Lunar and Planetary Science XXXIV ( 2003 ) 1454 . pdf

Introduction: The A16 (Apollo16) site in the lunar nearside highlands is 220 km from the nearest mare. Thus it is no surprise that mare basalt samples are uncommon at the site. Here, we present the petrography and geochemistry of 5 new mare basalt samples found at the A16 site. We also discuss possible provenances of all A16 mare basalt samples using high-resolution global data for the distribution of Fe and Ti on the lunar surface derived from Clementine UV-VIS data [1-2]. Background: The maria nearest to the A16 site are Sinus Asperitatis (220 km) and Mare Nectaris (~400 km). The A16 regolith consists of basin ejecta from Nec-taris and Imbrium, and possibly Serenitatis, mixed with pre-Nectarian regolith [3-4]. Two formations were sampled at the A16 site, the Cayley Formation and the more feldspathic Descartes Formation sampled at North Ray Crater (NRC). Only 20 small samples of crystalline mare basalts have been reported from A16 [5-10]. Most A16 mare material occurs as glass in the finest soil fractions [5,11]; estimates of the fraction of mare material in the <1 mm fines range from 5-6 % [12-13]. Descriptions: Sample 60503,22-7 is a high-Ti ba-salt (~9 % TiO 2 ; Table 1) with ilmenite, olivine, a trace of Cr-spinel and Fe-metal, and xenocrystic olivine and pyroxene in a glassy matrix. Its REE-pattern and Cr, Sc, Sm, and Ba concentrations [14] are similar to those of A17 high-Ti basalts, but the TiO 2 concentration is slightly less. Sample 60603,10-16 is a very-high-Ti (VHT) basaltic vitrophyre with ilmenite, olivine, and Cr-spinel grains in a glassy matrix. Its major-and trace-element composition is consistent with VHT picritic glasses such as A12 and A14 red-black glass [15]. Sample 62243,10-22 is a very-low-Ti (VLT) vitrophyre with one area of rapidly crystallized, aluminous pyroxene. Its bulk chemical composition is similar to those of A17 VLT mare basalts. Sample 65703,9-13 is a VLT basalt with plagioclase, pyroxene, and olivine, and trace faya-lite, Cr-spinel, troilite, and ilmenite. Its chemical composition is similar to Luna 24-like VLT mare basalts except its REE-pattern which does not match. Sample 60053,2-9 has a high-Al basalt composition, similar to A14 group 5 high-Al basalts [16]. It is composed of pla-gioclase, pyroxene, ilmenite, and a silica phase, with trace amounts of troilite, and an area of silica-hedenbergite-fayalite mesostasis (symplectite). Discussion: The mare basalt fragments previously found at the A16 site are of three types: A17-like high-Ti basalts, A12-like …