Figure F1. Leg 205 Costa Rica drilling area (red box) and isochrons derived from seafloor magnetic anomalies (Barckhausen et al., 2001). Numbers indicate crustal age in millions of years. Tectonic boundaries, convergence direction and rate (arrows; DeMets et al., 1990), and arc volcanoes (triangles) are shown. Drill sites of Leg 205 (red square) are located on crust generated at the East Pacific Rise (EPR), which converges with a rate of 88 mm/yr (DeMets et al., 1990) toward the Carribean plate. Inset is of seismic Profile BGR 99-44 (C. Reichert and C. Ranero, pers. comm., 2001) across the Middle American Trench. Sites 1039–1043 were drilled during Leg 170 (Kimura, Silver, Blum et al., 1997); Sites 1253–1255 (red) were added during Leg 205 (Morris, Villinger, Klaus, et al., 2003). At 6.34 s two-way traveltime, the basement reflection corresponding to the sill can be identified beneath the location of Site 1039 and 1253. CNS = Cocos-Nazca spreading center, FS = Fisher Seamount.

Figure F1. Leg 205 Costa Rica drilling area (red box) and isochrons derived from seafloor magnetic anomalies (Barckhausen et al., 2001). Numbers indicate crustal age in millions of years. Tectonic boundaries, convergence direction and rate (arrows; DeMets et al., 1990), and arc volcanoes (triangles) are shown. Drill sites of Leg 205 (red square) are located on crust generated at the East Pacific Rise (EPR), which converges with a rate of 88 mm/yr (DeMets et al., 1990) toward the Carribean plate. Inset is of seismic Profile BGR 99-44 (C. Reichert and C. Ranero, pers. comm., 2001) across the Middle American Trench. Sites 1039–1043 were drilled during Leg 170 (Kimura, Silver, Blum et al., 1997); Sites 1253–1255 (red) were added during Leg 205 (Morris, Villinger, Klaus, et al., 2003). At 6.34 s two-way traveltime, the basement reflection corresponding to the sill can be identified beneath the location of Site 1039 and 1253. CNS = Cocos-Nazca spreading center, FS = Fisher Seamount.