periods up to 48 hours. The products of the reaction were Na2ZrO3, Na2SiO3 and Na2ZrSiO5. A reaction mechanism, valid within the range of temperature of this study, has been proposed on the basis of the relative proportions of the co-existing phases as a function of composition, temperature and time. The reaction was initiated with the formation of Na2ZrSiO5 which later reacted with any excess Na2CO3 present resulting in the formation of Na2ZrO3 and Na2SiO3. When treated with water, Na2ZrSiO5 remained unaffected while Na2ZrO3 was converted to amorphous hydrated zirconia. (author)
[en] In order to characterize inhomogeneities in monolithic ceramics, signal characterization of backscattered 25 MHz focussed, pulsed ultrasound has been applied in a step by step approach. The first step was to examine voids in glass. These were optically characterized as spheres with diameters of 30 to 120 μm. Correlations were made with the ultrasonic signals returned. A mathematical model for ultrasound scattering from spheres in an elastic medium based on Ying and Truell's work was used to predict the frequency response characteristics for voids. The next step involved the manufacture of spherical particles of zirconia in the size range of 20 to 200 μm diameter which were also imbedded in glass. The model was modified to calculate the backscattering of ultrasound from inhomogeneities of known elastic constants. The most recent step was the introduction of spherical inclusions into crystallizable glass. Optical characterization was made, then the glass was crystallized to introduce a host matrix structure similar to that of a ceramic. Using appropriate values for elastic constants, experimental and theoretical results are found to be well correlated. This presentation review the work down on inhomogeneities in glasses and its application to defect characterization in ceramics
[en] This paper presents the results of U–Pb (LA-ICP-MS) and Lu–Hf isotope studies of detrital zircons from the presumably Permian meta sedimentary rocks of the Tokur terrane. It has been established that the grains of detrital zircons from the meta sedimentary rocks of the Tokur and Ekimchan formations have a similar age distribution, which indicates the similar (or equal) age of these formations. The youngest zircons in these rocks has a U–Pb age of 326–323 Ma, which determines the lower age limit of the protolith of the rocks. The upper age limit of the formations corresponds to 254–251 Ma, which is the age of the Late Permian granitoids intruded into these formations. The main sources of zircon in the meta sedimentary rocks of the Tokur terrane are the igneous and metamorphic massifs of the southeast framing of the North Asian Craton. The Tokur terrane can be considered as a fragment of the Paleozoic accretionary complex, formed near the southeastern margin of the North Asian Craton.
[en] Beaches are the main sources for economic heavy minerals (HM) like ilmenite rutile, monazite, zircon, garnet and sillimanite. The seasonal HM accumulations, colloquially called 'beach washings' are mined by IREL and KMML in Kerala and by IREL and several private enterprises in Tamil Nadu. These sediments are found to contain 85-90% THM. It is presumed that during the monsoon, the sea is agitated and the churning and spiralling action of water lifts HM-bearing sediments from the sea floor and transports in suspension and deposits on the beach berm, the backwash taking the relatively lighter part of the sediment load back into the sea. This process is thought to give rise to HM-enriched sand on the beach face and the swash plain. It is pertinent to understand the controls on these economically important and scientifically interesting processes. Beachface is the seaward section of a beach exposed to and shaped by the action of waves. The beach face is the zone of most active change. Berm is the terrace of a beach that has formed in the backshore, above the water level at high tide. Berms are commonly found on beaches that have fairly coarse sand and are the result of the deposition of material by low energy waves. On broad beaches there may be three or more sub-parallel berms, each formed under different wave conditions. Swash zone is defined as that part of the beach extending from a nearshore shallow depth to the limit of maximum inundation; is a relatively narrow region of great importance for the exchange of sediment between land and sea. Morphological processes such as storm-induced erosion, post-storm recovery, seasonal variation in foreshore shape, and evolution of rhythmic
[en] Study of the distribution peculiarities of elements-impurities in zircons shows that they form in the medium corresponding to a closed system. Only in case of reverse geochemical zoning it is possible to assume diffusion losses of uranium out of zircons. In all other cases ''non-exclussiveness'' of the system depends on external factors which may be predicted. In this case the discordancy will be regarded as an expected phenomenon which may be taken into account in the zircon geochronology
[en] In order to resolve the age of Navysh volcanics (NV), which is usually attributed to the Lower Riphean of the Ai Formation, we have used geochronological, petrologic, and mineralogical methods of zirconology, apart from the SHRIMP isotopic data of single zircon grains. Moreover, TIMS isotope age analyses have been conducted, the results of which can be regarded as both controlling and providing the most correct information. The TIMS and SHRIMP data make it possible to suggest a polychronous character of the NV, which include not only Riphean, but also Paleozoic groups of volcanics. In this situation, an assessment of the scales of such polychroneity of NV and, correspondingly, of the Ai Formation as a whole becomes urgent.
[en] The results of U–Th–Pb geochronological study indicate that the youngest peaks on the relative probability curves of the age obtained for the Un’ya-Bom terrane correspond to ages of 207 and 212 Ma. These values were obtained for zircons from the meta-aleurolite samples from the Kurnal and Amkan formations, respectively. Similar age estimates for the youngest peaks were also obtained in the case of detrital zircons from the metasedimentary rocks of the Tukuringra terrane in the eastern part of the Mongol–Okhotsk fold belt, which indicates that, within the belt, Lower Mesozoic flyshoid complexes are much more widespread than was assumed. Based on the geochronological and Sm–Nd isotopic data obtained, it was shown that the material was carried to the sedimentation basin mainly from the continental massifs of the Amur superterrane.