On the thermal history of heavily shocked Yanzhuang H‐chondrite

Abstract

Abstract Partly shock‐melted Yanzhuang H‐chondrite, now classified as petrological type H6 but before the shock event of type H4, was subjected to the shock‐heating 2.6 Ma ago at the time it was spalled off its parent body and came into being as a meteoroid of ca. 30 cm radius. At that time the unmelted portion of the meteoroid suffered an almost complete loss of its radiogenic 4He and 40Ar while the contents of the most volatile non‐noble gas elements Zn and Se were not measurably affected. The melted portion of Yanzhuang is also essentially void of radiogenic 4He (10 ± 4 × 10−8 cm3 STP/g) but it has retained some 80% of its radiogenic 40Ar, presumably because in the melt the increase of the diffusion length more than compensated the increase of the diffusion constant.