Premium
Laser argon‐40‐argon‐39 age determinations of Luna 24 mare basalts
Author(s) -
BURGESS RAY,
TURNER GRENVILLE
Publication year - 1998
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.1998.tb01697.x
Subject(s) - basalt , radiogenic nuclide , geology , isotopes of argon , breccia , lunar mare , geochemistry , argon , lithology , radiometric dating , mineralogy , chemistry , mantle (geology) , organic chemistry
— The ages of seven rock fragments from the soil fraction of the Luna 24 core have been determined using a laser 40 Ar‐ 39 Ar stepped heating technique. The investigated lithologies include fragments of fine‐grained ophitic basalt, coarse‐grained basalt, metabasalts and a regolith breccia. Most of the samples contain nonradiogenic Ar components of variable 36 Ar/ 40 Ar composition. These surface‐correlated trapped components are predominantly released at low temperature and can be distinguished from volume‐correlated radiogenic and cosmogenic components released at higher temperature during stepped heating. Binary mixtures of radiogenic and cosmogenic Ar components give linear correlations on 36 Ar t / 40 Ar‐ 39 Ar/ 40 Ar diagrams from which the age and 36 Ar/ 40 Ar value of trapped Ar can be determined. The ages obtained span a narrow range between 3.18‐3.28 Ga with an average of 3.22 ± 0.04 Ga. This is interpreted as being the age of the basalts at the Luna 24 sampling site. Systematic age differences between lithologies were not detected; however, a single age of 2.93 Ga obtained from a coarse‐grained basalt hints at the possibility of younger volcanism. The results of this work effectively triple the chronological information available for Mare Crisium and are within the range of radiometric age measurements of Luna 24 mare basalts obtained previously.