Tracing the subducting Pacific slab to the mantle transition zone with hydrogen isotopes

Takeshi Kuritani,Qun-Ke Xia,Eiichi Sato,Kenji Shimizu,Mitsuhiro Nakagawa,Takayuki Ushikubo,Jia Liu,Hajime Taniuchi,Nobuo Doi

doi:10.1038/s41598-021-98307-y

Abstract

Hydrogen isotopes have been widely used as powerful tracers to understand the origin of terrestrial water and the water circulation between the surface and the deep interior of the Earth. However, further quantitative understanding is hindered due to a lack of observations about the changes in D/H ratios of a slab during subduction. Here, we report hydrogen isotope data of olivine-hosted melt inclusions from active volcanoes with variable depths (90‒550 km) to the subducting Pacific slab. The results show that the D/H ratio of the slab fluid at the volcanic front is lower than that of the slab fluid just behind the volcanic front. This demonstrates that fluids with different D/H ratios were released from the crust and the underlying peridotite portions of the slab around the volcanic front. The results also show that the D/H ratios of slab fluids do not change significantly with slab depths from 300 to 550 km, which demonstrates that slab dehydration did not occur significantly beyond the arc. Our estimated δD‰ value for the slab materials that accumulated in the mantle transition zone is > − 90‰, a value which is significantly higher than previous estimates.

Highlights

Hydrogen isotopes have been widely used as powerful tracers to understand the origin of terrestrial water and the water circulation between the surface and the deep interior of the Earth
Little is understood about the changes in the decrease the hydrogen isotope (D/H) ratio of subducting slabs with increasing depth, which is a key issue in estimating the characteristic D/H ratios of subducted recycled materials in the deep mantle reservoir
To trace the evolution of the D/H ratios of the subducting Pacific slab from the volcanic front to the mantle transition zone (MTZ), the hydrogen isotopic compositions of olivine-hosted melt inclusions were determined for basaltic scoria samples from six active volcanoes, including Iwate (Z = ~ 90 km), AkitaKomagatake (Z = ~ 100 km), Me-Akan (Z = ~ 110 km), Oshima-Oshima (Z = ~ 180 km), Rishiri (Z = ~ 300 km), and Fukue (Z = ~ 550 km) (Fig. 1)

Summary

Introduction

Using the results of hydrogen isotopic analyses on olivine-hosted melt inclusions for some Mariana arc volcanoes, Shaw et al.[9] estimated the δD‰ values (δD‰ = [(D/H)Sample − (D/H)SMOW]/(D/H)SMOW × 1000, where SMOW refers to the standard mean ocean water, and δD = 0‰) of the subducted materials after 92% d ehydration[14] to be as low as − 234‰.

Results

Conclusion