Mercury isotope signatures in soils reveal degassing from fault zones on the eastern margin of the Tibetan Plateau

Abstract

Mercury isotopic fractionations in soils have been widely studied, but the mercury isotopic compositions in soils in earthquake fault zones are poorly understood. Here we investigated the fractionation characteristics of mercury isotopes in soils along the Anninghe-Zemuhe fault zone on the eastern margin of the Tibetan Plateau, Southwest China. The results showed that the δ²⁰²Hg values of soils ranged from −1.23‰ to 0.39‰ with an average of −0.86‰ ± 0.38‰, and the Δ¹⁹⁹Hg values ranged from −0.46‰ to −0.02‰ with an average of −0.27‰ ± 0.12‰ (1SD, n = 22). The Δ¹⁹⁹Hg values in deep soils were more negative than those in surface soils. The fault gouge had a more negative Δ¹⁹⁹Hg value and was different from the geological source with near-zero Δ¹⁹⁹Hg value. The characteristics of mercury isotope variations reveal that mercury-containing gas degasses from terrestrial and geological reservoirs in the Anninghe-Zemuhe fault zone. We demonstrate that mercury isotopes can reveal mercury sources from degassing in soils in active fault zones.