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Définition d’une collection de minéraux de référence afin de développer et de calibrer une méthode de datation in-situ adaptée à la surface de Mars

Abstract : Absolute age determination is necessary to check and calibrate the relative Martian chronology presently available from meteoritic crater counting. For this purpose, we have developed an in-situ K-Ar dating prototype for planetary surfaces at GEOPS laboratory. This instrument, supported by a CNES-CNRS research program, is a laser ablation-based system built to vaporize a reproducible volume of rock or mineral. It quantifies potassium content (K) by laser-induced breakdown spectroscopy (LIBS) and argon (Ar) by quadrupole mass spectrometry (QMS). The K-Ar age determination also requires accurate quantification of the ablated sample mass. Following an important period of experimental set-up development to improve precision, accuracy and sensitivity of the technique, our efforts focused on the calibration of the different parts of this instrument. To that purpose, a collection of reference samples (micas, feldspars, amphibolite, basalts) was done and analyzed (total chemistry and age measurements by K-Ar and ⁴⁰Ar/³⁹Ar conventional techniques). These samples show a K content between 0,15 and 11% and an Ar content between 1 and 100x10¹⁴ ⁴⁰Ar* atoms per gram, corresponding to Martian basalt from 700 Ma to 3 Ga for 0.4% K. The results obtained evidence a correlation between the ablation time and the ablated mass depending on the mineral phase analyzed. In order to check this correlation, measurements were conducted on several samples, in particular a microlitic basalt (Viluy basalt) similar to Martian basalts. The K-Ar in-situ age of 401 ± 41 Ma obtained by our approach is consistent with the age of 381 ± 5 Ma measured indepedently on mineral populations. More generally, this study allows to obtain K-Ar ages measured by our in-situ dating method with uncertainties lower than 15%, on relatively low-K and young samples compared to Martian rocks.
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Submitted on : Wednesday, March 7, 2018 - 2:36:09 PM
Last modification on : Wednesday, October 14, 2020 - 4:00:41 AM
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Fanny Cattani. Définition d’une collection de minéraux de référence afin de développer et de calibrer une méthode de datation in-situ adaptée à la surface de Mars. Instrumentation et méthodes pour l'astrophysique [astro-ph.IM]. Université Paris Saclay (COmUE), 2018. Français. ⟨NNT : 2018SACLS002⟩. ⟨tel-01725426⟩

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