Lewis Cliff 86360: An Antarctic L-chondrite with a terrestrial age of 2.35 million years

Abstract

We measured the concentrations of the cosmogenic radionuclides 10Be (half-life = 1.51 × 106 a), 26Al (7.05 × 105 a) and 36CI (3.01 × 105 a) in Lewis Cliff (LEW) 86360, an L-chondrite from the Lewis Cliff stranding area, East Antarctica. In addition, the concentrations and isotopic compositions of He, Ne and Ar were measured. The combined results yield a terrestrial age of 2.35 ± 0.15 Ma. Only one other stony meteorite with a similar terrestrial age (∼2 Ma) is known from the Allan Hills stranding area (ALH 88019), whereas all previously dated stony meteorites from Antarctica are younger than.1 Ma. We argue that LEW 86360 spent most of its terrestrial residence time deep inside the ice, near the basis of the glacier, where ice flow rates are much lower than at the surface. The terrestrial ages of LEW 86360 and ALH 88019 are consistent with existing hypotheses concerning the stability and persistence of the East Antarctic ice sheet.