アイテム詳細

要旨

The trapped noble gas record of 57 enstatite chondrites (E chondrites) has been investigated. Basically, two different gas patterns have been identified dependent on the petrologic type. All E chondrites of type 4 to 6 show a mixture of trapped common chondritic rare gases (Q) and a subsolar component (range of elemental ratios for E4-6 chondrites: Ar-36/Xe-132 = 582 +/- 270 and Ar-36/Kr-84 = 242 +/- 88). E3 chondrites usually contain Q gases, but also a composition with lower Ar- 36/Xe-132 and Ar-36/Kr-84 ratios, which we call sub-Q (Ar- 36/Xe-132 = 37.0 +/- 18.0 and Ar-36/Kr-84 = 41.7 +/- 18.1). The presence of either the subsolar or the sub-Q signature in particular petrologic types cannot be readily explained by parent body metamorphism as postulated for ordinary chondrites. We therefore present a different model that can explain the bimodal distribution and composition of trapped heavy noble gases in E chondrites. Trapped solar noble gases have been observed only in some E3 chondrites. About 30% of each group, EH3 and EL3 chondrites, amounting to 9% of all analyzed E chondrites show the solar signature. Notably, only one of those meteorites has been explicitly described as a regolith breccia.