20-EPN-034: Calibration of the Al-in-olivine thermometer: Insight into the thermal history of type II chondrules

20-EPN-034: Calibration of the Al-in-olivine thermometer: Insight into the thermal history of type II chondrules

Visit by Thomas van Gerve and Kat Shepherd, KU Leuven (Belgium) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 18-22 October 2021

Report Summary:

Chondrites are the most primitive agglomerates formed in the solar system. In this project, we want to develop a thermometer based on Al-in-olivine/spinel equilibrium to calculate the temperature of formation of chondrites. or this project, we have performed a large number of new low- to high-pressure (1 atm – 10 GPa) experiments relevant to chondrule formation at the KU Leuven.

Experiments were run at high temperature (1200-1800°C), under variable oxygen fugacity conditions (IW+1 to IW+5, IW = iron-wustite). From 18-22 October 2021, Thomas van Gerve and Kat Shepherd (KU Leuven) worked with the Cameca IMS 1270 E7 ion probe at CRPG, Nancy, under the supervision of Dr. Johan Villeneuve and M. Nordine Bouden. We have measured the following masses: 12C, 16O1H, 18O, 19F, 27Al, 30Si, 32S and 35Cl in olivine, glass and glass inclusions. During our analytical session, we measured ~ 150 points in olivine and glass in addition to the standards. Results are extremely reproducible and show a trend of slightly increasing Al content in olivine as a function of the Fo content (molar Mg/(Mg+Fe)) of olivine. Using our new SIMS results, we are in the process of developing a thermodynamically rooted model taking into account major components in spinel and olivine.

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20-EPN-050: 26-Aluminium-26-Magnesium systematics of chondrules and clasts in unequilibriated ordinary chondrites

20-EPN-050: 26-Aluminium-26-Magnesium systematics of chondrules and clasts in unequilibriated ordinary chondrites

In-person visit by Audrey Bouvier (Universität Bayreuth, Germany) to TA2.9 Ion probe facility (IPF), CRPG (France).
Dates of visit: 7-11 June 2021

Chondrules are a major component of chondritic meteorites whose time and mechanism of formation are still debated. Inconsistencies in formation ages of chondrules have been found between ages determined by the absolute Pb-Pb chronometer or using the relative 26Al-26Mg chronometer. While the Pb-Pb ages suggest that chondrules formed continuously for about 4 Ma from the time of CAI formation, the 26Al-26Mg data show evidence that chondrules did not form until about 1.8 Ma after CAIs. One possible explanation could be a heterogeneous distribution of 26Al in the solar nebula.

To evaluate this hypothesis, we used secondary ionization mass spectrometry (SIMS) to date chondrules and clasts from unequilibrated ordinary chondrites with the 26Al-26Mg chronometer. Three chondrules from ordinary chondrites show resolvable excesses in 26Mg due to the decay of 26Al and formed around 2 Ma after CAI formation, consistent with previous studies. Analysis of a large igneous inclusion from Paposo 004 supports a formation age within 1 Ma after CAI. The presence of a relict olivine chondrule in this inclusion provides contextual evidence that chondrule formation must have taken place prior to this time.


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