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
Eoarchean geology highly deformed biotite-hornblende tonalitic to granitic orthogneiss. Subordinate mafic amphibolitic and chloritic elliptical enclaves and inclusions are observed in felsic gneisses.Although the rocks are highly deformed and could not reflect the original field relation between rock units, the chemical composition of the rocks showcases how Eoarchean greenstone-TTG be like. Chemical composition in the mafic inclusion suggests the acasta area was possibly a supra-subduction setting. Dominant felsic rocks are composed of highly deformed tonalitic, granodioritic and granitic gneisses. Inclusion of as early as 4.2 billion years old zircon core are observed in the gneisses. Mafic rocks, i.e. subordinate amphibolite and ultra