| Budget Amount *help |
¥3,770,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥270,000)
Fiscal Year 2007: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2006: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2005: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
Most studies of lunar rocks and soils have been conducted on samples collected by the Apollo and Luna missions, but these represent samples from near-equatorial regions of the near side of the Moon. However, recent discoveries of lunar meteorites, which have been blasted off the Moon only to land in the hot desserts and Antarctic ice fields of Earth, have provided great impetus to lunar science. These meteorites provide potentially new insights into the petrologic history of unexplored regions of the Moon, including some as distant as the far-side. In spite of their scientific value, chronological studies of lunar meteorites have been difficult, since most of them are complex breccias, and in some cases, their radiometric "clocks" typically have been disturbed by subsequent impact events.
In order to better understand the petrogenetic history of lunar meteorites, we have developed in-situ U-Pb age dating of phosphates grains using Sensitive High-Resolution Ion MicroProbe (SHRIMP) instal
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led at Hiroshima University. Our in-situ U-Pb dating method has been successfully applied to the lunar basaltic meteorites and has enabled us to unravel the thermal evolution of unexplored regions of the Moon, which spanned for more than a billion years, from 3.9 Ga to 2.9 Ga. The majority of known mare-basaltic meteorite have crystallization ages younger than ca. 3.9 Ga are consistent with those of Apollo and Luna collections and activity of mare basalt magmatism in the unexplored areas of the Moon inferred from the relative chronology based on recent remote-sensing studies, still matching to the hypothesis that mare volcanism occurred mainly after the late heavy bombardment that ended at 3.9 Ga.
One exception, Kalahari 009, which is classified into VLT basalt shows the oldest age of 4.35 Ga and the shortest exposure age of 220 yr, concluding that the Kalahari 009 represents our first sample from VLT-type cryptomaria on the Moon prior to the late heavy bombardment The ancient age of Kalahari 009 and its geochemical features appear compatible with the "active" mechanism model, and maybe a manifestation of a pre-Imbrium basin-forming event on the Moon. Less
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