Other
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...p21a09n&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #P21A-09
Other
1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 3670 Minor And Trace Element Composition, 5430 Interiors (8147), 5455 Origin And Evolution, 5480 Volcanism (8450)
Scientific paper
Recent remotely sensed data from the orbiting Lunar Prospector spacecraft has demonstrated the existence of a Th-rich region or hotspot that encompasses the Apollo 14 landing site, as well as the existence of a small (340 +/- 90 km diameter) metallic core. The new data has prompted a reexamination of the Apollo samples to investigate the nature of the lunar interior. Data is presented that demonstrate the presence of garnet in the deep lunar interior (below ~500 km); Zr/Y and Sm/Yb ratios in some lunar picritic glasses are elevated above the levels in the crystalline basalts and KREEP. The glasses are reported by some authors to be derived from greater depths than the basalts, depths that would be consistent with the presence of garnet in the source. Siderophile element data, albeit sparse, suggest that the picritic glass source is enriched in these elements relative to the majority of basalts. We suggest that the glasses were derived from a garnet-bearing region of the Moon that escaped the Lunar Magma Ocean (LMO) melting event. In relating these conclusions to the lunar "hotspot", we have analyzed Apollo 12 mare basalts and one from Apollo 14 for the platinum-group elements (PGEs). The Apollo 12 landing site, while close to Apollo 14, is outside the Th-rich hotspot. Major and trace element and isotope data demonstrate the involvement of KREEP in the petrogenesis of Apollo 14 mare basalts. Apollo 14 basalt 14072 and Apollo 12 basalt 12038 contain elevated PGE abundances. If analyses of other Apollo 14 basalts confirm this PGE-enriched signature for the plume, did it originate in the lower (PGE-rich) mantle or is KREEP enriched in the PGEs? Has the garnet signature been swamped by the incorporation of KREEP that has been mixed in during the rise of the plume? We conclude that: 1) 12038 is related to the Apollo 14 basalts and was transported to the Apollo 12 site via meteorite impact; 2) The Th-rich hotspot represents a surfacing plume of KREEP-rich material; 3) The Th-rich hotspot originated due to overturn of the LMO cumulate pile that dragged KREEP components into the lunar interior. We use the returned samples to investigate the nature of the plume source.
Ely J. C.
Jain J. C.
Neal Chris R.
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