Mélange diapir origin for Neo-Tethyan ridge-subduction magmatism

The mélange diapir model invokes physical mixing of partially melted slab components with mantle wedge peridotite, enabling material transfer from the subducted slab to the overlying mantle wedge. However, identifying distinctive igneous rock suites generated through this process in hot ridge-subduction settings remains equivocal. In this study, we identified a Late Cretaceous (ca. 87−82 Ma) high-Si adakite, Nb-enriched gabbro, and arc magmatic suite in southern Sumatra, Indonesia. Combined elemental data and multiple Sr-Nd-Pb-Hf-O-Mg isotopes indicate that the mafic-intermediate igneous rocks are calc-alkaline, whereas the gabbro/gabbro diorite samples have relatively high Nb contents and were derived from the bulk mixing of depleted mid-ocean-ridge basalt mantle and subducted sediment, with subducted bulk peridotites serving as the magma source region. The high-Si adakites belong to the high-K calc-alkaline series and were generated by partial melting of newly underplated juvenile mafic rocks, which were derived from the coeval mafic magma. The magmatic suite formed in response to the Neo-Tethyan Wharton Ridge subduction during the Late Cretaceous. Our results suggest that the mélange diapir model is a possible mechanism for generating distinctive igneous rock suites and transporting slab materials during ridge subduction.