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Lisa Gahagan and Paul Mann, Institute for Geophysics, University of Texas at Austin

Subduction of the Cocos and Carnegie ridges at the Middle America and Colombian trenches, respectively, have been shown by a variety of marine and land-based studies to have profound and disruptive effects on subaerial and submarine geomorphology, the spacing and composition of arc volcanism, cross-arc traverse faulting, forearc deformation and erosion, back-arc thrust faulting, and anomalously large forearc and backarc thrust-related earthquakes. To better understand past effects of these highly localized, collisional-driven processes, we use quantitative plate reconstructions to reconstruct the history of three originally, contiguous large igneous provinces (Cocos, Malpelo, Carnegie ridges) formed near the Galapagos hotspot in early Miocene time (~21 Ma). Plate reconstructions are based on a compilation of marine magnetic data from the Cocos, Nazca, Pacific, and Caribbean plates and make use of plate closure between those plates via circuits through Cocos-Nazca-Antarctica-Pacific and Antarctica-Africa-North America-Caribbean. Main events suggested by this reconstruction include: 1) formation of the Cocos-Malpelo-Carnegie ridges as a single large igneous province (LIP) in the vicinity of the Galapagos hotspot starting at ~21 Ma; 2) predicted formation of a now-subducted northeastward extension of the Cocos Ridge between 20-14 Ma; 3) rifting and divergence of the three LIPs occurred between 21 and 12 Ma following formation of the Nazca-Cocos plate boundary; 4) 750 km of right-lateral offset of the Cocos Ridge into an eastern (Malpelo) and western (Cocos) branch; 5) initial contact of the inferred extension of the Cocos Ridge with the Middle America trench at ~2 Ma; and 6) subduction of ~225 km of the inferred extension of the Cocos Ridge. We compare our predicted Cocos ridge subduction history with land-based geologic studies of deformation and uplift.