Across‐Arc Diversity in Rhyolites From an Intra‐oceanic Arc: Evidence From IODP Site U1437, Izu‐Bonin Rear Arc, and Surrounding Area

Abstract

Abstract Felsic magmas from the Izu‐Bonin rear arc have compositions that resemble average continental crust in some respects. In order to understand their origin, we studied 1.1–4.4 Ma tephras in a rear‐arc drill core from International Ocean Discovery Program Expedition 350, Site U1437. They provide a well‐dated record of changing magmatic compositions during the early stages of the most recent episode of Izu‐Bonin arc rifting. Based on our comprehensive recontextualization of published analyses of 73% SiO2. However, trace element and Hf isotope ratios preclude rear‐arc rhyolite derivation by partial melting of the Oligocene‐Eocene arc basement. Thus, we favor a model where fractional crystallization is more important than crustal melting in producing intra‐oceanic arc rhyolites in this region.

Keywords

• intra‐oceanic arc
• arc magmatism
• Izu‐Bonin Arc
• closed‐system fractional crystallization
• arc crust