Iron redox and hydrogen generation during multistage serpentinization under low silica activity: insights from the Heimulin serpentinites, central China - Meijun Gong; Kai Wu; Xinru Zhu; Chang Zhang; Chao Zhang; Hong Zhang; Yang Hu; Juan Zhang; Honglin Yuan; Weidong Sun (Geochimica et Cosmochimica Acta, 2026)