[S-CG58] 沈み込み帯へのインプットを探る：海溝海側で生じる過程の影響

[SCG58-03] プチスポット火山活動による沈み込むプレートの改変：CO₂に富むアセノスフィアメルトの付加

★招待講演

*町田 嗣樹¹、佐藤 勇輝²、平野 直人^2,3 (1.千葉工業大学　次世代海洋資源研究センター、2.東北大学大学院　理学研究科、3.東北大学　東北アジア研究センター)

キーワード：CO2に富む珪酸塩メルト、交代肥沃化作用、海洋リソスフィア、プチスポット

Petit-spot is the definitive evidence for partial melting in the asthenosphere caused by Carbon dioxide (CO₂) [1]. Recent our studies [1, 2, 3, 4] identified two types of eruption process of CO₂-rich silicate melt from asthenosphere due to petit-spot volcanism, which corresponds to differences of the stress field of oceanic lithosphere. On the concavely flexed region, CO₂-rich melt reacts [2] and equilibrates [1] with ambient peridotite in the lower lithosphere before eruption. In contrast, on the convexly flexed region, CO₂-rich melt erupts directly from the asthenosphere [3]. Our results [3, 4] suggest that majority of petit-spot volcanoes in the western North Pacific correspond to the former type of process. We thus consider that petit-spot volcanism provides insights into understanding the nature of pre-subduction modification of oceanic lithosphere.
In this presentation, we review geochemical and geochronological variation of petit-spot lava and xenocryst therein from the western North Pacific, to discuss reaction processes between CO₂-rich melt and oceanic lithosphere.



References
[1] Machida, et al. (2017) Nature Communications 8, 14302.
[2] Pilet, et al. (2016) Nature Geoscience 9, 898-903.
[3] Sato, et al. (2017) International Geology Review, doi: 10.1080/00206814.2017.1379912.
[4] Machida, et al. (2015) Earth and Planetary Science Letters 426, 267-279.