COCOS RIDGE COLLISION, DEFORMATION OF THE WESTERN CARIBBEAN AND FINAL CLOSURE OF THE ISTHMUS OF PANAMA

We test the hypothesis that the Cocos Ridge is the main driver for upper plate deformation, including horizontal motion of the Panamanian Isthmus and uplift directly inboard of the ridge, in the western Caribbean. We first compare geodynamic models of ridge collision to a new 1993-2015 GPS-derived horizontal velocity and strain rate field for the western Caribbean and northwestern South America and then to longer-term geologic deformation of the region. The collision of the Panamanian Isthmus with northwestern South America is thought to have initiated as early as Oligocene - Miocene time (25-23 Ma) based on geologic and geophysical data and paleogeographic reconstructions. This collision was driven by east-directed subduction of the Caribbean beneath northwestern South America and resulted in deformation of the Panama Region and South American margin. Subduction and collision of the aseismic Cocos Ridge is thought to have initiated <3.5 Ma and has been linked to uplift and shortening across the isthmus and motion of the Central American forearc.

Our model domain includes the Central American forearc block and Panama Region, the Caribbean and Nazca plates and the North Andes and Choco blocks. We model Cocos Ridge collision using velocity boundary conditions and test the boundary condition of northwestward motion of the North Andes block. Our modeled horizontal velocities and strain rates are comparable to our observations (GPS), and indicate that Cocos Ridge collision drives northwest-directed motion of the CAFA and the northeast-directed motion of the Panama Region. The Panama Region is driven into the Caribbean across the NPDB, hypothesized to have formed during initial collision of the isthmus with South America, and into northwestern South America, which is also converging with the Panama Region, pushing it toward the west-northwest. Therefore, when we extrapolate our best-matching model, we find that recent (<3.5 Ma) collision of Cocos Ridge with the western Caribbean has driven collision of Panama with northwestern South America, and complex deformation of the upper plate (i.e., uplift and shortening of the forearc and volcanic arc, and motion of the forearc), and potentially the final closure of the Isthmus of Panama.