Dubious Radiogenic Pb Places U-Th-Pb Mineral Dating in Doubt

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.

Canadian Journal of Earth Sciences

Symposium on Geol. Resources of Madagascar – A good example of the usefulness of the in-situ dating method. Madagascar displays a huge portion of the lower crust and its study is fundamental for the understanding of the evolution of this part of the crust. Unfortunately, our knowledge of this domain is limited. At this time, numerous works structural, geochemical, petrological are in progress in Madagascar, but there are only a few geochronological data.

E-PROBE MONAZITE DATING IN MADAGASCAR: A good example of the usefulness of the in-situ dating method. C. NICOLLET, JM MONTEL, S. FORET.

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. Share This Paper.

Investigation of the monazite chemical dating technique

Research article 03 Apr Correspondence : Emmanuelle Ricchi emmanuelle. Thorium—lead Th-Pb crystallization ages of hydrothermal monazites from the western, central and eastern Tauern Window provide new insights into Cenozoic tectonic evolution of the Tauern metamorphic dome. Growth domain crystallization ages range from Fissure monazite ages largely overlap with zircon and apatite fission track data.

Besides tracking the thermal evolution of the Tauern dome, monazite dates reflect episodic tectonic movement along major shear zones that took place during the formation of the dome.

Numerous techniques have been published for dating monazite including isotope dilution measurements using thermal ionization mass.

Hacker, M. Racek, R. Holder, A. Kylander-Clark, K. Schulmann, P. Monazite laser ablation—split-stream inductively coupled plasma—mass spectrometry LASS was used to date monazite in situ in Barrovian-type micaschists of the Moravian zone in the Thaya window, Bohemian Massif. Heterogeneously developed retrograde shear zones S 3 are marked by widespread chloritization, but minor chlorite is present in the studied samples. Monazite is zoned, showing embayments and sharp boundaries between zones, with low Y in the staurolite zone, high-Y cores and low-Y rims in the kyanite zone, and high-Y cores, a low-Y mantle and a high-Y rim in the sillimanite zone.

A systematic increase in heavy rare earth element HREE content with decreasing monazite age from to Ma is correlated with growth on the prograde P—T path; the drop in HREE of monazite at — Ma is assigned to recrystallization. The presence of chlorite even in the least retrogressed samples witnesses limited external fluid availability on the retrograde P—T path. Migration of this fluid was probably responsible for heterogeneous fluid-assisted recrystallization and resetting of original prograde monazite, even where included in garnet, staurolite or kyanite.

The timing of burial in the Thaya window, a deformed part of the underthrust Brunia microcontinent, was coeval with exhumation of granulites and migmatites of the Moldanubian orogenic root at c. Monazite is extensively used to date metamorphism in medium-grade felsic rocks.

Geochronology

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.

Accessing Earth’s history using isotopic dating methods rocks, such as zircons and monazites, and is used to date materials up to billion years old.

Geochronology is the science of providing ages of events in the history of the Earth and extraterrestrial material and of determining the temporal rates of geological processes by using a number of different dating methods. The ages can be absolute e. Most absolute dating methods rely on the analysis of radioactive isotopes and their radiogenic decay products. A number of radioactive isotopes from different elements, such as uranium, thorium, rhenium, samarium, lutetium, rubidium and potassium are used for this purpose.

Techniques exist to date practically all geological materials, from billions of years in age to historical records. For instance:. From the large number of different geochronological methods we are currently apply the following:. Show navigation.

Electron Microprobe Dating of Monazite

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Thorium to uranium ratios in zircon, monazite, and xenotime.______. 10 geologically well dated rocks in order to test the validity of the method by use.

Geochronology involves understanding time in relation to geological events and processes. Geochronological investigations examine rocks, minerals, fossils and sediments. Absolute and relative dating approaches complement each other. Relative age determinations involve paleomagnetism and stable isotope ratio calculations, as well as stratigraphy. Speak to a specialist.

Geoscientists can learn about the absolute timing of geological events as well as rates of geological processes using radioisotopic dating methods. These methods rely on the known rate of natural decay of a radioactive parent nuclide into a radiogenic daughter nuclide. Over time, the daughter nuclide accumulates in certain minerals. Different isotopic systems can be used to date a range of geological materials from a few million to billions of years old.

The U- Th -Pb technique measures the amount of accumulated Pb, Pb and Pb relative to the amount of their remaining uranium and thorium parents in a mineral or rock. This technique is commonly applied to minerals from igneous, metamorphic and sedimentary rocks, such as zircons and monazites, and is used to date materials up to 4. The U-series technique uses the short half-lives of uranium and thorium isotopes to date geologically young material, such as fossils, speleothems, carbonates and volcanic rocks.

This dating technique is applied to samples of just a few years, up to about , years old. The K-Ar dating technique is based on measurement of the product of the radioactive decay of an isotope of potassium K into argon Ar and is used for samples a few thousand years and older such as igneous, volcanic and metamorphic rocks.

Improving U Th Pb Electron Microprobe mineral dating

Continue to access RSC content when you are not at your institution. Follow our step-by-step guide. We analysed standard zircon crystals using a zircon crystal Thompson Mine and Monangotory standard monazites, dated using a monazite crystal

A new electron microprobe dating method. he has been involved in the development of innovative dating methods for monazite, uraninite.

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Clicking on the donut icon will load a page at altmetric. Find more information on the Altmetric Attention Score and how the score is calculated. The U—Pb geochronologic analysis of accessory minerals has played an important role in Earth and solar system science in constraining the ages of a wide variety of rocks and minerals. Currently, the significant matrix effects observed between different accessory minerals and the lack of high-quality standards for many minerals of interest are the major limitations of its geochronological applications.

In this study, we investigated the effects of the addition of oxygen, nitrogen, and water vapor before and after the ablation cell on the accuracy of the U—Pb dating of different minerals e. We found that the addition of water vapor, unlike that of oxygen and nitrogen, before the ablation cell can significantly suppress the matrix effects on U—Pb dating.

This can be attributed to the suppression of elemental fractionation in both the laser ablation and ICP ionization processes by the presence of water vapor. The American Chemical Society holds a copyright ownership interest in any copyrightable Supporting Information. Files available from the ACS website may be downloaded for personal use only.

Absolute dating methods (ANT)