Abstract:

Songduo eclogites within the Tibetan regions are typical products of subduction of ancient oceanic crust, and thus studied in details in this paper. Petrographic observations and thermodynamic calculation confirm that the Songduo eclogites have experienced reduction reaction during the oceanic subdution. Fe3+ and S6+ were reduced to Fe2+ and S2- , respectively, releasing the fluids enriched in CO2 and H2S in the subduction channel. The CO2 and H2S-rich fluids were subsequently transferred into the overlying mantle wedge, and partially released into the atmosphere through the arc volcanoes. Therefore, it is regarded that the currently deep subduction of India oceanic crust experienced similar reduction reactions in deep earth. The sulfur is liberated from the buried surface
sulphates into the sulfur-bearing fluids, and released into the atmosphere through the Tambora-like volcanoes. Today, the oceanic subduction and reduction reactions continued, and then, the newly-formed sulfur-bearing fluids continuously sunk in the magma chambers beneath the island arc volcanoes. Therefore, the tambora-like volcanic eruption is a high probability event happening in the near future.