Modification of Lithospheric Mantle by Melts/Fluids With Different Sulfur Fugacities During the Wilson Cycle: Insights From Lesvos and Global Ophiolitic Peridotites

Abstract

AbstractThe Lesvos ophiolite, Greece, was recently identified as an analog to the External Liguride Unit formed at an ocean‐continent‐transition (OCT) setting. To further study the evolutionary history of this body, we analyzed highly siderophile element abundances and Re‐Os isotopic compositions of 14 Lesvos peridotites, in combination with petrology, bulk‐rock major, and trace element geochemistry. Almost all the Lesvos peridotites fall within the field of global OCT and mid‐ocean‐ridge (MOR) peridotites, indicating that these rocks have not experienced subduction‐related processes. The near‐horizontal 187Os/188Os versus Al2O3 trend over a wide range of Al2O3 (0.45–3.66 wt. %) may have been caused by recent melt depletion during rifting and thinning of the Lesvos lithosphere. Combining data from available global ophiolitic peridotites, we find that a large proportion of the more Al‐depleted supra‐subduction‐zone (SSZ) peridotites show lower Os/Ir, higher Pd/Ir and remarkably elevated radiogenic Os relative to other tectonic environments (OCT and MOR). By linking this kind of geochemical evolution to the Wilson Cycle, a complete picture emerges: (a) In the OCT to MOR stages, the extensional rifting environment may lead to mild to moderate melt depletion, followed by, or associated with, infiltration of S‐saturated (high fS2) basaltic magmas; (b) when progressing into the SSZ stage, more extreme degrees of mantle melt depletion may be driven by aqueous fluids in the sub‐arc mantle. During this stage, high‐fO2 slab‐derived fluids and/or S‐undersaturated (low fS2) boninitic magmas may infiltrate the sub‐arc mantle, followed by subsequent S‐saturated forearc basaltic magma infiltration.