The Magmatic History of an Aubrite Parent Asteroid: Evidence From Igneous Clasts and Trace Elements

• Main Author: Wheelock, Maya Monica
• Format: Text
• Language: English
• Published: UNM Digital Repository 1990
• Subjects: Geology; Antarctic; Pena; Antarc*
• Online Access: https://digitalrepository.unm.edu/eps_etds/242; https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1255&context=eps_etds

Norton County aubrite contains numerous igneous-textured clasts that survived severe brecciation. These clasts were studied in order to obtain information about the suite of original igneous lithologies that crystallized on an aubrite parent body. The majority of igneous clasts are pyroxenites (enstatite, with minor diopside, +/- forsterite) and orthopyroxenites (enstatite, +/- forsterite). Phase relations and textural evidence are consistent with formation from a nearly pure enstatite magma body or magma ocean, at (or near) the surface of the parent body. A new sulfide-dominated lithology was identified in Norton County. The sulfide portion is dominated by coarse-grained oldhamite (CaS) containing rounded inclusions of other sulfides. The silicate portion is dominated by forsterite but may also contain enstatite and plagioclase. Textural evidence suggests that they formed from immiscible Ca-rich sulfide melt droplets in an aubrite parent magma; this conclusion is consistent with published experimental results. Ion microprobe analysis confirms that oldhamite is the main REE carrier in aubrites, with abundances of about 200 times chondritic values; it has a pronounced negative Eu anomaly. Ferromagnesian alabandite, diopside and plagioclase are REE carriers of secondary importance. REE patterns for bulk samples of Norton County may be dominated b small amounts ( Igneous-textured clasts were also identified in other aubrites. Norton County and Bishopville are dominated by diopside-bearing pyroxenites, while Pena Blanca Spring, Mayo Belwa, Mount Edgerton and Antarctic aubrites are dominated by forsterite-bearing orthopyroxenites.