Geological provinces (A) and sample sites (B) are colored by their province location: outer forearc (blue), forearc (orange), and arc (red). A The green arrow indicates the location of trench, black arrows show the direction of plate movements, blue arrows show fluids and degassing throughout subduction. B Green dotted line indicates the trench while gray dotted lines mark the depth of the 122 °C isotherm in 5 km increments, based on data for this region of Costa Rica from Harris and Wang 2010. Locations of volcanoes are shown with volcano icons. Dotted white line demarcates the plates emerging from the East Pacific Rise (EPR) and the Cocos Nazca Spreading center (CNS).