Electron Microprobe Dating of Monazite
U-Th-total Pb dating of monazite from orthogneisses and their ultra-high temperature metapelitic enclaves: implications for the multistage.
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. Therefore, direct sampling techniques with high spatial resolution are required, in order to study these tiny zones individually, without damaging the textures and zonations. The advantage of monazite geochronology is the ability to relate monazite compositions with geological processes. Finding the ages of compositional zones can mean finding the ages of geological processes.
Monazite is a rare-earth-element phosphate mineral , with the chemical formula e. It appears in a small amount as an accessory mineral in many igneous, metamorphic and sedimentary rocks. These two elements are what make this mineral suitable for radiometric dating. In the radioactive processes, the three unstable parent isotopes decay into their respective stable daughter isotopes of Pb. Each following a decay chain consisting of alpha and beta decays , parent isotopes U, U and Th, decay into a series of intermediate daughter isotopes, and finally lead to stable isotopes, Pb, Pb and Pb, respectively.
Each decay chain has a unique half-life , which means the daughter isotopes are generated at different rates. The decay processes can be simplified as the following equations, which omit all the intermediate daughter isotopes.
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Canadian Journal of Earth Sciences
Farley, Kenneth A. Reviews in Mineralogy and Geochemistry. ISBN Full text is not posted in this repository.
Chemical Th-U-total Pb method of dating monazite by an Electron Probe Micro Analyzer (EPMA) is a well-known technique for constraining chronology of.
The Acaiaca Complex AC is located in southeastern Minas Gerais state, and comprises felsic, mafic, ultramafic, and aluminous granulites as well as lower grade gneisses and mylonites. The complex is distributed over an area of ca. The discrepancy in the metamorphic grade between both complexes led to the present study aiming to understand the metamorphic history of the AC by means of geothermobarometric calculations and electron microprobe Th-U-Pb monazite dating.
Part of the granulites was affected by anatexis. The melting of felsic granulites resulted in the generation of pegmatites and two aluminous lithotypes. These are:. Th-U-Pb monazite geochronology of two granulite samples resulted in a metamorphic age around Ma, which is similar to the age of the MC registered in the literature. The similar Paleoproterozoic metamorphic ages of both complexes lead to the conclusion that the Acaiaca Complex may be the high grade metamorphic unit geochronologically related to the lower grade Mantiqueira Complex.
The granulites of the AC are distributed along a narrow strip within the amphibolite facies gneisses of the Mantiqueira Complex. This strip Figure 1 extends for at least 36 km in the north-south direction and has a width of about 6 km. Lithotypes derived from sedimentary protoliths have not been described for the Mantiqueira Complex in the region. Metamorphic ages of to Ma were obtained by Noce et al. The discrepancy in metamorphic grades between the Acaiaca and the Mantiqueira complexes, and the existence of lithotypes derived from sedimentary protoliths in the AC, led to the present study aiming to understand the metamorphic evolution of the AC.
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Colin A. Shaw, Karl E. Karlstrom, Michael L. Williams, Michael J. Jercinovic, Annie M. McCoy; Electron-microprobe monazite dating of ca.
Evaluation of Uncertainties in Dating of Monazite by Electron Microprobe. (PMID:). Abstract; Citations List of citations in Europe PMC which this record.
Monazite rim formation was facilitated via dissolution—reprecipitation of Neoproterozoic monazite. The monazite rims record garnet growth as they are depleted in Y 2 O 3 with respect to the Neoproterozoic cores. Rims are also characterized by relatively high SrO with respect to the cores. Results of the zircon depth-profiling revealed igneous zircon cores with crystallization ages typical for SNC metasediments. These results show that both monazite and zircon experienced dissolution—reprecipitation under high-pressure conditions.
Caledonian monazite formed coeval with garnet growth during subduction of the Vaimok Lens, whereas zircon rim formation coincided with monazite breakdown to apatite, allanite and clinozoisite during initial exhumation. To understand the subduction—exhumation dynamics of continental lithosphere that reached ultra- high pressure [ U HP] depths, we must extract information regarding the timing and conditions of prograde, peak and retrograde metamorphism.
Monazite rim formation was facilitated via dissolution-reprecipitation of Neoproterozoic monazite. The monazite rims record garnet growth as they are depleted in Y2O3 with respect to the Neoproterozoic cores. Rims are also characterized by relatively high SrO with respect to the cores. Results of the zircon depth-profiling revealed igneous zircon cores with crystallization ages typical for SNC metasediments.
These results show that both monazite and zircon experienced dissolution-reprecipitation under high-pressure conditions. Caledonian monazite formed coeval with garnet growth during subduction of the Vaimok Lens, whereas zircon rim formation coincided with monazite breakdown to apatite, allanite and clinozoisite during initial exhumation.
axis (FIA) controlled monazite dating of foliations in porphyroblasts and matrix showing enlargement of monazite grain (B) in location marked in boxed area.
Geological Survey Distributor : U. Toggle navigation ScienceBase-Catalog. Your browser does not have support for cookies enabled. Some features of this application will not work. Publication Date Time Period Moscati, R. Samples in the form of mounted loose grains were prepared and analyzed for direct age dating on a laser ablation inductively coupled plasma mass spectrometer LA-ICPMS system at the U.
Geological Survey in Denver, Colorado in February
(U-Th)/He Dating of Phosphates: Apatite, Monazite, and Xenotime
Petrology and monazite dating of the Fe-rich gneisses from Kokava Veporic Unit, Western Carpathians, Slovakia : Devonian sediments supplied from Gondwanan-sources metamorphosed in the Variscan times. Journal of Geosciences, volume 56 , issue 2 , – Geol Carpath Geol Zbor Geol Carpath Eclogae Geol Helv Int J Earth Sci
Prolonged Acadian orogenesis: Revelations from foliation intersection axis (FIA) controlled monazite dating of foliations in porphyroblasts and matrix.
Molten element ark. If there seem to be no signs of damage and the element continues to spark even when plugged into a different socket on the stove, it is most likely defective and should be replaced. A there is NOT a chemical reaction B there is a change at the molecular level C atoms are spread apart D electrical charges are involved Rare Earth Element Production: This chart shows a history of rare earth element production, in metric tons of rare earth oxide equivalent, between and A rock is an aggregate of one or more minerals, or a body of undifferentiated Shop a wide selection of Fishing Gear in the Amazon.
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Investigation of the monazite chemical dating technique
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Representing diverse igneous and metamorphic lithologies, these grains yielded conventional isotopic ages ranging in age from Neoarchean to Devonian. Save to Library. Create Alert. Launch Research Feed.
U–Th–Pb dating of monazite with the electron probe microanalyser (EPMA) is increasingly documented as a reliable geochronological method.
Polygenetic monazite grains in diverse Precambrian crystalline rocks from the Black Hills, South Dakota, have been analyzed in situ by ion and electron microprobe methods SHRIMP and EMP , to evaluate the accuracy and precision of EMP ages determined using a new analytical protocol that incorporates improved background acquisition and interference corrections. The monazite data set includes EMP chemical analyses from 26 grains in six metamorphic rocks, which resolve into 54 age-composition domains, and 31 SHRIMP isotopic ages from 13 grains in one of the rocks, with six grains microanalyzed in common by the two methods.
The data set also includes monazite-bearing garnets in two of the rocks, whose isotopic compositions were analyzed using Pb stepwise-leaching PbSL methods. The EMP data set is interpreted geologically as reflecting multiple episodes of monazite growth that are provisionally related to known metamorphic events in the Black Hills. Open Access.
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Chemical U-Th-Pb dating of monazite by 3D-Micro x-ray fluorescence analysis with synchrotron radiation. / Schmitz, Susanne; Möller, Andreas; Wilke, Max;.
Monazite is a light rare earth element LREE -bearing phosphate mineral. Crystals typically contain distinct chemical domains, each of which represent successive growth thru geologic history. Electron microprobe analysis can characterize the geometry and U-Th- total Pb age for each domain. This kind of data allow the growth of monazite to be related to geologic events affecting the host rock.
Monazite is common in pelitic and psammitic metamorphic rocks at greenschist facies and above where it is often recognized as inclusions in porphyroblasts but may also be in direct connection with the matrix. Locating monazite grains can be done on standard geological thin sections via x-ray compositional mapping. Figure 7A reveals a cerium x-ray map on a quartzite sample from the Cheyenne belt. Peaks in cerium content may correlate to large monazite grains.
Figure 8 shows compositional zonation on selected grains identified in figure 7. These individual domains likely represent successive generations of monazite growth and can be targeted for crystallization dates. Dating monazite follows the U-Th total Pb age method which is described elsewhere in the website. I will not discuss the specifics of this system but I have included the equation from which an age is determined:.