Bhawad LL6 chondrite: chemistry, petrology,noble gases, nuclear tracks, and cosmogenic radionuclides

Abstract

Chemical and mineral analysis of the Bhawad chondrite, which fell in Rajasthan in 2002, suggest that this stone belongs to LL6 group of chondrites. Based on helium, neon, and argon isotopes, it has a cosmic ray exposure age of 16.3 Ma. The track density in the olivines shows a narrow range of 1.7-6.8 times 10⁶/cm². The ²²Na/²⁶Al ratio of 1.13 is about 25% lower than the solar cycle average value of about 1.5, but is consistent with irradiation of the meteoroid to modulated galactic cosmic ray fluxes as expected for a fall around the solar maximum. The cosmogenic records indicate a pre-atmospheric radius of about 7.5 cm. Based on U/Th-⁴He and K-⁴⁰Ar, the gas retention ages are low (about 1.1 Ga), indicating a major thermal event or shock event that lead to the complete loss of radiogenic ⁴He and ⁴⁰Ar and the partial loss of radiogenic ¹²⁹Xe and fission Xe from ²⁴⁴Pu.