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

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 Fa(24-26) and pyroxene Fs(20-22) but, within the unequilibrated components, olivine (Fa(5-29)) and low calcium pyroxene (Fs(5-37)) 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 (52)Mn to 0.73 Ma (26)Al 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 similar to3 (from 4 to 12 x 10(6)/cm(2)) within the meteorite, indicating a preatmospheric body of similar to9 cm radius (corresponding to a meteoroid mass of similar to11 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 (82)Kr and (128)Xe in both the light and the dark lithology but very low (60)Co, indicating low neutron fluxes received by the meteoroid in the interplanetary space, are clear signatures of an additional irradiation on the parent body.