A Crustal Rock Clast in Magnesian Anorthositic Breccia, Dhofar 489 and Its Excavation from a Large BasinWe report the mineralogy and Ar-Ar age of a spinel troctolite clast with a granulitic texture found in the Dofar 489 lunar meteorite. This anothositic breccia contained magnesian mafic silicates not common in ferroan anorthosites (FAN) from the Feldspathic Highlands Terrane (FHT) of Joliff et al. The Ar-Ar ages of most FANs in the Apollo sample collection from the Procellarum KREEP Terrane (PKT) and FHT of the near-side of the Moon were reset at around 3.9 Gyr. by the basin forming event of Imbrium. From the older Ar-Ar age of Dho 489, we propose that a large basin formation other than the Imbrium basin may have mixed deep crustal rocks such as spinel troctolites with "pure" anrthosites to produce a magnesian anorthosite brecca. This model is in line with a proposal by Bussey and Spudis, who reported that inner rings of large basins display massifs of nearly pure anorthosites.
Document ID
20040062082
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Takeda, Hiroshi (Chiba Inst. of Tech. Narashino, Japan)
Bogard, D. D. (NASA Johnson Space Center Houston, TX, United States)
Yamaguchi, Akira (National Inst. of Polar Research Tokyo, Japan)