Young asteroid mixing revealed in ordinary chondrites: The case of NWA 5764, a polymict LL breccia with L clasts

1Jérome Gattacceca,2,3Agata M. Krzesińska,4Yves Marrocchi,5Matthias M. M. Meier,6Michèle Bourot-Denise,7Rob Lenssen
Meteoritics & Planetary Science (in Press) Link top Article [DOI: 10.1111/maps.12942]
1CNRS, Aix-Marseille Univ, IRD, Coll France, CEREGE, Aix-en-Provence, France
2Department of Earth Sciences, Natural History Museum, London, UK
3Institute of Geological Sciences, Polish Academy of Sciences, Wrocław, Poland
4CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-les-Nancy, France
5ETH Zurich, Institute of Geochemistry and Petrology, Zurich, Switzerland
6IMPMC, MNHN, UPMC, UMR CNRS 7590, Paris, France
7Private meteorite collector, The Netherlands
Published by agreement with John Wiley & Sons

Polymict chondritic breccias—rocks composed of fragments originating from different chondritic parent bodies—are of particular interest because they give insights into the mixing of asteroids in the main asteroid belt (occurrence, encounter velocity, transfer time). We describe Northwest Africa (NWA) 5764, a brecciated LL6 chondrite that contains a >16 cm3 L4 clast. The L clast was incorporated in the breccia through a nondestructive, low-velocity impact. Identical cosmic-ray exposure ages of the L clast and the LL host (36.6 ± 5.8 Myr), suggest a short transfer time of the L meteoroid to the LL parent body of 0.1 ± 8.1 Myr, if that meteoroid was no larger than a few meters. NWA 5764 (together with St. Mesmin, Dimmitt, and Glanerbrug) shows that effective mixing is possible between ordinary chondrite parent bodies. In NWA 5764 this mixing occurred after the peak of thermal metamorphism on the LL parent body, i.e., at least several tens of Myr after the formation of the solar system. The U,Th-He ages of the L clast and LL host, identical at about 2.9 Ga, might date the final assembly of the breccia, indicating relatively young mixing in the main asteroid belt as previously evidenced in St. Mesmin.

Discuss

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s