Time Differences in the Formation of Meteorites as Determined from the Ratio of Lead-207 to Lead-206
Time Differences in the Formation of Meteorites as Determined from the Ratio of Lead-207 to Lead-206
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DOI：
10.1126/science.180.4092.1279
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发表时间：
1973-06
期刊：
影响因子：
56.9
通讯作者：
M. Tatsumoto;R. Knight;C. Allègre
中科院分区：
文献类型：
--
作者：
M. Tatsumoto;R. Knight;C. Allègre
对陨石中铅同位素组成和铀、钍、铅浓度的测量是为了获得这些太阳系成员更精确的放射性年龄。新测定的峡谷Diablo陨硫铁铅同位素组成值为：206 Pb/204 Pb = 9.307、207 Pb/2 O 4 Pb = 10.294、208 Pb/204 Pb = 29.476。安格拉杜斯雷斯、Sioux County和新拉雷多无球粒陨石的铅是非常放射成因的，206 Pb/204 Pb值约为200，铀-钍-铅系统几乎一致。根据新测定的原始铅值和新报道的235 U和838 U衰变常数，从单阶段207 Pb/206 Pb等时线计算出的陨石年龄为4.528 x 109年（苏郡和新拉雷多）和4.555 x 109年（安格拉杜斯雷斯）。当用帕特森使用的铀衰变常数计算时，这两个年龄分别为4.593 x 109年和4.620 x 109年，因此比帕特森报告的4.55 x 109年要老40到70 x 106年。安格拉杜斯雷斯和其他两颗陨石之间的年龄差为27 x 106年，这与安格拉杜斯雷斯的初始87 Sr/86 Sr比值与Papanastassiou和Wasserburg观察到的7颗玄武质无球粒陨石之间的差异是一致的。这一时间差也与1291- 1291年的年代学所确定的时间差相当。普通榴辉岩（H5和L 6）的年龄范围为4.52至4.57 × 109年，这里也指出了母体形成或后期变质事件的时间差异。碳质方解石（C2和C3）似乎含有较年轻的铅成分。
Measurements of the lead isotopic composition and the uranium, thorium, and lead concentrations in meteorites were made in order to obtain more precise radiometric ages of these members of the solar system. The newly determined value of the lead isotopic composition of Canyon Diablo troilite is as follows: 206Pb/204Pb = 9.307, 207Pb/2O4Pb = 10.294, and 208Pb/204Pb = 29.476. The leads of Angra dos Reis, Sioux County, and Nuevo Laredo achondrites are very radiogenic, the 206Pb/204Pb values are about 200, and the uranium-thorium-lead systems are nearly concordant. The ages of the meteorites as calculated from a single-stage 207Pb/206Pb isochron based on the newly determined primordial lead value and the newly reported 235U and 838U decay constants, are 4.528 x 109 years for Sioux County and Nuevo Laredo and 4.555 x 109 years for Angra dos Reis. When calculated with the uranium decay constants used by Patterson, these ages are 4.593 x 109 years and 4.620 x 109 years, respectively, and are therefore 40 to 70 x 106 years older than the 4.55 x 109 years age Patterson reported. The age difference of 27 x 106 years between Angra dos Reis and the other two meteorites is compatible with the difference between the initial 87Sr/86Sr ratio of Angra dos Reis and that of seven basaltic achondrites observed by Papanastassiou and Wasserburg. The time difference is also comparable to that determined by 1291-129Xe chronology. The ages of ordinary chondrites (H5 and L6) range from 4.52 to 4.57 x 109 years, and, here too, time differences in the formation of the parent bodies or later metamorphic events are indicated. Carbonaceous chondrites(C2 and C3) appear to contain younger lead components.