³⁹Ar/⁴⁰Ar systematics of Allende inclusions.

The Ar isotopic contents of individual mineral grains were measured in four neutron irradiated samples from Allende: two coarse-grained Ca-Al-rich inclusions; one fine-grained Ca-Al-rich inclusion; one sample with matrix and miscellaneous chondrules. The following K/Ar ages were obtained: matrix 3500 + or - 200 m.y.; three miscellaneous chondrules, 4400 + or - 100 m.y., 4000 + or - 100 m.y., and 4400 + or - 0.1 m.y; and the fine-grained inclusion 3839, 4500 + or - 200 m.y., all after degassing low Ar retentive sites by pre-heating at 675^oC. The minerals in the coarse-grained Ca-Al-rich inclusions have ubiquitous Cl, less than approx 10 p.p.m. K and apparent ages ranging from 4600 m.y. to well over 10 000 m.y. Possible explanations for these apparent ages are discussed.-P.Br.