Half Dome Granodiorite

Half Dome Granodiorite is granodiorite (see also granite) found in a region on and near Half Dome, in Yosemite National Park, California, United States. The granodiorite forms part of the Tuolumne Intrusive Suite (aka Tuolumne Batholith), one of the four major intrusive suites within the Sierra Nevada.

What rocks comprise it

The granodiorite has large crystals of biotite, hornblende, and both feldspars — orthoclase and plagioclase. The space between crystals tends to be filled with quartz. The hornblende tends to have large, over 0.5 in (1.27 cm) rectangular crystals. The biotite forms hexagonal "blocks," up to 0.25 in (6.35 mm) across. A knife blade can peel the edges.

Sphene is found in Half Dome Granodiorite. The grains are honey-colored, and large at 0.25 in (6.35 mm) across,.^[1]

Half Dome Granodiorite traces to early Late Cretaceous. It age is between 85 to 83.4 (+/-1 to 2%) Ma, with average age of 84.1 Ma. It is younger than Sentinel granodiorite (88.4 Ma), and older than Cathedral Peak granite (83.7 Ma).^[2] Half Dome Granodiorite is the Valley's youngest plutonic rock,.^[3]

Half Dome Granodiorite is the most common Yosemite Valley rock, east of Royal Arches and Glacier Point,.^[3]

Half Dome Granodiorite is the innermost major unit of the Tuolumne Intrusive Suite.

^ Glazner, Allen F, Stock, Greg M. (2010). Geology Underfoot in Yosemite. Mountain Press, p. 50. ISBN 978-0-87842-568-6.
^ Evernden, J.F., Curtis, G.H., and Lipson, J. (1957). "Geologic Unit: Half Dome". Retrieved 7 May 2016.{{cite web}}: CS1 maint: multiple names: authors list (link)
^ ^a ^b N. King Huber (1987). "The Geologic Story of Yosemite National Park". Retrieved 9 May 2016.

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