Time-progressive mantle-melt evolution and magma production in a Tethyan marginal sea: A case study of the Albanide-Hellenide ophiolites

We present a comprehensive overview of the melt evolution of the upper mantle peridotites and different lava types occurring in the Jurassic Albanide-Hellenide ophiolites, based on new and extant geochemical data and trace element modeling. Peridotites consist of lherzolites and harzburgites that are variably depleted, and show increasing light rare earth element (LREE) enrichment with increasing whole-rock depletion. The spatial-temporal relationships of volcanic rocks indicate four discrete types with progressively younging ages: (1) normal mid-oceanic ridge basalts (N-MORBs); (2) medium-Ti basalts (MTBs); (3) island arc tholeiitic (IAT) basalts; (4) boninitic rocks. Our REE modeling reveals the following results. (1) Moderately depleted lherzolites represent N-MORB mantle residua produced by 10%-20% partial melting of a depleted MORB mantle source. Melt extraction formed N-MORB lavas. (2) Residual lherzolite underwent 5%-8% partial melting without any subduction influence, producing MTB magmas. (3) Following subduction initiation, these refractory lherzolites were enriched in LREEs by subduction-derived fluids. Their partial melting (similar to 10%-20%) generated IAT magmas. (4) With continued subduction, the highly depleted residual mantle left after the previous melting events underwent significant LREE enrichment and high degree (15%-25%) partial melting, producing the youngest, boninitic rocks. The residual mantle after boninitic melt extraction is represented by extremely refractory harzburgites. This progressive melt evolution of the upper mantle peridotites and volcanic rock types is compatible with that of the subduction initiation-related magmatism and mantle dynamics in the Izu-Bonin-Mariana arc-trench rollback system, and indicates a time-progressive mantle-melt evolution in the upper plate of the Tethyan subduction system.