Zoning texture and chemical composition of plagioclase recording magma recharge and mixing beneath Pako guyot in the West Pacific

Magma mixing results in chemical diversity and triggers eruptions, with these processes recorded in phenocryst textures. Previous research indicated that concurrent mixing and crystallization produced a mush rich in clinopyroxene beneath the Pako volcano of the Magellan seamount group in the West Pacific. However, it was insufficient to reconstruct the magma evolution history based solely on clinopyroxene. Here, we integrate in-situ major and trace element analyses and Sr isotopic ratios of plagioclase phenocrysts with textural observations to reconstruct the magma evolution of Pako guyot in detail. Plagioclase phenocryst cores exhibit resorption textures with significantly higher An content (=100Ca/(K + Na + Ca), molecular ratio; 48–80) compared to their rims (223–70), while groundmass plagioclase (45–55) has similar An values to the rims, indicating that the cores are antecrysts in textural and chemical disequilibrium with the host melt. The Pako plagioclase phenocrysts show variable Sr isotopic ratios (0.7045–0.7055) and trace element concentrations at a limited An range indicating that these plagioclase crystals crystallized from heterogeneous melts. Combining plagioclase and clinopyroxene data, we propose a multi-stage magmatic model where early-formed clinopyroxene and plagioclase crystals accumulated to form a crystal mush and subsequent magma recharge and mixing processes resulted in diverse zoning textures and chemical compositions of these crystals. Zoning texture and chemical composition of plagioclase and clinopyroxene phenocrysts reveal that the melts built the Pako guyot are compositionally heterogeneous.