A Caltech Library Service

Rb-Sr age of troctolite 76535

Papanastassiou, D. A. and Wasserburg, G. J. (1976) Rb-Sr age of troctolite 76535. In: Proceedings of the Seventh Lunar Science Conference. Vol.2. Pergamon Press , New York, NY, pp. 2035-2054. ISBN 9780080217710.

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item:


We have studied the Rb-Sr systematics for the troctolite 76535 in phases covering a wide range of Rb and Sr concentrations. The Rb-Sr data define a precise linear array for most of the samples. Excluding two samples which are distinctly anomalous we obtain a line corresponding to an age of 4.61 ± 0.07 AE and an initial ⁸⁷Sr/⁸⁶Sr of 0.69900 + 0.00003. The Rb-Sr age of 4.55 ± 0.10 AE for the dunite (72417) and the Rb-Sr age of the troctolite are in approximate agreement and permit an interpretation that these rocks formed during a single major lunar differentiation which presumably produced an anorthositic-gabbroic lunar crust and layered upper mantle. Other dating methods (K-Ar, Sm-Nd) yield distinctly younger ages for the troctolite of 4.25 AE which are not in agreement with the Rb-Sr age. The causes of this discrepancy are not understood. The U-Pb system shows a young disturbance in the neighborhood of ~4.0 AE. Whereas the K-Ar ages could previously be considered as due to partial degassing of 76535 during the terminal lunar cataclysm, the Sm-Nd data cannot easily be interpreted in this fashion. Assuming that the ages of 4.61 and 4.25 AE are meaningful, our preferred interpretation is that the troctolite was formed at 4.61 AE and remained at elevated temperatures until 4.25 AE at which time it was excavated by a major impact. Throughout the interval 4.61-4.25 AE, ⁴⁰Ar diffused out of the rock and Sm and Nd exchanged chemically and isotopically; however, Rb-Sr systems protected inside olivine crystals remained closed. Except for some inconclusive U-Pb results and peculiarities in the ⁴⁰Ar-³⁹Ar data there are no results which clearly show that the troctolite was affected by the terminal lunar cataclysm.

Item Type:Book Section
Related URLs:
URLURL TypeDescription
Wasserburg, G. J.0000-0002-7957-8029
Additional Information:We thank A. L. Albee, R. F. Dymek, and A. J. Gancarz for constructive discussions. Expertise by one of these workers on the properties of platinum sheaths has been most useful. We thank L. E. Nyquist and N. M. Evensen, who provided constructive detailed reviews which hopefully have resulted in significant improvements in the paper. This work was supported by NASA Grant No. NGL-05-002-188. Contribution No. 2750, Division of Geological and Planetary Sciences.
Funding AgencyGrant Number
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences2750
Record Number:CaltechAUTHORS:20221129-190644082
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118102
Deposited By: Tony Diaz
Deposited On:29 Nov 2022 19:43
Last Modified:29 Nov 2022 19:43

Repository Staff Only: item control page