Noble gas, nitrogen composition and cosmic ray exposure history of two eucrites Vissannapeta, Piplia Kalan and one howardite Lohawat

We have carried out detailed noble gases and nitrogen isotopic study of two eucrites Vissannapeta, Piplia Kalan and one howardite Lohawat. Neon is mainly produced by Galactic Cosmic Ray (GCR) in all the three meteorites. The estimated cosmic ray exposure ages are 23.8 +/- 6.1 Ma, 28.4 +/- 8.1 Ma and 46.4 +/- 17.3 Ma for Piplia Kalan, Vissannapeta and Lohawat, respectively. Light nitrogen composition is present in Vissannapeta and Lohawat, while heavy nitrogen composition is observed in Piplia Kalan. The nitrogen is distinctly trapped in the eucrites. Elemental ratios of the trapped noble gases such as argon, krypton and xenon together with nitrogen composition in eucrites indicate their distinct source region in Vesta. A younger potassium-argon age for the eucrites (3.71 +/- 0.42 Ga for Vissannapeta and 3.60 +/- 0.15 Ga for Piplia Kalan) than the solar system formation age, indicates partial loss of the radiogenic argon during the evolutionary stages of these meteorites plausibly due to impact metamorphic events. The radiogenic ages derived from the He-4 are less than 1 Ma suggesting loss of helium from the eucrites.