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
Archean felsic volcanic rocks rocks in Archean greenstone belts is between dacite to rhyolite (Table 2). In comparison, the modern felsic volcanic rock average composition (after Archean, <2.5 Ga) is similar to rhyolite, indicating a more felsic shift in felsic volcanism. However, the composition may be biased because of weathering right after deposition or metamorphism during later stages of deformation. In addition, Archean felsic volcanic rocks have high zircon abundance. Incompatible elements, like zirconium, are reluctant to substitute into early-forming crystals. So, they tend to remain in the melt. In strongly fractionated felsic magma, zircon is easily saturated. As a result, zircon is common