Geochemistry, Mineralogy, and Petrology of Boninitic and Komatiitic Rocks on the Mercurian Surface: Insights into the Mercurian Mantle

1,2,3Kathleen E. Vander Kaaden, 1,3Francis M. McCubbin, 4Larry R. Nittler, 5Patrick N. Peplowski, 4Shoshana Z. Weider, 4Elizabeth A. Frank,6Timothy J. McCoy
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.11.041]
1Institute of Meteoritics, Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA.
2Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA
3NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, TX 77058, USA.
4Department of Terrestrial Magnetism, Carnegie Institution of Washington, DC 20015, USA.
5The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
6Department of Mineral Sciences, National Museum of Natural History, 10th and Constitution Aves. NW, Smithsonian Institution, Washington, DC 20560, USA.
Copyright Elsevier

Orbital data from the MESSENGER mission to Mercury have facilitated a new view of the planet’s structure, chemical makeup, and diverse surface, and have confirmed Mercury’s status as a geochemical endmember among the terrestrial planets. In this work, the most recent results from MESSENGER’s X-Ray Spectrometer, Gamma-Ray Spectrometer, and Neutron Spectrometer have been used to identify nine distinct geochemical regions on Mercury. Using a variation on the classical CIPW normative mineralogy calculation, elemental composition data is used to constrain the potential mineralogy of Mercury’s surface; the calculated silicate mineralogy is dominated by plagioclase, pyroxene (both orthopyroxene and clinopyroxene), and olivine, with lesser amounts of quartz. Petrologically, the rocks on the surface of Mercury are highly diverse and vary from komatiitic to boninitic. The high abundance of alkalis on Mercury’s surface results in several of the nine regions being classified as alkali-rich komatiites and/or boninites. In addition, Mercury’s surface terranes span a wide range of SiO2 values that encompass crustal compositions that are more silica-rich than geochemical terranes on the Moon, Mars, and Vesta, but the range is similar to that of Earth. Although the composition of Mercury’s surface appears to be chemically evolved, the high SiO2 content is a primitive feature and a direct result of the planet’s low oxygen fugacity.

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