Itawa Bhopji (L3-5) chondrite regolith breccia: Fall, classification, and cosmogenic records

Abstract

A stony meteorite fell at Itawa Bhopji, Rajasthan, India on 2000 May 30. This is the fifth recorded fall in a small area of Rajasthan during the past decade. The meteorite is an ordinary chondrite with light clasts in a dark matrix, consisting of a mixture of equilibrated (mainly type 5) and unequilibrated components. Olivine is Fa24-26 and pyroxene Fs20-22 but, within the unequilibrated components, olivine (Fa5-29) and low calcium pyroxene (Fs5-37) are highly variable. Based on petrographic studies and chemical analyses, it is classified as L(3-5) regolith breccia. Studies of various cosmogenic records, including several gamma-emitting radionuclides varying in half-life from 5.6 day 52Mn to 0.73 Ma 26Al, tracks and rare gases have been carried out. The exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19.6 Ma. The track density varies by a factor of ~3 (from 4 to 12 x 10^6/cm^2) within the meteorite, indicating a preatmospheric body of ~9 cm radius (corresponding to a meteoroid mass of ~11 kg) and small ablation (1.5 to 3.6 cm). Trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite. Large excess of neutron-produced 82Kr and 128Xe in both the light and the dark lithology but very low 60Co, indicating low neutron fluxes received by the meteoroid in the interplanetary space, are clear signatures of an additional irradiation on the parent body.