There is some thought that decompression melting could generate silica rich melts from mafic sources. Recent (relatively) work on the Long Valley Caldera system shows that decompression melting is responsible for most of the large volume volcanics from it's eruptions. The decompression melting there related to structural "pull-apart". I don't know to what extent this process can be expanded to the massive mid-tertary ignibrite flare-up because it predates most of the B&R extension, but that puzzle has perplexed me since I first learned of it when I started doing minerals exploration in the early 1980's.
Thanks for this. Yes, I think the ultimate cause of all that Tertiary volcanism (and its felsic/granitic/rhyolitic nature) is certainly not simple or straightforward.
There is some thought that decompression melting could generate silica rich melts from mafic sources. Recent (relatively) work on the Long Valley Caldera system shows that decompression melting is responsible for most of the large volume volcanics from it's eruptions. The decompression melting there related to structural "pull-apart". I don't know to what extent this process can be expanded to the massive mid-tertary ignibrite flare-up because it predates most of the B&R extension, but that puzzle has perplexed me since I first learned of it when I started doing minerals exploration in the early 1980's.
Thanks for this. Yes, I think the ultimate cause of all that Tertiary volcanism (and its felsic/granitic/rhyolitic nature) is certainly not simple or straightforward.