Basalt derived from highly refractory mantle sources during early Izu-Bonin-Mariana arc development
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The magmatic character of early subduction zone and arc development is unlike mature systems. Low-Ti-K tholeiitic basalts and boninites dominate the early Izu-Bonin-Mariana (IBM) system. Basalts recovered from the Amami Sankaku Basin (ASB), underlying and located west of the IBM’s oldest remnant arc, erupted at ~49 Ma. This was 3 million years after subduction inception (51-52 Ma) represented by forearc basalt (FAB), at the tipping point between FAB-boninite and typical arc magmatism. We show ASB basalts are low-Ti-K, aluminous spinel-bearing tholeiites, distinct compared to mid-ocean ridge (MOR), backarc basin, island arc or ocean island basalts. Their upper mantle source was hot, reduced, refractory peridotite, indicating prior melt extraction. ASB basalts transferred rapidly from pressures (~0.7-2 GPa) at the plagioclase-spinel peridotite facies boundary to the surface. Vestiges of a polybaric-polythermal mineralogy are preserved in this basalt, and were not obliterated during persistent recharge-mix-tap-fractionate regimes typical of MOR or mature arcs.
Li, He; Arculus, Richard J.; Ishizuka, Osamu; Hickey-Vargas, Rosemary; Yogodzinski, Gene M.; McCarthy, Anders; Kusano, Yuki; Brandl, Philipp A.; Savov, Ivan P.; Tepley, Frank J.; and Sun, Weidong, "Basalt derived from highly refractory mantle sources during early Izu-Bonin-Mariana arc development" (2021). All Faculty. 289.