Transition of magmatic composition reflecting an evolution of rifting activity. A case study of the Akita-Yamagata basin in Early to Middle Miocene, Northeast Honshu, Japan.

Evolution of late Cenozoic magmatism and the crust–mantle structure in the NE Japan Arc

“…Continental margin volcanism first occurred at c. 35 Ma in the western continental rift zone (Kano et al 2007), and volcanism during this stage was dominated by subaerial andesite activity. Back-arc basin volcanism was active in the Yamato Basin between 21 and 17 Ma (Kaneoka et al 1992), followed by rift volcanism in the Aosawa Rift at 17 -15 Ma (Yagi et al 2001), and in the Kuroko Rift at 15-13.5 Ma (Yamada & Yoshida 2011).…”

“…The first half of the back-arc basin period was characterized by the effusion of large amounts of seafloor basalt during the opening of the Yamato Basin, whereas the second half was characterized by spatially varying amounts of graben-fill basalt and rhyolite effusions, as part of the bimodal volcanism in the Northern Honshu rift (Yagi et al 2001;Yamada & Yoshida 2011). Rhyolitic magmas are mainly distributed in the forearc side, which is underlain by the inland continental margin crust (Fig.…”

“…20b: Yoshida et al 1995). (Kurasawa & Konda 1986); the eastern margin of the Japan Sea (Aosawa rift) at 16.5 Ma (Ujike & Tsuchiya 1993;Yagi et al 2001); and the inland NE Japan (Kuroko rift) at 15 Ma (Yagi et al 2001;Nohda 2009;Yamada et al 2012). Nohda (2009) explained this relationship by an eastward asthenospheric flow during the continental arc to the back-arc basin periods (Fig.…”

“…The discrimination fields are from Meschede (1986), and the N-MORB source is from Wood et al (1979). Additional data are from Allan & Gorton (1992), Shuto et al (1995) and Yagi et al (2001). Yamada et al (2012) calculated the evolution of the Zr -Nb -Y composition of basalt melts during the adiabatic ascent of a primitive mantle (PM: Sun & McDonough 1989) and a depleted mantle (DM: Workman & Hart 2005) source.…”

“…The Northern Honshu rift is younger (Middle Miocene), and formed a deep sedimentary basin by simple shear. Basalts were erupted along the rift axis associated with a thinning of the upper crust (Yagi et al 2001;Sato et al 2004). Very active felsic volcanism, which created more than 80 calderas concentrated along the topographic high of the Ou Backbone range (Ito et al 1989;Sato & Yoshida 1993;Sato 1994;Yoshida et al 1999a), occurred at the main stage of the island-arc period in NE Honshu (Fig.…”