Seismic Constraints on Igneous Intrusions and Fluid/Gas Distribution in a Continental Back‐Arc System: Evidence From the Yaeyama Rift in the Southern Okinawa Trough

The geometry and distribution of igneous intrusions, which define melt source locations and record syn‐emplacement stress conditions, are essential for understanding tectonic and magmatic processes associated with crustal extension. However, in back‐arc settings along continental margins, structural constraints on these features remain poorly documented. In the southern Okinawa Trough—an active back‐arc basin transitioning from rifting to seafloor spreading—previous studies have identified narrow subsurface intrusions resulting from the magma ascent driven by lithospheric extension beneath the linear topographic depression known as the Yaeyama Rift. Here, we present new seismic reflection data that constrain the pseudo‐three‐dimensional geometry of intrusions beneath the Yaeyama Rift. Seven across‐rift and one along‐rift seismic profiles reveal complex rift structures, including a rapid transition from exposed magmatic bodies forming the Yaeyama Knoll to buried intrusions capped by graben structures, suggesting caldera collapse. Although the Yaeyama Rift generally exhibits low heat flow values (<70 mW/m 2 ), the deep intrusive body is linked to a high‐temperature hydrothermal venting site on the Yaeyama Knoll. Additional narrower intrusion structures are also identified beneath rift margins and off‐axis regions where a dense network of normal faults has developed and may influence local thermal structure through structural heat focusing. Nearby, we identify seismic reflectors with polarity reversal and stratigraphic layers with reduced reflection amplitudes that indicate fluid and gas accumulations at depth. These findings suggest a close interplay between heat supplied by deep plutonic intrusions and the cooling effects of thick sedimentary layers, plus seawater inflow through syn‐rift normal faults.