HR: 0800h
AN: P41C-08    [Abstracts]
TI: Single Chondrule K/Ar ages of Mexican Meteorites Using ID-TIMS.
AU: * Hernandez, M
EM: msol@geologia.unam.mx
AF: Instituto de Geologia, Universidad Nacional Autonoma de Mexico, Circuito de la Investigacion Cientifica s/n, Cd. Universitaria, D.F., 04510, Mexico
AU: Sole, J
EM: jsole@geologia.unam.mx
AF: Instituto de Geologia, Universidad Nacional Autonoma de Mexico, Circuito de la Investigacion Cientifica s/n, Cd. Universitaria, D.F., 04510, Mexico
AB: We have determined the K/Ar ages of two H5 ordinary meteorites: Cosina and Nuevo Mercurio, neither dated until this study. We analyzed several single chondrules - weighing few milligrams - of each meteorite. Ages were obtained by using very precise K content determined by isotope dilution mass spectrometry. The K content in chondrules ranges between 650 and 1400 ppm. The 40Ar was measured by static vacuum noble gas mass spectrometry. Samples were fused with an infrared CO2 laser. Chondrule ages vary from 3.66 to 4.59 Ga for Cosina and from 4.20 to 4.87 Ga for Nuevo Mercurio. A comparison between our data and the published K/Ar ages of H and L whole rocks shows that dates obtained from single chondrules are older than those obtained from whole rocks and seem to preserve older events not evidenced in the WR ages. This implies that chondrules can preserve K/Ar ages very close to U-Pb crystallization ages.
DE: 1100 GEOCHRONOLOGY
DE: 1115 Radioisotope geochronology
DE: 1194 Instruments and techniques
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly