USRA Houston Repository

40Ar/39Ar ages of L4, H5, EL6, and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008 TC3)

Show simple item record

dc.contributor.author Goodrich, Cyrena Anne
dc.contributor.author Turrin, Brent D.
dc.contributor.author Lindsay, Fara
dc.contributor.author Delaney, Jeremy S.
dc.contributor.author Park, Jisun
dc.contributor.author Herzog, Gregory F.
dc.contributor.author Swisher Jr, Carl
dc.date.accessioned 2023-03-30T20:19:06Z
dc.date.available 2023-03-30T20:19:06Z
dc.date.issued 2023-02-22
dc.identifier.other DOI: https://doi.org/10.1111/maps.13953
dc.identifier.uri https://hdl.handle.net/20.500.11753/1847
dc.description.abstract The Almahata Sitta (AhS) meteorite consists of disaggregated clasts from the impact of the polymict asteroid 2008 TC3, including ureilitic (70%–80%) and diverse non-ureilitic materials. We determined the 40Ar/39Ar release patterns for 16 AhS samples (3–1500 μg) taken from three chondritic clasts, AhS 100 (L4), AhS 25 (H5), and MS-D (EL6), as well as a clast of ureilitic trachyandesite MS-MU-011, also known as ALM-A, which is probably a sample of the crust of the ureilite parent body (UPB). Based on our analyses, best estimates of the 40Ar/39Ar ages (Ma) of the chondritic clasts are 4535 ± 10 (L4), 4537–4555 with a younger age preferred (H5), and 4513 ± 17 (EL6). The ages for the L4 and the H5 clasts are older than the most published 40Ar/39Ar ages for L4 and H5 meteorites, respectively. The age for the EL6 clast is typical of older EL6 chondrites. These ages indicate times of argon closure ranging up to 50 Ma after the main constituents of the host breccia, that is, the ureilitic components of AhS, reached the >800°C blocking temperatures of pyroxene and olivine thermometers. We suggest that these ages record the times at which the clasts cooled to the Ar closure temperatures on their respective parent bodies. This interpretation is consistent with the recent proposal that the majority of xenolithic materials in polymict ureilites were implanted into regolith 40–60 Ma after calcium–aluminum-rich inclusion and is consistent with the interpretation that 2008 TC3 was a polymict ureilite. With allowance for its 10-Ma uncertainty, the 4549-Ma 40Ar/39Ar age of ALM-A is consistent with closure within a few Ma of the time recorded by its Pb/Pb age either on the UPB or as part of a rapidly cooling fragment. Plots of age versus cumulative 39Ar release for 10 of 15 samples with ≥5 heating steps indicate minor losses of 40Ar over the last 4.5 Ga. The other five such samples lost some 40Ar at estimated times no earlier than 3800–4500 Ma bp. Clustering of ages in the low-temperature data for these five samples suggests that an impact caused localized heating of the AhS progenitor ~2.7 Ga ago. In agreement with the published work, 10 estimates of cosmic-ray exposure ages based on 38Ar concentrations average 17 ± 5 Ma but may include some early irradiation.
dc.format.mimetype application/pdf
dc.language.iso en en
dc.publisher Meteoritics & Planetary Science en
dc.relation.ispartofseries LPI contribution ; no. 2884
dc.subject.lcsh Achondrites
dc.title 40Ar/39Ar ages of L4, H5, EL6, and feldspathic ureilitic clasts from the Almahata Sitta polymict ureilite (asteroid 2008 TC3) en
dc.type Article en
dc.rights.license This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License,


Files in this item

This item appears in the following Collection(s)

  • LPI Contributions
    Documents the scientific research, meetings, and outreach products from the LPI.

Show simple item record

Search HOU Repository


Browse

My Account