At Fraser Lakes Zone B, the pegmatites and leucogranites intrude the deformed contact between Paleoproterozoic metasedimentary gneisses of the Wollaston Group and Archean orthogneisses, and have characteristics typical of the Abyssal pegmatite subclass. For two examples of Group-A U- and Th-enriched pegmatite and leucogranite, and two examples of Group-B Th- and LREE-enriched pegmatite and leucogranite samples that have minimal petrographic evidence of later alteration, we analyzed selected minerals by electron microprobe to provide constraints on the age and temperature of intrusion. The Group-A pegmatites contain uraninite with variable CaO and SiO2, indicative of later recrystallization, uranoan thorite spatially associated with complexly zoned zircon with some intermediate solid-solution between the two minerals , rare coffinite, and titaniferous magnetite and ilmenite where they intrude the Archean orthogneisses. CHIME dating of the most pristine uraninite yielded ages between 1. The Group-B pegmatites contain monazite- Ce with significant Th substitution, uranoan thorite, zircon also showing extensive solid-solution toward thorite , and rare xenotime and pyrochlore. Biotite dehydration reactions have led to significant development of leucosome in the host pelitic gneisses, and likely resulted in the formation of granitic melt at depth.
Acta Geochimica (v.30, #2)
Search Acta Geochimica v. Marine strata are widely exposed in the Hushan and Chaohu areas, Lower Yangtze region. As biomarker geochemistry of the strata has not been well documented, this paper deals with the biomarker composition of representative samples collected from the Silurian, Carboniferous and Triassic systems and their geological implications, thus providing clues to marine organic matter.
On the basis of experimental results, it is shown that abundant biomarkers e. As organic matter in the strata is highly to over mature in general based on petrologic microobservation, some biomarkers mainly n-alkanes except terpanes and steranes cannot reflect the source, depositional environment and maturity of organic matter.
Thus, primarily based on analyses of the terpanes and steranes, it is suggested that organic matter in the Silurian and Carboniferous strata is derived mainly from lower organisms, while higher plants are predominant in the Triassic organic matter.
Pitchblende mineralization was studied in the younger granite samples collected from Gabal Gattar, north Eastern Desert, Egypt using electron scanning microscope (ESM) and electron probe microanalyses (EPMA). This study revealed that this pitchblende contains significant Zr content reaching up to (% ZrO2), which suggests that volcanic rocks were probably the source of such a deposit.
Received 7 January Although chemical non-isotopic UThPb dating of monazite by electron microprobe is well-established,hod is still controversial. Relatively U-rich zircon up to ppm of U from thest case for the technique. The isotopic systems used mostwidely for dating rocks with complex thermal histories include UPband ThPb,which occur in chemically robust accessoryminerals such aszircon ZrSiO4 and monazite REEPO4 that grow episodically inresponse to geological processes affecting the host rock e.
Determining theages of growth zones within crystals on amicrometre-scale analysis hasbecome commonplace since the development and increased availabilityof microanalytical methods utilizing ion SHRIMPe. Before monazite chemical dating became an established technique,common lead Pbc contamination could not be assessed. Chemical non-isotopic dating ofmonazite e.
Ages are calculated from total Th, U and Pb concentrations inmonazite, asmeasured in almost all cases by electronmicroprobe.
Analyses were stored as element concentrations in oxide-like compounds. Background effects were not compensated separately, being included in the standardization of the overlap correction factors. Analytical values of the spot data were recalculated as stoichiometric monazite for 8 cation charges corresponding to 4 oxygen atoms or used as element concentration for geochronology and chemical plots.
In order to quantitatively define the shape of the normalized plot, the following elemental ratios were calculated: For age calculation the element concentration are converted in numbers of atoms. The reason for deriving an explicit approximation of the age of the spot data is that, though ages can be precisely calculated from iteration of the implicit age equation, the corresponding errors can be rigorously propagated only through explicit expressions.
Kawakami, T. , Contrasting behaviour of monazite and zircon during partial melting and fluid infiltration: An example from the Ryoke metamorphic belt, Japan. Goldschmidt (Florence), Mineralogical Magazine, 77(5)
Electron Microprobe Dating of Monazite We are a research and service division of: No non-radiogenic lead in monazite or at least very little If you can precisely measure U, Th, and Pb in ppm , you can solve this equation iteratively for lead to obtain an age Map thin section with the microprobe Ce, Fe, Y to find all monazite crystals Map monazite grains Th, Y, U to see chemical domains Measure major elements for matrix corrections Spot analyses Measure: See an abstract of Williams et al.
This sample is currently used at UMass to test analytical precision. The outcrop it was taken from is part of a screen of supracrustal rocks intruded by the1. For further background information, see an abstract of Read et al. The probe data overall are consistent with the isotopic age, but with considerable variability see the data spreadsheet, and the grain maps and images for details. Data analysis download a Kb Excel file The probe data files have been organized into a spreadsheet modeled on the spreadsheet that Mike supplied that computes the ages.
Several improvements have been made: Error estimates analytical precision based on counting statistics have been automated. The standard error of the mean didn’t appear to work very well for these analyses because of ambiguity regarding mixed populations of ages in the sample monazites. The age is calculated using macros which iterate the age equations until a solution is reached to 0.
Be sure to read the comments on the macros by editing them you may need to configure Excel to use the ‘solver’ module. One macro iterates for one column of ages and should be used on the ‘All data’ sheet while the other iterates two columns of ages on the error sheets — e.
Prof. Dr. Bernhard Schulz
Electron microprobe analysis of monazite was carried on grains of various grade and setting. Major element and trace element contents as well as mapping were used to investigate effects of progressive metamorphism on chemical composition of monazite. Analyses of major elements were used to document chemical variation with metamorphic grade and mineral association.
Y is one the main elements of interest. Monazite composition shows an increasing concentration of Y from low grade to high grade with a significant jump at the sillimanite isograd. Other elements such as Th and REE also show variation depending on metamorphic grade or petrological setting.
Tomokazu Hokada. My portal; Neighbors. Kazuyuki Shiraishi 01/05, updated. U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand — A new report of Early Paleozoic granite. New SHRIMP U-Pb zircon ages and CHIME monazite ages from South Harris granulites, Lewisian.
New Zealand Journal of Geology and Geophysics, 45 2 , -. Precambrian Research, 87 , Australian Journal of Earth Sciences, 42 1 , Geology, 20 2 , Tectonophysics, 4 , Precambrian Research, 63 , Australian Journal of Earth Sciences, 49 1 , Precambrian Research, , Geologie En Mijnbouw, 74 1 , Indian Journal of Marine Sciences, 33 2 , Canadian Journal of Earth Sciences, 28 8 , Journal of the Geological Society of India, 42 3 , Island Arc, 9 1 , Journal of the Geological Society of India, 44 4 ,
Track Mounted Monazite
Tyrannosaurus rex lived in Late Cretaceous, but if you write: This text is inaccurate and irrelevant. Firstly, the name of eons and aeons, etc are derived by reference to the classical bostratigraphic nomenclature. For instance, the Proterozoic is the age before multi-cellular animals.
radiometric dating of single-grained detrital zircon/monazite was initiated through the CHIME method, which includes electron microprobe analyses and Th–U-total Pb isochron (e.g., Suzuki.
Thus, a negligible persistence in comparison with the integration time between two detector readings is achieved. Field of the Invention The present invention relates to an X-ray detecting apparatus, in particular, a detector for determining a type of material of an object, through which X-rays are passed.
Related Art To determine the type of material of an object through which X-rays are passed, there are known detector arrangements consisting of a plurality of detectors, mainly arranged in pairs. Each pair of detectors consists of two radiation detectors, which are arranged in succession and are penetrated in succession by X-ray quanta of a radiation source, with the front detector having a lower absorption than the rear detector, especially at higher energy levels; low energy X-ray quanta are absorbed almost completely in the low energy detector positioned in front.
Higher energy X-ray quanta pass through the low energy detector with almost no interaction and are absorbed in the high-energy detector at the rear. The front detector may have a lower thickness than the rear detector.
Current issues are now on the Chicago Journals website. Read the latest issue. One of the oldest journals in geology, The Journal of Geology JG has since promoted the systematic philosophical and fundamental study of geology. JG publishes original research across a broad range of subfields in geology, including geophysics, geochemistry, sedimentology, geomorphology, petrology, plate tectonics, volcanology, structural geology, mineralogy, and planetary sciences.
Many of its articles have wide appeal for geologists, present research of topical relevance, and offer new geological insights through the application of innovative approaches and methods. The “moving wall” represents the time period between the last issue available in JSTOR and the most recently published issue of a journal.
Th-U-total Pb monazite dating in mica schist was performed with the CAMECA SX electron microprobe using 20 kV accelerating voltage, nA beam current, and 1-μm beam diameter. Th, U and Pb were calibrated with M a, M b, and M a spectral lines .
Petrography of the Host Rock Pitchblende mineralization occurs in the younger granite of Gabal Gattar as vein-type. These younger granites are pink to reddish in color, massive and show few mafic minerals. This granite displays in some areas hematitic alteration especially in the fault zones. Microscopic studies revealed that the rock is medium to coarse-grained and essentially composed of quartz, perthite, potash feldspars with subordinate amount of plagioclase, biotite and secondary muscovite.
Accessory minerals are zircon, fluorite and some apatite. It is found in two generation, the older fills the interstices between the feldspar crystals, whereas the younger is graphically intergrowth with perthite crystals Figure 4 A. Perthite occurs as subhedral megacrysts up to 2. Perthitic veinlets are the most predominate type of perthite in these rocks Figure 4 A. Potash feldspare are mainly perthite with few amount of microcline and orthoclase crystals.
The orthoclase occurs as anhedral to subhedral crystals reaching 2.
U pb dating method
Representing diverse igneous and metamorphic lithologies, these grains yielded conventional isotopic ages ranging in age from Neoarchean to Devonian. Chemical dating was performed at Virginia Tech using a Cameca SX EMP in which the analytical routines and settings were specifically optimized for monazite geochronology, including correction of analytical peaks for all major spectral interferences and correction of peak intensities for local background emission.
Placement of cross-grain analytical traverses was based on backscattered electron BSE images together with wavelength-dispersive WD generated X-ray maps for Y, Th, U, and Ca, which revealed the internal compositional complexity of each grain. Analytical dates were either accepted or excluded based on analytical and spatial justifications. Isotopic dating techniques utilize three independent age calculations, provided the sample is old enough to have accumulated sufficient Pb i. Similarly, the chemical dating method can utilize two independent age calculations i.
CHIME dating and age mapping of monazite in granulites and paragneisses from the Hwacheon area, Korea: implications for correlations with Chinese cratons.
Show abstractHide abstract The crystal structure of iridescent garnet from Tenkawa village, Nara prefecture, Japan was investigated by means of Single—crystal X—ray diffraction method. The BSE image of the cross section shows very fine lamellae texture consisting of andradite—rich and grossular—rich layers. The average chemical composition was determined as Ca3.
Some reflections which violate the extinction rule for the space group Ia3d were observed and indicated that all glide planes are absent. Triclinic symmetry with the space group I1 should be suitable for the structure refinement. The iridescent garnet from Tenkawa shows very fine lamellae texture consisted of Fe—rich and Al—rich layers, therefore, the refined crystal structure of the Tenkawa garnet should be a superimposed structure of these chemically distinct layers.
The Fe—rich layer have almost pure andradite composition, so cation ordering in the Fe—rich layer is negligible. The Al—rich layer should have more obvious ordered cation distribution than the Fe—rich layer. The ordered cation distribution in the Al—rich layer should mainly contribute the cation ordering in the refined crystal structure of the Tenkawa garnet.
Structural Geology and Tectonics
Continental delamination and the Colorado Plateau. Journal of Geophysical Research, 84, — Th diffusion in monazite.
Bindu R. S., Suzuki K., Yoshida M. and Santosh M. () The first report of CHIME monazite age from the South Indian granulite terrane. Current Science, 74 (10), 古山勝彦・沢田順弘・板谷徹丸・三宅康幸（）近畿北部，鮮 新世照来層群寺田火山岩層の K-Ar 年代．地球科学，52,
Papers Conferences Journal of Mineralogical and Petrological Sciences , , Implications towards provenance, its shift and regional stratigraphic correlation. The Journal of the Geological Society of Japan, , Geological Society of India, 87, Journal of Geosciences, 61, Island Arc, 25, Journal of Mineralogical and Petrological Science, , Syntectonic granitic crust formation during back-arc rifting.
Earth and Planetary Science Letters, , Integrated isotopic ages and correlation of the basement plutonic rocks of the borehole Kukizaki core at southern Tsukuba City, Japan. The Journal of Geology, , Age of the Taishu Group, southwestern Japan, and implications for the origin and evolution of the Japan Sea.
Progress in the project – a fleeting summary
The shale is easily quarried into smooth blocks which can be readily placed in position. The blocks are compact and yet elast ic under changes of temperature, seem to possess sufficient strength, and are very resistant to weathering. As a buiiding material it is finely.
U/Pb-SHRIMP dating and Pb stepwise leaching (PbSL) experiments on zircons and garnets, respectively have confirmed the lack of Precambrian outcrops within the crystalline basement of Thailand.
Mechanics of Variscan Orogeny: A modern view on orogenic research. Growth-zoned garnets crystallized in gneisses and micaschists and display different Mg-Fe-Mn-Ca evolution trends in the metamorphic units. Microstructurally-controlled geothermobarometry based on cation exchange and net transfer reactions was used to reconstruct syndeformational prograde P-T paths. The P-T paths do not pass eclogite-facies conditions.
Different metamorphic peak temperatures confirm the individual character of the evolution in each of the units. Monazite ages compiled from numerous matrix grains range between and Ma in single samples. The inverted metamorphic stratigraphy can be explained by contractional crustal tectonics. In a southern domain, the nappe pile was overprinted by a second event with top-to-SE shearing at low pressures.