The present study focused distributions of hydrogen and fluid-mobile elements including lithium isotopes in orogenic peridotites of the Horoman massif, Japan, to estimate spaciotemporal scales of mantle heterogeneity on light elements. The analytical results on the samples collected at various scales from kilometer (an entire massif) through meter (an outcrop) to submillimeter (a mineral) produced the following outcomes.
The Horoman peridotites were partly affected at 150 Ma by a subduction-zone fluid. However in the core of the massif, they have retained geochemical characteristics derived from sub-seafloor hydrothermal alteration at 1 Ga. The hydrogen abundances are more than 10-times higher than those of a typical residual mantle. The presence of the Horoman massif suggests that ancient oceanic mantle domains formed by sub-seafloor hydrothermal alteration could have survived in the mantle for at least 1 Gy, and have influenced to dynamics and chemical evolution of the mantle.