YOU CAN ONLY SQUEEZE IT SO HARD - CRUSTAL ESCAPE IN CENTRAL AMERICA ASSOCIATED WITH COCOS RIDGE SUBDUCTION

One of the paradigms for generation of Andean-style mountain belts involves subduction of aseismic ridges such as the Nazca or Carnegie Ridges. When these ridges are superimposed on relatively young lithosphere (e.g., Nazca plate) the resulting buoyant oceanic crust promotes high coupling along the subduction interface, possibly leading to flat slab subduction, high compressive stresses across a broad region, and crustal thickening and uplift via fold and thrust belt development.

Kinematic observations in Central America allow this process to be studied in its early stages. In southern Costa Rica and northern Panama, the Cocos Ridge began subducting less than 3.5 million years ago, causing cessation of volcanism, fold and thrust belt development, and shortening and uplift at rates comparable to the Andean example. Much of the region to the north (from central Costa Rica to Guatemala) does not experience shortening or uplift, but rather trench-parallel transport of a fore-arc sliver block, previously assumed to reflect oblique subduction. Additionally, the region to the south (Panama) is being driven to the east-northeast. High precision GPS measurements suggest that crustal escape associated with Cocos Ridge collision is a key factor in upper plate deformation, including fore-arc motion, limiting the amount of shortening to a relatively narrow zone (~175 km measured in the trench-parallel direction) close to the center of the Cocos Ridge. Perhaps subduction of aseismic ridges is a necessary but not sufficient condition for generation of Andean-style mountain belts, and additional tectonic/geometric factors are required. Alternately, southern Central America may be in the early stages of Andean orogeny.