AR-39-AR-40 DATING OF 2 LUNAR GRANITES - THE AGE OF COPERNICUS

被引：36

作者：

BOGARD, DD ^{[1
]}

GARRISON, DH ^{[1
]}

SHIH, CY ^{[1
]}

NYQUIST, LE ^{[1
]}

机构：

[1] LOCKHEED ENGN & SCI CO,HOUSTON,TX 77258

来源：

GEOCHIMICA ET COSMOCHIMICA ACTA | 1994年 / 58卷 / 14期

关键词：

D O I：

10.1016/0016-7037(94)90181-3

中图分类号：

P3 [地球物理学]; P59 [地球化学];

学科分类号：

0708 ; 070902 ;

摘要：

Previous investigations have suggested that KREEP glass found in 12033 and other Apollo 12 soils was ejected from the crater Copernicus and deposited in a ray across this site. Soil fragment 12033,507 has been described as having a core of felsite (granitic) composition with a KREEP-glass shell. Ar-39-Ar-40 dating of a sample of this granite material shows almost complete resetting 800 +/- 15 Ma ago. We interpret this age as giving the most precise determination to date for the formation time of Copernicus. Cosmic ray exposure ages of the granite and associated KREEP glass in soil 12033, about 250 Ma, are much less than the K-Ar age and suggest a complex, postejection burial history. The Ar-39-Ar-40 age of another granite fragment, 14303,204, is determined to be in the range 3.80-3.85 Ga. This age is in agreement with Ar-39-Ar-40 ages determined for a few other lunar granites and is interpreted to represent resetting by a large, basin-forming impact, probably Imbrium.

引用

页码：3093 / 3100

页数：8

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