EXPOSURE HISTORY OF THE LUNAR METEORITE, ELEPHANT-MORAINE-87521

We report the noble gas concentrations and the Al-26, Be-10, Cl-36, an d Ca-41 activities of the Antarctic lunar meteorite Elephant Moraine 8 7521. Although the actual exposure history of the meteorite may have b een more complex, the following model history accounts satisfactorily for the cosmogenic nuclide data: A first stage of lunar irradiation fo r approximately 1 Ma at a depth of 1-5 g/cm2 followed, not necessarily directly, by a second one for 26 Ma at approximately 565 g/cm2; launc h from the Moon less than 0.1 Ma ago; and arrival on Earth 15-50 ka ag o. The small concentration of trapped gases shows that except for some material that may have been introduced at the moment of launch, EET 8 7521 spent <1 Ma at a lunar depth <1 g/cm2. EET 87521 has a K/Ar age i n the range 3.0-3.4 Ga, which is typical for lunar mare basalts.