Geochemistry

Well-Aged Granite

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Science  03 Jul 2009:
Vol. 325, Issue 5936, pp. 13
DOI: 10.1126/science.325_13b

Granite is not unique to our planet. Granite-like rocks have been found, albeit comparatively rarely, on Mars, Venus, and the Moon and within meteorites. Terada and Bischoff report the age of a granite-like fragment found in a stony meteorite (Adzhi-Bogdo) that fell in Mongolia in 1949. Their analysis of the fragment using a high-resolution ion microprobe implies that its parental granite-like magma crystallized 4.53 billion years ago. Granites on Earth and the Moon crystallized at a later stage, making this fragment the earliest example of granite-like material in the solar system. Its age reveals that such material must have formed very early in the solar system's history. On Earth, granite formation is thought to require the presence of water and plate tectonics. This fragment, however, must have formed under dry conditions and without plate tectonics, calling for a different formation mechanism.

Astrophys. J. 699, L68 (2009).

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