Antarctic polymict eucrite Yamato 792769 and the cratering record on the HED parent body

• Main Authors: Bogard, D., Nyquist, L., Takeda, H., Mori, H., Aoyama, T., Bansal, B., Wiesemann, H., Shih, C.-Y.
• Format: Other/Unknown Material
• Language: unknown
• Published: 1993
• Subjects: 91; Antarctic; The Antarctic; Yamato; Antarc*
• Online Access: http://ntrs.nasa.gov/search.jsp?R=19930056652

Compared to most other Yamato polymict eucrites, Yamato Y792769 eucrite includes fewer and smaller eucritic clasts with homogenized pyroxenes, and its fine-grained matrix is shock-compacted and sintered. In this work, the relationships between the Antarctic eucrite Y792769, monomict eucrites, polymict eucrites, and isotopic ages are investigated, using results of Ar-39/Ar-40 method to date the time of the major thermal event on the Y792769 body and the Rb-Sr and Sm-Nd methods to determine whether relict older ages might have been preserved in some of the breccia materials. The Ar-39/Ar-40 time of the last thermal event which produced the Y792769 texture is 3.99 +/- 0.04 Ga. The complete resetting of the Ar-39/Ar-40 age is consistent with the texture of Y792769 observed in TEM, suggesting that shock compaction converted part of the matrix plagioclase to maskelynite. The Sm-Nd data give an age of 4.23 +/- 0.12 Ga, reflecting partial resetting of the Sm-Nd system during breccia formation. The 3.9 Ga Ar-39/Ar-40 age probably reflects a period of intense meteoroid bompardment which affected the entire inner solar system.