Ar-40/Ar-39 Ages for Maskelynites and K-Rich Melt from Olivine-Rich Lithology in (Kanagawa) ZagamiWe report Ar/Ar release patterns for small maskelynite grains and samples of a K-rich phase separated from the basaltic shergottite Zagami. The purpose of the work is to investigate the well-known discrepancy between published Ar/Ar ages of Zagami, >200 Ma, and its age of approx. 170 Ma as determined by other methods [1-6]. Niihara et al. [7] divide less abundant darker material present in Zagami into an olivine-rich lithology (ORL), from which most of our samples came, and a pyroxene-rich one (Dark Mottled-Lithology: DML) [8, 9]. ORL consists of vermicular fayalitic olivine, coarse-grained pyroxene, maskelynite, and a glassy phase exceptionally rich in K (up to 8.5 wt%), Al, and Si, but poor in Fe and Mg. The elemental composition suggests a late-stage melt, i.e., residual material that solidified late in a fractional crystallization sequence. Below we refer to it as "K-rich melt." The K-rich melt contains laths of captured olivine, Ca-rich pyroxene, plagioclase, and opaques. It seemed to offer an especially promising target for Ar-40/Ar-39 dating.
Document ID
20130011089
Acquisition Source
Johnson Space Center
Document Type
Conference Paper
Authors
Park, J. (Lunar and Planetary Inst. Houston, TX, United States)
Herzog, G. F. (Rutgers Univ. Piscataway, NJ, United States)
Nyquist, L. E. (NASA Johnson Space Center Houston, TX, United States)
Lindsay, F. (Rutgers Univ. Piscataway, NJ, United States)
Turrin, B. (Rutgers Univ. Piscataway, NJ, United States)
Swisher, C. C., III (Rutgers Univ. Piscataway, NJ, United States)
Delaney, J. S. (Rutgers Univ. Piscataway, NJ, United States)
Shih, C.-Y. (Jacobs Technologies Engineering Science Contract Group Houston, TX, United States)
Niihara, T. (Lunar and Planetary Inst. Houston, TX, United States)
Misawa, K. (National Inst. of Polar Research Tokyo, Japan)