Figure F2. Leg 170 and 205 Costa Rica drilling area and isochrons derived from seafloor magnetic anomalies (Barckhausen et al., 2001). Numbers indicate crustal age in millions of years. Fracture zone trace marks location where spreading of the Cocos-Nazca spreading center (CNS) initiates; triple junction trace separates crust formed at the CNS and the East Pacific Rise. The ridge jump records the change from CNS-1 to CNS-2 spreading (~19.5 Ma). Convergence direction and rate (DeMets et al., 1990) and arc volcanoes (triangles) are also shown. Note the segmentation of the volcanic arc and the offset in Wadati-Benioff Zone isodepths at the Quesada Sharp Contortion (QSC). Figure modified after Barckhausen et al., 2001. Sill intrusion zone redrawn after Silver et al., 2004.

Figure F2. Leg 170 and 205 Costa Rica drilling area and isochrons derived from seafloor magnetic anomalies (Barckhausen et al., 2001). Numbers indicate crustal age in millions of years. Fracture zone trace marks location where spreading of the Cocos-Nazca spreading center (CNS) initiates; triple junction trace separates crust formed at the CNS and the East Pacific Rise. The ridge jump records the change from CNS-1 to CNS-2 spreading (~19.5 Ma). Convergence direction and rate (DeMets et al., 1990) and arc volcanoes (triangles) are also shown. Note the segmentation of the volcanic arc and the offset in Wadati-Benioff Zone isodepths at the Quesada Sharp Contortion (QSC). Figure modified after Barckhausen et al., 2001. Sill intrusion zone redrawn after Silver et al., 2004.