Japan Geoscience Union Meeting 2015

Presentation information


Symbol P (Space and Planetary Sciences) » P-PS Planetary Sciences

[P-PS22] Formation and evolution of planetary materials in the solar system

Wed. May 27, 2015 5:15 PM - 6:00 PM A02 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Shoichi Itoh(Graduate school of Science, Kyoto University), Tomohiro Usui(Department of Earth and Planetary Sciences,Tokyo Institute of Technology), Yusuke Seto(Graduate School of Science, Kobe University), Masaaki Miyahara(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University), Makoto Kimura(Faculty of Science, Ibaraki University), Eiji Ohtani(Department of Earth and Planetary Materials Science, Graduate School of Science, Tohoku University), Hitoshi Miura(Graduate School of Natural Sciences, Department of Information and Biological Sciences, Nagoya City University), Hikaru Yabuta(Osaka University, Department of Earth and Space Science), Chair:Shoichi Itoh(Graduate school of Science, Kyoto University), Masaaki Miyahara(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University)

5:45 PM - 5:48 PM

[PPS22-P11] A Partial Melting Study of an Ordinary Chondrite Composition with Application to the Felsic Asteroidal Crust Formation

3-min talk in an oral session

*Tomohiro USUI1, John Jones2, Mittlefehldt David2 (1.Tokyo Institutue of Technology, 2.NASA)

Keywords:asteroid, crust, ordinary chondrite

Melting experiments of a synthesized, alkali-bearing, H-chondrite composition were conducted at ambient pressure with three distinct oxygen fugacity conditions (IW-1, IW and IW+2). Oxygen fugacity conditions significantly influence the compositions of partial melts. Partial melts at IW-1 are distinctly enriched in SiO2 relative to those of IW and IW+2 melts. The silica-enriched, reduced (IW-1) melts are characterized by high alkali contents and have silica-oversaturated compositions. In contrast, the silica-depleted, oxidized (?IW) melts, which are also enriched in alkali contents, have distinctly silica-undersaturated compositions. These experimental results suggest that alkali-rich, felsic, asteroidal crusts as represented by paired achondrites Graves Nunataks 06128 and 06129 should originate from a low-degree, relatively reduced partial melt from a parent body having near-chondritic compositions. Based on recent chronological constraints and numerical considerations as well as our experimental results, we propose that such felsic magmatism should have occurred in a parent body that is smaller in size and commenced accreting later than those highly differentiated asteroids having basaltic crusts and metallic cores.

Figure caption:
Summary of magmatic conditions of achondrite suites in terms of degree of melting and fO2 (relative to IW). See [1] for details.

[1] Usui, T., Jones, J. H., Mittlefehldt, D. W. A partial melting study of an ordinary (H) chondrite composition with application to the unique achondrite Graves Nunataks 06128 and 06129. Meteoritics and Planetary Sciences, in press.