Abstract
Ca,Mg-sulfates are subduction-related sources of oxidized S-rich fluid under lithospheric mantle P,T-parameters. Experimental study, aimed at the modeling of scenarios of S-rich fluid generation as a result of desulfation and subsequent sulfide formation, was performed using a multi-anvil high-pressure apparatus. Experiments were carried out in the Fe,Ni-olivine–anhydrite–C and Fe,Ni-olivine–Mg-sulfate–C systems (P = 6.3 GPa, T of 1050 and 1450 °C, t = 23–60 h). At 1050 °C, the interaction in the olivine–anhydrite–C system leads to the formation of olivine + diopside + pyrrhotite assemblage and at 1450 °C leads to the generation of immiscible silicate-oxide and sulfide melts. Desulfation of this system results in the formation of S-rich reduced fluid via the reaction olivine + anhydrite + C → diopside + S + CO2. This fluid is found to be a medium for the recrystallization of olivine, extraction of Fe and Ni, and subsequent crystallization of Fe,Ni-sulfides (i.e., olivine sulfidation). At 1450 °C in the Ca-free system, the generation of carbonate-silicate and Fe,Ni-sulfide melts occurs. Formation of the carbonate component of the melt occurs via the reaction Mg-sulfate + C → magnesite + S. It is experimentally shown that the olivine-sulfate interaction can result in mantle sulfide formation and generation of potential mantle metasomatic agents—S- and CO2-dominated fluids, silicate-oxide melt, or carbonate-silicate melt.
Highlights
Sulfur, hydrogen, oxygen, and carbon are the major magmatic volatiles in the Earth’s mantle and crust
Being a redox-sensitive element, sulfur can exist in reduced form (S2− or S) as sulfides or native sulfur, sulfide melts or reduced fluid, intermediate form (S4+ ) as an SO2 -component of erupted melts and in oxidized form (S6+ ) as sulfates, oxidized fluids, or dissolved in silicate melts [1,2,3,4,5]
Results of the present study demonstrate that the interaction of Ca,Mg-sulfates with Fe,Ni-bearing forsterite can be considered as a simplified model of these processes occurring during the subduction of oxidized crustal material into silicate mantle
Summary
Hydrogen, oxygen, and carbon are the major magmatic volatiles in the Earth’s mantle and crust. Subduction processes play a key role in the transport of S in deep zones of the. Existing data demonstrate that only 15–30% of sulfur, transported into the mantle with a subducted slab is released to the atmosphere via magmatic degassing at arcs [7]. Most of the sulfur, which is retained in the down-going slab, either interacts with upper mantle rocks or is recycled to the deep mantle. The heterogeneity of the Earth’s mantle as well as redox- and compositional contrast of slab and lithospheric mantle rocks results in numerous scenarios of sulfur behavior in the course of the subduction processes
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