ANR-JC MONA

This project is funded by one ANR-JC grant (Mona, 2012). The project started in november 2012 with the recruitment of Alexis Grand’Homme, as PhD student co-supervised with Anne-Magali Seydoux-Guillaume (GET, Toulouse). This project requires a large panel of analytical facilities available in ISTerre, GET, or in other institutes. It implies therefore numerous collaborations in France and other international institutes.

***Aims and context

The aim of this project is to investigate the potential of monazite as chronometer and geochemical tracer of fluid mineralization via detailed characterization of natural samples and hydrothermal experiments.

***Abstract

Dating hydrothermal mineralization is challenging because most chronometers are commonly reset in open system. Although monazite is rare in hydrothermal deposits, it is very attractive to date mineralization because it has a very robust isotopic system (U-Th-Pb) that retains the age of its precipitation. In presence of successive fluid circulations, monazite (re)crystallizes sporadically. Growth episodes are identifiable from zoning in trace elements composition (REE+Y, Th, U and Pb). Using in-situ high resolution techniques (spot size 5µm), it is possible to date these distinct domains and to obtain the age of the successive mineralization stages. In monazite taken from Alpine clefts (Central Alps), preliminary SIMS U-Th-Pb dating gave very promising results. Results show that Miocene monazite can be dated with a resolution of 0.2 Ma. Within a single grain, it is possible to distinguish episodic growth stages separated by an interval <2Ma. Furthermore, monazite is zoned with extreme trace elements fractionation (Th/U up to 600), which remains to be understood.

The aim of this project is to investigate the potential of monazite as chronometer and geochemical tracer of fluid mineralization via detailed characterization of natural samples and hydrothermal experiments. The objectives are two-fold : (1) Obtaining monazite growth ages and growth duration for different areas of the Alps and to link them with the local deformation and exhumation history, (2) trying to understand chemical and isotopic behaviour of the REE+Y, Th, U and Pb during monazite/fluid interaction.

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Related papers and conference abstract}}}

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2014

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Papers
Janots E., Rubatto D., (2014). U-Th-Pb dating of collision in the external Alpine domains (Urseren zone, Switzerland) using low temperature allanite and monazite. Lithos, 184-187, 155-166

Conference Abstracts
Emilie Janots, Edwin Gnos, Alfons Berger, and Martin Whitehouse ; High spatial resolution dating of hydrothermal monazite from Alpine clefts ; EGU 2014

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2013

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Papers

  1. Berger A., Gnos E., Janots E., Whitehouse M., Soom M., Frei R., Waight T. E., (2013). Dating brittle tectonic movements with cleft monazite : Fluid-rock interaction and formation of REE minerals. Tectonics, Vol. 321176–1189
  2. De Ascenção guedes R., Meisser N., Janots E., Grand’homme A.*, de Parseval P. et Schaub L. (2013).Thorite, dessauite-(Y), hingganite-(Y) et monazite-(Ce) au Mont-Cenis, Lanslebourg, Savoie. Le Règne Minéral 112
  3. Gnos E., Janots E., Berger A. (2013) Quand les petits deviennent les stars : la monazite. Le cristallier Suisse 2/2013

[*

2012

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Papers
Janots E., Berger A., Gnos E., Whitehouse M., Lewin E., Pettke T. (2012). Constraints on fluid evolution during metamorphism from U–Th–Pb systematics in Alpine hydrothermal monazite Chemical Geology 326–327, 61-71