[S-GC38] 固体地球化学・惑星化学

[SGC38-P01] 海洋地殻のリサイクル年代：FOZO-HIMUタイプOIBからの制約

*下田 玄¹、小木曽 哲² (1.産業技術総合研究所地質調査総合センター、2.京都大学大学院人間・環境学研究科)

キーワード：HIMU、FOZO、リサイクリング年代

It is widely accepted that crustal materials were recycled back into Earth’s mantle via subduction zones (e.g., Hofmann and White, 1982; Zindler and Hart, 1986; Weaver, 1991; Stracke et al., 2005; Stracke et al., 2012). This process is considered to be a key role for the chemical evolution of the Earth because the process necessarily produced chemical heterogeneity in the mantle. One of most important constrains of the recycling process should be residence time of crustal material in the mantle (recycling age) which could be typically shown with timescale from formation of oceanic crust at a mid-ocean ridge to remelting of the crust in an uprising plume via deepest mantle. As the recycling ages can directly constrain timescale of mantle convection, substantial research effort has been conducted. However, conclusive estimate of the recycling ages has never been estimated. In order to estimate recycling ages of oceanic crusts, OIB with PREMA-FOZO-HIMU signature should be suitable because isotopic composition of these OIB were considered to be mainly affected with recycled pure oceanic crust and depleted MORB mantle (DMM (Shimoda and Kogiso, 2019). Therefore, isotopic compositions of these OIB can be explained with simple mixing between DMM and recycled oceanic crust. It may follow that there was no contribution of continental crustal materials in their source areas. Consequently, isotopic compositions of OIB with FOZO and HIMU signature should be “simplest system” in OIB, and thus suitable to estimate the recycling ages of oceanic crusts. In this paper, we will present new method to constrain recycling ages of oceanic crusts and discuss relationship between estimated recycling ages and geologic events.