Ar–Ar ages and trapped Ar components in Martian shergottites RBT 04262 and LAR 06319

摘要: Abstract We made 39Ar–40Ar (Ar–Ar) analyses of whole rock (WR) and mineral samples two Martian shergottites, RBT 04262 (RBT) LAR 06319 (LAR), in order to determine their Ar–Ar ages the 40Ar/36Ar ratios trapped Ar they contain. All released (excess) 40Ar 36Ar suggested older than formation ages. Because components having different were at extraction temperatures, we utilized only a portion data derive preferred obtain 171 ± 8 Ma for plagioclase 163 ± 13 Ma rock. identify components. At low particularly plagioclase, Trapped-A with 285 ± 3 was released, believe this is most likely absorbed terrestrial air. high pyroxene, Trapped-B 1813 ± 127 released. The poikilitic/non-poikilitic texture presence large pyroxene oikocrysts allowed clear definition Trapped-B. This component Martian, its isotopic similarity atmospheric composition suggests that it may represent incorporated into shergottite melt via crustal rocks. partitioned constant molar ratio K/36ArTr = 33.2 ± 9.5 × 106 04262, 80 ± 21 × 106 06319. mixed proportions could give apparently intermediate compositions commonly observed shergottites.