Lunar volcanism was pervasive, producing mare lava flows and associated features such as sinuous rilles, pyroclastic deposits and domes. The magmas that made these features were basalts - melted mantle rocks rich in silica, oxygen, iron and magnesium. The latter two elements give basalts the dark color we see in the maria. Lunar scientists have hunted for other types of volcanic rocks, and these two domes near the crater Gruithuisen are the best known examples. Gruithuisen Gamma is about 20 km wide and 1200 m high; Gruithuisen Delta is 13 km wide and 1550 m high. Their steep sides suggest they were formed by more viscous lavas than normal mare domes such as those near Cauchy and Hortensius. Mathematical models of dome growth reaffirm this idea. On Earth, lavas with similar flow characteristics to the Gruithuisen domes are rhyolites, dacites and basaltic andesites - rocks with more silica and less iron and magnesium than basalts. If these lunar domes are made of silica-rich magma the next question is why?
Technical Details:
Date: 13th Feb, 2003 15:22UT; Moon 13 days old. Takahashi Mewlon 250 (250mm F/12 Dall Kirkham) at
f/27, mounted on a William Optics GT-1. Philips PCVC740K ToUcam Pro used with Televue 2X Barlow.
Related Links:
H-R Lunar and Planetary Images from Singapore
Lunar Gruithuisen and Mairan domes: Rheology and mode of emplacement
Lunar Orbiter IV view
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