Abstract
Interactions of mantle silicates with subducted carbonates, sulfides, and sulfur-rich fluids are experimentally simulated in the olivine-ankerite-sulfur and olivine-ankerite-pyrite systems using a multi-anvil high-pressure split-sphere apparatus at 6.3 GPa and range of 1050–1550 °C. Recrystallization of Fe,Ni-bearing olivine and ankerite in a sulfur melt was found to be accompanied by sulfidation of olivine and carbonate, involving partial extraction of metals, carbon, and oxygen into the melt, followed by the formation of pyrite (±pyrrhotite), diopside, and Fe-free carbonates. The main features of metasomatic alteration of Fe,Ni-olivine by a reduced sulfur fluid include: (i) a zonal structure of crystals (Fe-rich core, Mg-rich rim); (ii) inclusions of pyrite and pyrrhotite in olivine; (iii) certain Raman spectral characteristics of olivine. At T > 1350 °C, two immiscible melts, a predominantly sulfur melt with dissolved components (or a Fe–Ni–S–O melt) and a predominantly carbonate one, are generated. The redox interaction of these melts leads to the formation of metastable graphite (1350–1550 °C) and diamond growth (1550 °C). The studied olivine-ankerite-sulfur and olivine-ankerite-pyrite interactions may be considered as the basis for simulation of metasomatic processes accompanied by the formation of mantle sulfides during subduction of crustal material to the silicate mantle.
Highlights
Carbon and sulfur are some of the most common volatile components involved in mantle magmatic and metasomatic processes
Experimental study of the olivine-ankerite-sulfur interactions demonstrated that samples in relatively low-temperature experiments (T = 1050–1250 ◦ C, t = 60 h) were represented by an aggregate of coarse-crystalline olivine (0.1–1.0 mm) and pyrite
Our findings indicate that recrystallization of Fe,Ni-olivine and Fe-bearing carbonate and their sulfidation may occur in the presence of even a small amount of reduced S-bearing melt/fluid (±sulfide melt) at relatively low temperatures on the boundary between the “cold” slab and the mantle wedge
Summary
Carbon and sulfur are some of the most common volatile components involved in mantle magmatic and metasomatic processes. According to the modern data, subduction processes play a key role in the global carbon and sulfur cycles [1,2,3,4,5,6]. Subduction enables transport of crustal carbon-bearing material (carbonates and hydrocarbons) and sulfur (sulfides and sulfates) minerals to the mantle depths. Several studies [1,2,7] have assessed the amounts of carbon and sulfur brought to the mantle in subduction zones at an annual input of ~4.6 ± 4.0 × 1012 and ~2.5 ± 1.5 × 1012 moles, respectively. It is known that carbonate crustal material can be subducted to a depth of
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