U-Pb and Lu-Hf systematics of Antarctic meteorites

U-Th-Pb analyses for the chondrites-ALHA77278 (LL3), Bishunpur (LL3) and McKinney (L4) have been performed in order to evaluate the effects of weathering under Antarctic conditions on the U-Th-Pb system. The ALHA77278 data indicate that, although this sample is apparently less contaminated than McKinney, a normal "find", it may still contain as much as 50 ppb terrestrial Pb. In addition, both meteorites seem to have experienced some leaching of U, Th, and/or Pb, and perhaps some preferential leaching of Pb isotopes. Lu-Hf analyses of 3 Antarctic eucrites-ALH-77302,Yamato-74159 and Yamato-74450 have been performed to evaluate the effects of Antarctic weathering on this system. In addition, the Bouvante eucrite was analyzed in an attempt to improve the precision of the solar system initial ^(Hf)/^(Hf) ratio as determined from a whole-rock isochron for eucrite meteorites. The most weathered sample, ALH-77302 appears to have suffered terrestrial Lu loss, whereas data from the two Yamato eucrites plot precisely on the eucrite whole-isochron. When the data from the two Yamato meteorites and Bouvante are included with those previously obtained from other eucrites, a revised ^(Hf)/^(Hf) initial of 0.27978±9 (2σ) is obtained, 25% more precise than that previously reported. A revised half-life of 3.57±0.14 (2σ)×(10)^ a for ^(Lu) is also obtained by inclusion of the new data