Sediment‐enriched adakitic magmas from the Daisen volcanic field, Southwest Japan

Abstract

[1] The Quaternary Southwest Japan Arc is a product of subduction of the hot, young Philippine Sea Plate beneath the Eurasian Continental Plate. The magmas erupted from the Southwest Japan Arc belong to a category of magmas commonly referred to as ''adakites'' or ''adakitic magmas''. These magmas show trace element evidence for interaction with garnet at depth, and may be associated with partial melting of subducted altered oceanic crust. Also found throughout the southern Sea of Japan region are alkali basalts with little apparent connection to the subduction zone. We have determined major element, trace element, and Sr, Nd, Pb, and U-Th isotopic compositions for a bimodal suite of lavas erupted at the Daisen volcanic field in the Southwest Japan Arc. These magmas consist of mildly alkaline basalts and a calcalkaline intermediate suite, separated by a $10 wt.% silica gap. The intermediate magmas show trace element and isotopic evidence for interaction with garnet, consistent with partial melting of the hot, young ($20 Ma) Philippine Sea Plate. The Daisen intermediate magmas are distinct from other adakitic magmas in their radiogenic isotopic characteristics, consistent with a significant contribution ($25%) from subducted Nankai Trough sediments. Our data suggest that the basalts erupted at the Daisen volcanic field are not parental to the intermediate magmas, and contain a small contribution of EM1-like mantle common in Sea of Japan alkali basalts but not apparent in the Daisen intermediate magmas.

Comment on “Diverse magmatic effects of subducting a hot slab in SWJapan: Results from forward modeling” by J.‐I. Kimura et al.

“…This conclusion differs from that of an earlier study by Feineman et al . [], who advocated only a minimal crustal effect and concluded that the Pb isotope array for Daisen ADK can be attributed to partial melting of the subducting slab with a significant amount of sediment. The Pb isotope trends for Daisen ADK presented in these two studies are clearly different (Figure ) and Kimura et al .…”

“…(c and d) Comparison of data sets for Daisen ADK. Compositions of upper crustal (UC) [ Feineman et al ., ] and lower crustal (LC) [ Moriyama , ] lithologies are shown in the insets. The “X” indicates the hypothetical crustal component suggested by Kimura et al .…”

“… Pb isotope composition of ADK from Daisen and Aonoyama, obtained by Feineman et al . [], and this study, in comparison with those obtained by Kimura et al . [].…”

“…Data sets in Feineman et al . [] and obtained in this study show a trend shallower than that produced by the data in Kimura et al . [].…”

Diverse magmatic effects of subducting a hot slab in SW Japan: Results from forward modeling

“…Many models have been proposed for magma genesis in the SW Japan arc. The models include an enriched lithospheric mantle origin of OIB [ Hoang and Uto , ; Kakubuchi et al ., ], aqueous fluid‐fluxed mantle melting for AB [ Iwamori , ], carbonaceous melt‐fluxed melting for Miocene OIB [ Tatsumi et al ., ], hydrous shallow mantle melting with residual phlogopite for SHO [ Tatsumi and Koyaguchi , ], slab melt‐fluxed mantle melting for HMA [ Kimura et al ., ; Shimoda et al ., ; Tatsumi and Hanyu , ], slab melting for ADK [ Feineman et al ., ; Kimura et al ., ; Morris , ], remelting of solidified andesite for ADK [ Tamura et al ., ], and deep garnet fractionation of hydrous basalt for ADK [ Zellmer et al ., ].…”