| タイトル | Excess Ar-40 in the Zagami Shergottite: Does It Reveal Crystallization History? |
| 本文（外部サイト） | http://hdl.handle.net/2060/20070021571 |
| 著者（英） | Bogard, Donald D.; Park, Jisun |
| 著者所属（英） | NASA Johnson Space Center |
| 発行日 | 2007-08-13 |
| 言語 | eng |
| 内容記述 | The Zagami basaltic shergottite has fine- and coarse-grained (FG & CG) areas, which may reflect partial crystallization in a deep, slowly cooled magma chamber to form Mg-rich pyroxene cores, followed by entrainment of these crystals into a magma that rose and crystallized near the surface. Late-stage melt pockets formed mesostasis and feldspar (maskelynite) having a range of compositions, but low water abundance. Higher I(sub Sr) in the FG portion may result from the second stage having incorporated old crustal rocks that failed to reach isotopic equilibrium. Zagami, like other shergottites, contains excess Ar-40(sub xs) beyond that expected from internal decay of K-40 during its Sm-Nd age of 177 Myr. We suggest that at least a portion of this Ar-40(sub xs) in Zagami and some other shergottites was inherited from the magma, much as is the case of MORBs on Earth. We made Ar-39-Ar-40 age determinations on feldspar and pyroxene separates from both the FG and CG portions of Zagami. If Zagami experienced an evolving fractional crystallization history, including possible crustal contamination of the magma, that might be indicated in differing amounts of Ar-40(sub xs) between mineral phases and between FG and CG portions. |
| NASA分類 | Lunar and Planetary Science and Exploration |
| 権利 | No Copyright |
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