Sulfide is a ubiquitous phase in the mantle (Alard et al., 2011) and an important repository for sulfur and geochemically and economically important chalcophile metals, which plays a pivotal role in the partitioning behaviors of PGE, Cu, and Ni (Mungall & Brenan, 2014;Patten et al., 2013). Understanding the factors that control the fate of sulfide phases in the partially molten mantle is of fundamental importance in exploring the recycling of sulfur and chalcophile elements among different geochemical reservoirs (
Extraction of sulfides from the partially molten mantle is vital to
elucidate the cycling of metal and sulfur elements between different
geochemical circles but has not been investigated systematically. Using
laboratory experiments and theoretical calculations, this study
documents systematical variations in lithologies and compositions of
silicate minerals and melts, which are approximately consistent with the
results of the thermodynamically-constrained model. During a
melt-peridotite reaction, the dissolution of olivine and precipitation
of new orthopyroxene generate an orthopyroxene-rich layer between the
melt source and peridotite. With increasing reaction degree, more melt
is infiltrated into and reacts with upper peridotite, which potentially
enhances the concomitant upward transport of dense sulfide droplets.
Theoretical analyses suggest an energetically focused melt flow with a
high velocity (~ 170.9 μm/h) around sulfide droplets
through the pore throat. In this energic melt flow, we, for the first
time, observed the mechanical coalescence of sulfide droplets, and the
associated drag force was likely driving upward entrainment of fine
μm-scale sulfide. For coarse sulfide droplets whose sizes are larger
than the pore throat in the peridotite, their entrainment through narrow
constrictions in crystal framework seems to be physically possible only
when high-degree melt-peridotite reaction drives high porosity of
peridotite and channelized melt flows with extremely high velocity.
Hence, the melt-rock reaction could drive and enhance upward entrainment
of μm- to mm-scale sulfide in the partially molten mantle, potentially
contributing to the fertilization of the sub-continental lithospheric
mantle and the endowment of metal-bearing sulfide for the formation of
magmatic sulfide deposits.
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