Evolution of the Earth as an andesite planet: water, plate tectonics, and delamination of anti-continent

The Earth is unique in our solar system in having a buoyant, highland-forming continental crust with a differentiated, andesitic composition; thus, it can be referred to as an “andesite planet.” Andesitic magmatism is associated with convergent plate margins such as subduction zones, leading to a broad consensus that this setting has been the major site of continental crust formation. However, while andesites are dominant in mature continental arcs, they are subordinate in juvenile oceanic arcs, resulting in a great conflict regarding the creation of the continental crust. We focused on the Izu-Bonin-Mariana arc to assess this problem, as it is a juvenile intra-oceanic arc with a mid-crustal layer that has a seismic velocity identical to that of the bulk continental crust. Petrological modeling of the production of andesitic melts by the mixing of mantle-derived basalt with crust-derived, rhyolite magmas successfully reproduced the crust/mantle structure observed in seismic profiles of the Izu-Bonin-Mariana arc. As a result, we presented a challenging hypothesis: the continent was created in the ocean. One key mechanism that differentiates initial basaltic arc crust to evolved, andesitic continental crust may be the delamination of SiO 2 -depleted residues of crustal melting, termed “anti-continent,” from the arc crust.