Geology of Ascension Island other volcanic islands, which only have a few mafic and felsic endmembers such as basalt or rhyolite, Ascension has a full-range from some of the most mafic to most felsic. This includes basalt, hawaiite, mugearite, benmoreite,trachyte and rhyolite. Potassium-argon dating indicates that the oldest rocks exposed above the water are one million year old rhyolites. Geologists have divided the island's mafic and felsic rocks into different named sequences and sub-divided mafic rocks based on their ratio of zirconium and niobium. The Sister's Peak region in northwest Ascension has intermediate mafic lava flows, scoria cones and mafic ash fall deposits near
Granite This leads to significant extraction of hydrous felsic melts from granulite-facies resitites. A-type granites occur in the Koettlitz Glacier Alkaline Province in the Royal Society Range, Antarctica. The rhyolites of the Yellowstone Caldera are examples of volcanic equivalents of A-type granite. H-type granites were suggested for hybrid granites, which were hypothesized to form by mixing between mafic and felsic from different sources, e.g. M-type and S-type. However, the big difference in rheology between mafic and felsic magmas makes this process hardly happening in nature. An old, and largely discounted process, granitization states that granite is formed in place through extreme