LEWIS-CLIFF-86360 - AN ANTARCTIC L-CHONDRITE WITH A TERRESTRIAL AGE OF 2.35 MILLION YEARS

We measured the concentrations of the cosmogenic radionuclides Be-10 ( half-life = 1.51 x 10(6) a), Al-26 (7.05 x 10(5) a) and Cl-36 (3.01 x 10(5) a) in Lewis Cliff(LEW) 86360, an L-chondrite from the Lewis Clif f stranding area, East Antarctica. In addition, the concentrations and isotopic compositions of He, Ne and Ar were measured. The combined re sults yield a terrestrial age of 2.35 +/- 0.15 Ma. Only one other ston y meteorite with a similar terrestrial age (similar to 2 Ma) is known from the Allan Hills stranding area (ALH 88019), whereas all previousl y dated stony meteorites from Antarctica are younger than 1 Ma. We arg ue that LEW 86360 spent most of its terrestrial residence time deep in side the ice, near the base of the glacier, where ice flow rates are m uch lower than at the surface. The terrestrial ages of LEW 86360 and A LH 88019 are consistent with existing hypotheses concerning the stabil ity and persistence of the East Antarctic ice sheet.