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Geochemical variations of the Quaternary Daisen adakites, Southwest Japan, controlled by magma production rate

2019; Elsevier BV; Volume: 350-351; Linguagem: Inglês

10.1016/j.lithos.2019.105214

1872-6143

Takahiro Yamamoto, Nguyễn Hoàng,

High-pressure geophysics and materials

The late Cenozoic Southwest Japan arc was formed by hot subduction of the young Shikoku Basin slab, and Daisen Volcano has erupted exclusively adakitic products since ca.1.0 Ma under this subduction regime. Although previous studies have revealed that the adakites of this arc were generated by melting of the subducted basaltic crust and incorporation of slab sediments, this model cannot simply explain the observed geochemical variations of the Daisen adakites. We determined chronological variations in the major and trace element and Sr-Nd-Pb isotopic compositions of the Younger stage products of Daisen (<210 ka) based on a newly reported stratigraphy. Our result shows that the Daisen adakites are divided into higher-K and lower-K groups; the former having higher in TiO2, Sr, Ba, Nb and La contents and more depleted in Sr-Nd-Pb isotopic compositions than the latter. Mass balance estimation suggests that the lower-K adakites represent a higher degree of lower crustal assimilation than the higher-K adakites. Furthermore, the lower-K adakites erupted during a period of increased eruptive activity (100–27.8 ka), whereas the higher-K adakites were erupted before and after that period. We attribute this correlation to an increased degree of lower crustal assimilation resulting from an increased rate of magma intrusion into the crust during the period of increased activity. Following this flare-up period, the eruption rate and degree of assimilation declined, and eruptive activity ceased at 20.8 ka.