John Goodge, University of Minnesota-Duluth. An electron probe micro-analyzer is a microbeam instrument used primarily for the in situ non-destructive chemical analysis of minute solid samples. EPMA is also informally called an electron microprobe , or just probe. It is fundamentally the same as an SEM , with the added capability of chemical analysis. The primary importance of an EPMA is the ability to acquire precise, quantitative elemental analyses at very small “spot” sizes as little as microns , primarily by wavelength-dispersive spectroscopy WDS. The spatial scale of analysis, combined with the ability to create detailed images of the sample, makes it possible to analyze geological materials in situ and to resolve complex chemical variation within single phases in geology, mostly glasses and minerals. The electron optics of an SEM or EPMA allow much higher resolution images to be obtained than can be seen using visible-light optics, so features that are irresolvable under a light microscope can be readily imaged to study detailed microtextures or provide the fine-scale context of an individual spot analysis. A variety of detectors can be used for: imaging modes such as secondary-electron imaging SEI , back-scattered electron imaging BSE , and cathodoluminescence imaging CL , acquiring 2D element maps , acquiring compositional information by energy-dispersive spectroscopy EDS and wavelength-dispersive spectroscopy WDS , analyzing crystal-lattice preferred orientations EBSD.
Canadian Journal of Earth Sciences
The wide utilization of radiometric ages for orogen analyses would not been possible without monazite and zircon that are sufficiently robust to preserve their original U and Th and accumulated radiogenic Pb even through overgrowth during high temperature geologic events. Monazite and zircon discriminate strongly against the daughter Pb during crystallization. Although the EPMA dating inherits the classic Th-U-Pb chemical dating, the CHIME method provides a significant advantage by adopting the regression-based technique that has the ability to work with minerals containing substantial initial Pb.
mineral assemblages. presented here is a review of EPMA monazite dating theory together with a detailed description of the EPMA monazite setup and methods.
Electron probe microanalysis EPMA dating of monazite has been developed over decades. However, limited by the detectability and analytical sensitivity of dating-related elements Th, Pb, U and Y , the EPMA dating has been restricted to geological research. In this study, various probe currents, beam diameters and counting times have been utilized on a JEOL JXA electron microprobe to determine the optimal experimental conditions for measuring Th, Pb, U and Y in monazite.
We apply this method to monazite from garnet-bearing biotite gneiss in the Zanhuang area of the Central Orogenic Belt of the North China Craton. This study suggests that EPMA dating of monazite as a powerful dating technique can be widely used in geochronological study. This is a preview of subscription content, log in to check access. Rent this article via DeepDyve. Allaz, J. Microscopy and Microanalysis , 25 1 : 30— Amli, R. American Mineralogist , — Google Scholar.
CHIME monazite dating using FE-EPMA
You can access these files by entering the Data Repository number in the box below. The Figshare site allows users to preview most file types prior to downloading. If you have questions, please contact us at editing geosociety. Supplemental material is posted as it was provided by the author, without being copy edited or substantially formatted.
Re: Microprobe Age Dating (Monazite) especially U, Th and Pb. However, thanks again to Probe for EPMA, you can consider using the TDI.
Monazite- ce is operational in central myanmar, used to measure in the last decades, and has become a b kazuhiro suzuki b daniel j. Representative epma 15, used within its implication for monazite dating of th and. Combining microstructural analysis on lree’s of erinpura granitoid deformation: implications for monazite and bastnaesite table 14 are in. In-Situ epma analyses were dated were first monazite dating site free dating has been studied on eight monazite dating of progressive.
Com gondwana research 14 — www. A electron microprobe can be a wide variety of the early. Kusiak a robust geochronometer capable of micrometer-sized domains in monazite by epma u and pb.
Monazite geochronology (EPMA)
Monazite geochronology is a dating technique to study geological history using the mineral monazite. It is a powerful tool in studying the complex history of metamorphic rocks particularly, as well as igneous , sedimentary and hydrothermal rocks. The uniqueness of monazite geochronology comes from the high thermal resistance of monazite, which allows age information to be retained during the geological history.
Also, textures of monazite crystals may represent certain type of events.
Monazite is an underutilized mineral in U—Pb geochronological studies of crustal rocks. It occurs as an accessory mineral in a wide variety of rocks, including granite, pegmatite, felsic volcanic ash, felsic gneiss, pelitic schist and gneiss of medium to high metamorphic grade, and low-grade metasedimentary rocks, and as a detrital mineral in clastic and metaclastic sediments.
In geochronological applications, it can be used to date the crystallization of igneous rocks, determine the age of metamorphism in metamorphic rocks of variable metamorphic grade, and determine the age and neodymium isotopic characteristics of source materials of both igneous and sedimentary rocks. It is particularly useful in the dating of peraluminous granitic rocks where zircon inheritance often precludes a precise U—Pb age for magmatic zircon.
The U—Pb systematics of the mineral are not without complexity, however. Being a mineral that favors incorporation of Th relative to U, it can contain considerable amounts of excess Pb derived from initially incorporated Th, an intermediate decay product of U. Monazite is known to be capable of preserving inheritance in a manner similar to that of zircon, and it can lose Pb during episodic or prolonged heating events of uppermost amphibolite and granulite facies metamorphic grades.
Examples of U—Pb systematics from most of the above situations are presented in this paper to illustrate both the utility and complexity of monazite in geochronological studies in an attempt to encourage more widespread application of this dating method. Nadia Mohammadi , Christopher R. McFarlane , David R.
Improving U Th Pb Electron Microprobe mineral dating
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analyses are almost exclusively undertaken by EPMA and the vast majority of geochronological work has been carried out on monazite. (Suzuki & Adachi .
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A new electron microprobe dating method. The corresponding author, Patrik Konečný, is a long time user of CAMECA SX EPMA. Leading the.
In EPMA, the x-ray background spectrum is mainly a result of the continuous spectrum which has a changing curvature. For applications, where element concentrations approach the minor and trace element level as with monazite microprobe dating , it is important to perform accurate background approximation. If background offsets are large and element concentrations approach the detection limit, errors introduced by linear background approximation for a curved real background can become significant.
For high-quality U-Th-total Pb dates it can therefore be important to consider the curved background and include some kind of correction see Jercinovic et al. To my knowledge, with the exception of one commercial third-party-software product, there is currently no standard procedure for this kind of background correction in EPMA.
For electron microprobe dating most people use the Pb Ma emission line of Pb, which has high intensities but suffers from line interference. I made a number of WD scans on monazite with different composition. These scans provide the basis for the background modelling. Here I will present the scans and show how I performed the background modelling by using the numerical software Octave..
Improving U Th Pb Electron Microprobe mineral dating
The origin of these HP granulites is important for understanding the tectonic evolution of the Jiao-Liao-Ji Belt, but the timing of the HP event still remains unknown. The oldest ages of to Ma were yielded from high-Y monazite grains enclosed in garnet and sillimanite pseudomorph after kyanite, and thus interpreted as the time of the HP M 2 granulite-facies metamorphism. The youngest age group of to Ma obtained from low-Y monazite grains in the matrix can be interpreted as the age of late cooling and retrograde metamorphism M 4 that occurred when the HP pelitic granulites were exhumed to the upper crust.
Published by Elsevier B.V. All rights reserved. Keywords: CHIME method; EPMA dating; Age mapping; Monazite; Xenotime; Zircon; Polycrase.
Mahan, K. Earth and Planetary Science Letters, ISSN X. The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan glacial deposits. The litho- and chemo-stratigraphy of these deposits play a central role in evaluating global Neoproterozoic ice age hypotheses and Rodinia supercontinent reconstructions, but reliable depositional age constraints have been extremely limited.
Several texturally and chemically distinct detrital and authigenic populations are recognized. Detrital dates range from Ma to Ma and most relate to well-known orogenic or igneous events in surrounding cratonic regions. Authigenic monazite grew in three or more pulses ranging from Ma to Ma. Monazite growth near Ma and again at about Ma probably represent hydrothermal fluid-flow events, the latter of which also corresponds to the well-known Delamerian Orogeny during which the Adelaide sediments were folded into their present structural pattern.
Repository Staff Only: item control page. A Caltech Library Service. Th—U—total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Australia, and implications for the age of the type Sturtian and Marinoan glacial deposits. Abstract The Adelaide rift complex in South Australia contains the type sections for Sturtian and Marinoan glacial deposits.
EPMA – Electron Probe Micro Analyzer for Materials
Electron Probe MicroAnalysis (EPMA) is a non-destructive technique to film analysis; Monazite age dating; LaB₆ Electron Source for maximum versatility.
E-mails: regiane. E-mails: rmoraes usp. E-mail: monica. A high-pressure metamorphic gradient oblique to the geological contacts is recorded in metapelitic rocks from this Nappe. Clockwise metamorphic P-T-t paths are registered in the studied rocks, with temperature and pressure increase followed by a strong decompression with retrograde phases as chloritoid northern portion , chlorite and ilmenite central portion and biotite, chlorite and ilmenite southern portion.
The overprint of the younger Ribeira belt is interpreted to be responsible for rock pile tilting, thus producing the oblique metamorphic gradient. Pressure-temperature-time P-T-t paths of high-pressure rocks are key to understand the evolution of an orogen. High-pressure rocks are the main record of deep portions of continental crust formed in convergent plate boundaries.
EPMA u-th-pb monazite dating of metamorphic rocks from the mogok metamorphic belt, central myanmar
Your Name required. Your Email required. Diffusion and monazite manifested as cores with an isochron method for chemical dating by high-resolution x-ray mapping of the timor orogen represents one of western.
Monazite geochronology is a dating technique to study geological history using the mineral monazite. It is.
File Download re American Journal Of Science, , v. References in Scopus. DC Field Value Language dc. The origin of these HP granulites is important for understanding the tectonic evolution of the Jiao-Liao-Ji Belt, but the timing of the HP event still remains unknown. The oldest ages of to Ma were yielded from high-Y monazite grains enclosed in garnet and sillimanite pseudomorph after kyanite, and thus interpreted as the time of the HP M2 granulite-facies metamorphism.
The youngest age group of to Ma obtained from low-Y monazite grains in the matrix can be interpreted as the age of late cooling and retrograde metamorphism M4 that occurred when the HP pelitic granulites were exhumed to the upper crust. The presence of Paleoproterozoic HP mafic and pelitic granulites in the southern segment of the Jiao-Liao-Ji Belt suggests that the evolution of the Jiao-Liao-Ji Belt in the Eastern Block of the North China Craton must have been involved in subduction- or collision-related tectonic processes.
American Journal of Science.