H–O–B–Li isotope systematics for assessing slab-derived fluids: Importance of postdehydration processes
Year: 2025
Type: article
Abstract: In this study, the isotopic alteration of boron (B) and lithium (Li) in slab-derived fluids after they undergo dehydration processes is investigated using deep groundwater samples from the eastern Kii Peninsula of Japan. Isotopic and elemental analyses of hydrogen (H), oxygen (O), B, and Li reveal complex subsurface fluid mixing and geochemical interactions that exceed simple meteoric recharge. Three distinct groundwater groups were identified on the basis of δ 2 H–δ 18 O–Cl relationships: Group I has strong slab-derived water signatures, particularly along the Median Tectonic Line and near 34°50′N, with up to 60 % slab-derived contributions; Group II reflects mixing between meteoric water and ocean water; and Group III is predominantly meteoric. Spatial variations in δ 11 B and δ 7 Li isotopes suggest that local geochemical processes such as clay adsorption, silicate weathering, and igneous rock contributions significantly alter the original slab-derived isotopic signals. Rayleigh-type fractionation models explain the increased isotopic values in some wells, whereas low δ 11 B and δ 7 Li values elsewhere indicate localized sources. Notably, high Li values with low δ 7 Li values in the southwest indicate a Li supply from Miocene igneous intrusions beneath the Mesozoic accretionary complex. These findings highlight the need for an integrated multi-isotope approach to accurately trace fluid origins and reconstruct the geochemical pathways of slab-derived fluids in forearc groundwater systems.
Source: Applied Geochemistry
Authors: Rofiqul Umam, Ikuya Adachi, Tsutomu Yamanaka
Institution: University of Tsukuba
Language: English
Subfield: Geochemistry and Petrology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,490
Award: 水同位体データ基盤の時空間高分解能化と列島規模水循環解析
OpenAlex ID: W7117309632