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Marti et al. 1983
Marti, K., Jost, D.T., Aeschlimann, U., Eberhardt, P., Geiss, J., Geögler, N., Laul, J.C., Ma, M.-S., Schmitt, R.A. and Taylor, G.J. (1983). Pieces of the ancient lunar crust: Ages and composition of clasts in consortium breccia 67915. Journal of Geophysical Research 88: doi: 10.1029/JS088iS02p0B165. issn: 0148-0227.

We discuss the composition and chronology of clasts representing three minor lithologies in consortium breccia 67915. The lithologies studied are: sodic ferrogabbro, pristine troctolitic anorthosite (67915,26), and granulitic troctolitic anorthosite (67916,67). These lithologies were presumed to represent samples of the ancient lunar crust. The pristine troctolitic anorthosite, a typical member of the pristine anorthosite suite, contains little or no trapped liquid consistent with its two -phase mineralogy. The plagioclase separates have 39Ar-40Ar plateau ages of 4.10¿0.06 b.y., and a final rise in the age pattern may represent a 'memory' of the earlier evolution. The granulitic troctolitic anorthosite, which has 13 times larger REE abundances, displays a continuous rise of the 40Ar/39Ar ratio. The last 25% of the 39Ar release data establish a minimum age of >3.5 b.yu., but the 244Pu/Nd chronology suggests an age of ~4.3 b.y. The sodic ferrogabbro samples, which appear to be members of the Mg-gabbronorite group of pristine rocks, show large Ar losses but indicate plateaus in the low-temperature data, suggesting a metamorphic event more recently than 260 m.y. ago, a time that is consistent with the North Ray impact event 50 m.y. ago.

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Journal of Geophysical Research
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American Geophysical Union
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