Seamount subduction and its role in triggering magmatic flare-ups: Evidence from the Late Devonian Northern Yili Arc

Magmatic flare-ups are widely recognized as pivotal features of continental arc magmatism, yet their driving mechanisms remain poorly understood. In this study, we present new radiometric ages and geochemical data for normal calc-alkaline, high-magnesian, and Nb-enriched arc magmatic rocks from the Northern Yili Arc (Western Tianshan, China), which coincide with the Late Devonian magmatic flare-up in the region. The normal arc magmatic rocks likely originated from partial melting of a slab fluid-metasomatized mantle wedge, possibly accompanied by fractional crystallization and crustal assimilation processes. In contrast, the high-magnesian andesites (HMAs) and Nb-enriched basalts (NEBs) were derived from sediment melt and slab melt-metasomatized mantle sources, respectively. The systematic decoupling of Nd-Hf isotopes in contemporaneous mafic-intermediate lavas further indicates mantle source heterogeneity. The clustered eruption of HMAs and NEBs, alongside enriched continental signatures in their mantle sources, implies intensified slab-mantle interactions. We attribute this to enhanced interaction efficiency driven by a unique geodynamic process. We propose that the most plausible mechanism for the Late Devonian−Early Carboniferous magmatic fluctuations involves seamount/oceanic plateau subduction followed by slab retreat or rollback. The Late Devonian seamount subduction scenario provides new insights into the geodynamic evolution of the North Tianshan Ocean, the distribution of Au-Cu deposits, and the polarity of subduction in ancient oceanic plates within the Yili microcontinent.