[S-CG58] Investigation of inputs to subduction zones: Influence of tectonic processes on the incoming plate

[SCG58-03] Modification of the subducting plate by petit-spot volcanism: Impregnation of CO₂-rich melt from the asthenosphere

★Invited Papers

*Shiki Machida¹, Yuki Sato², Naoto Hirano^2,3 (1.Ocean Resources Research Center for Next Generation (ORCeNG), Chiba Institute of Technology, 2.Graduate School of Science, Tohoku University, 3.Center for Northeast Asian Studies (CNEAS), Tohoku University)

Keywords:CO2-rich silicate melt, metasomatic enrichment, oceanic lithosphere, petit-spot

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.