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 (b) melting of felsic materials (e.g. TTG and/or sediments) formed younger potassium-rich GMS (see Table 3). They imply gradual chemical changes of the in the magma and the Earth's crust. Records of Archean felsic volcanic rocks shows a peculiar trend. The eruption of felsic volcanic rocks and plutonic activities in Archean are largely synchronised as show in overlapping zircon ages. On contrary, the chemical compositions of some felsic volcanic rocks are similar to that of GMS but they are much older than GMS. For example, a GMS-like rhyolite unit in the Abitibi Greenstone Belt (abnormally more enriched in potassium and