Abstract
Mantle plume-related magmas typically have higher chalcophile and siderophile element (CSE) contents than mid-ocean ridge basalts (MORB). These differences are often attributed to sulfide-under-saturation of plume-related melts. However, because of eruption-related degassing of sulfur (S) and the compositional, pressure, temperature and redox effects on S-solubility, understanding the magmatic behavior of S is challenging. Using CSE data for oceanic plateau basalts (OPB), which rarely degas S, we show that many OPB are sulfide-saturated. Differences in the timing of sulfide-saturation between individual OPB suites can be explained by pressure effects on sulfur solubility associated with ascent through over-thickened crust. Importantly, where S-degassing does occur, OPB have higher CSE contents than S-undegassed melts at similar stages of differentiation. This can be explained by resorption of earlier-formed sulfides, which might play an important role in enriching degassed melts in sulfide-compatible CSE and potentially contributes to anomalous enrichments of CSE in the crust.
Highlights
Mantle plume-related magmas typically have higher chalcophile and siderophile element (CSE) contents than mid-ocean ridge basalts (MORB)
There is general consensus that oceanic plateau basalts (OPB) are generated by higher degrees of partial melting (~30%; ref. 24) and fractionate at pressures equal to or greater than MORB25–27
Primitive OPB are offset to slightly higher [FeOT] at a given [MgO] compared to MORB, which is consistent with the expected partial melting trajectory[28]
Summary
Mantle plume-related magmas typically have higher chalcophile and siderophile element (CSE) contents than mid-ocean ridge basalts (MORB). These differences are often attributed to sulfide-under-saturation of plume-related melts. Where S-degassing does occur, OPB have higher CSE contents than S-undegassed melts at similar stages of differentiation. Sulfur solubility is sensitive to processes such as magma cooling, fractional crystallization, magma ascent, magma chamber recharge and crustal contamination Complex processes, such as sulfide formation and later dissolution during ascent, might occur during crustal differentiation. They are considered to be derived from relatively short-lived mantle plumes[18,19] Despite differences in their formation, the major and trace element systematics and fO2 of oceanic plateau basalts (OPB) and MORB are similar[20]. These aspects of OPB chemistry, coupled with clear differences in crustal thickness (up to 30 km; ref. 21) relative to the oceanic crust (~6.5 km; ref. 22)
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