Monday, August 24, 2015


During our stay at Yosemite, we explored the famed Tuolumne intrusive sequence. This is a more or less representative pluton in the Sierra Nevada that records the mixing and chemical processing of numerous pulses of magma in a single magma chamber. The sequence is a classic geologic field trip that runs right along the highway through the Tuolumne Meadows. It turns out magma mixing is a shockingly controversial subject in geology, but these outcrops show evidence that individual feldspar crystals were partially dissolved and re-precipitated as additional pulses of magma changed the local chemistry. As a result of various processes, such as melting the surrounding country rock and partially crystallizing out certain minerals, the later formations of the intrusive sequence are more felsic (higher SiO2 content and lower FeO and MgO2 contents) and have larger crystals. One famous formation in this sequence is the Half Dome granodiorite, which makes up Yosemite's iconic Half Dome. 

This culminates in the awesomely huge MEGACRYSTS of the Cathedral Peak granodiorite.

We also got some really great views of Tuolumne Meadows, a particularly pretty portion of Yosemite National Park.

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