The early interaction between the Caribbean plateau and the NW South American Plate

The determination of accurate and precise ages for the timing of collision between oceanic plateaus and continental crust requires an understanding of how the indenting and buttressing plates respond to the collision. We present geochronological, thermochronological, geochemical and isotopic analyses of magmatic rocks from the Ecuadorian Andes, which relate to the collision of the Late Cretaceous Caribbean Plateau and Great Arc sequence with NW South America. The cessation of subduction magmatism during 65-64 Ma beneath the eastern edge of Caribbean Plateau was synchronous with accelerated surface uplift and exhumation within the buttressing continental margin during 75-65 Ma. We interpret this as the collision of the leading edge of the Caribbean Plateau and arc sequence with the South American Plate at 75-65 Ma. A U/Pb (zircon) SHRIMP age of 87.10 +/- 1.66 (2 sigma) Ma, yielded by an accreted fragment of the plateau, precludes previous estimates of collision at 85-80 Ma if the plateau erupted above the Galapagos hotspot.