Publications by authors named "Jean Bollard"

3 Publications

  • Page 1 of 1

Volatile element evolution of chondrules through time.

Proc Natl Acad Sci U S A 2018 08 6;115(34):8547-8552. Epub 2018 Aug 6.

Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, CNRS UMR 7154, 75238 Paris Cedex 05, France.

Chondrites and their main components, chondrules, are our guides into the evolution of the Solar System. Investigating the history of chondrules, including their volatile element history and the prevailing conditions of their formation, has implications not only for the understanding of chondrule formation and evolution but for that of larger bodies such as the terrestrial planets. Here we have determined the bulk chemical composition-rare earth, refractory, main group, and volatile element contents-of a suite of chondrules previously dated using the Pb-Pb system. The volatile element contents of chondrules increase with time from ∼1 My after Solar System formation, likely the result of mixing with a volatile-enriched component during chondrule recycling. Variations in the Mn/Na ratios signify changes in redox conditions over time, suggestive of decoupled oxygen and volatile element fugacities, and indicating a decrease in oxygen fugacity and a relative increase in the fugacities of in-fluxing volatiles with time. Within the context of terrestrial planet formation via pebble accretion, these observations corroborate the early formation of Mars under relatively oxidizing conditions and the protracted growth of Earth under more reducing conditions, and further suggest that water and volatile elements in the inner Solar System may not have arrived pairwise.
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http://dx.doi.org/10.1073/pnas.1807263115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6112700PMC
August 2018

Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules.

Sci Adv 2017 08 9;3(8):e1700407. Epub 2017 Aug 9.

Centre for Star and Planet Formation, University of Copenhagen, Copenhagen, Denmark.

The most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. Using Pb-Pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after the formation of the Sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. This finding is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. An abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion.
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http://dx.doi.org/10.1126/sciadv.1700407DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5550225PMC
August 2017

Pb-Pb dating of individual chondrules from the CB chondrite Gujba: Assessment of the impact plume formation model.

Meteorit Planet Sci 2015 Jul;50(7):1197-1216

Centre for Star and Planet Formation, Natural History Museum of Denmark, DK-1350 Copenhagen, Denmark.

The CB chondrites are metal-rich meteorites with characteristics that sharply distinguish them from other chondrite groups. Their unusual chemical and petrologic features and a young formation age of bulk chondrules dated from the CB chondrite Gujba are interpreted to reflect a single-stage impact origin. Here, we report high-precision internal isochrons for four individual chondrules of the Gujba chondrite to probe the formation history of CB chondrites and evaluate the concordancy of relevant short-lived radionuclide chronometers. All four chondrules define a brief formation interval with a weighted mean age of 4562.49 ± 0.21 Myr, consistent with its origin from the vapor-melt impact plume generated by colliding planetesimals. Formation in a debris disk mostly devoid of nebular gas and dust sets an upper limit for the solar protoplanetary disk lifetime at 4.8 ± 0.3 Myr. Finally, given the well-behaved Pb-Pb systematics of all four chondrules, a precise formation age and the concordancy of the Mn-Cr, Hf-W, and I-Xe short-lived radionuclide relative chronometers, we propose that Gujba may serve as a suitable time anchor for these systems.
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http://dx.doi.org/10.1111/maps.12461DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4946626PMC
July 2015