The southernmost M ariana forearc stretched to accommodate opening of the M ariana T rough backarc basin in late N eogene time, erupting basalts at 3.7–2.7 Ma that are now exposed in the Southeast M ariana F orearc R ift ( SEMFR ). T oday, SEMFR is a broad zone of extension that formed on hydrated, forearc lithosphere and overlies the shallow subducting slab (slab depth ≤ 30–50 km). It comprises NW–SE trending subparallel deep...

West Rota Volcano (WRV) is a recently discovered extinct submarine volcano in the southern Mariana Arc. It is large (25 km diameter base), shallow (up to 300 m below sealevel), and contains a large caldera (6 × 10 km, with up to 1 km relief). The WRV lies near the northern termination of a major NNE‐trending normal fault. This and a second, parallel fault just west of the volcano separate uplifted, thick frontal arc crust to t...