There are usually three opinions about the causes of andesite. According to the differentiation, it is believed that Andesite is a basaltic magma differentiation product. The main reason is that andesite is often symbiotic with basalt, and the initial values ​​of 87Sr/86Sr are similar. Asahi said that the Anshan rock is the result of the basaltic magma assimilation of the granitic continental crust. The main reason is that the Anshanite composition is between the basalt and the granite, and the andesite is mainly distributed in the continental crust. From the point of view of plate tectonics, the Anshan magma originated from the oceanic plate subducting beneath the continental plate, and the oceanic crust and its overlying sediments were affected by high temperature and high pressure, and transformed into amphibolite and quartz eclogite, and then partially melted. An andesite magma is formed; this magma rises into the mantle-shaped wedge-shaped area and can react with mantle rocks to form pyroxene rocks, which can be partially melted to form andesite magma; water in oceanic sediments and hydrated oceanic crust water in the subduction When it is deep, it rises out and rises to the overlying mantle wedge-shaped area, which makes the mantle rich in water, and the partial melting of the water-rich mantle can also form andesite. The experimental data show that the melting point of andesite is the lowest when the pressure is 3×109 Pa; and when it is 1~1.5×109 Pa, the enriched peridotite is partially melted to produce Anshan melt. The third cause of the genesis of andesite is now accepted by the majority.
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