Sulfur Isotope Heterogeneity of Eclogites and the Scales of Fluid Mass-Transfer in the Root Zones of Subduction-Collision Orogens (North Muya Block, Northeastern Transbaikalia)

Abstract—Variably retrogressed eclogites and amphibolites from the North Muya block (Eastern Siberia) bear disseminated pyrite + chalcopyrite ± pyrrhotite mineralization of metasomatic origin. Fluid metasomatism led to the precipitation of pyrite with contrasting δ34S signatures (from −10 to +9‰) produced by oxidized ( SO₄^2 - ) or reduced (H2S or HS−) sulfur from a fluid. The data indicate contrasting sulfur reservoirs in the deep orogenic lithosphere, which were controlled by devolatilization of variably oxidized metasediments.