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Sm-Nd and Rb-Sr Isotopic Studies of Meteorite Kalahari 009: An Old VLT Mare Basalt

Abstract

Lunar meteorite Kalahari 009 is a fragmental basaltic breccia contain ing various very-low-Ti (VLT) mare basalt clasts embedded in a fine-g rained matrix of similar composition. This meteorite and lunar meteorite Kalahari 008, an anorthositic breccia, were suggested to be paired mainly due to the presence of similar fayalitic olivines in fragment s found in both meteorites. Thus, Kalahari 009 probably represents a VLT basalt that came from a locality near a mare-highland boundary r egion of the Moon, as compared to the typical VLT mare basalt samples collected at Mare Crisium during the Luna-24 mission. The concordant Sm-Nd and Ar-Ar ages of such a VLT basalt (24170) suggest that the extrusion of VLT basalts at Mare Crisium occurred 3.30 +/- 0.05 Ga ag o. Previous age results for Kalahari 009 range from approximately 4.2 Ga by its Lu-Hf isochron age to 1.70?0.04 Ga of its Ar-Ar plateau ag e. However, recent in-situ U-Pb dating of phosphates in Kalahari 009 defined an old crystallization age of 4.35+/- 0.15 Ga. The authors su ggested that Kalahari 009 represents a cryptomaria basalt. In this r eport, we present Sm-Nd and Rb-Sr isotopic results for Kalahari 009, discuss the relationship of its age and isotopic characteristics to t hose of other L-24 VLT mare basalts and other probable cryptomaria ba salts represented by Apollo 14 aluminous mare basalts, and discuss it s petrogenesis

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