Geological evolutionary model of the Costa Rica subduction margin

The Middle American Trench (MAT) is one of the most complex subduction margins all over the earth surface. Its geodynamical complexity is due to the interaction between five major lithospheric plates: North America, Caribbean, Cocos, Nazca and South America; between them is the Panama microplate. We focused on the Costa Rica subduction margin, which is a portion of the MAT and it is characterized by some peculiarities with respect to the other portions of the MAT. Along the Costa Rica offshore the subduction of the Cocos Plate is currently developing towards NE, beneath both the Caribbean Plate and the Panama Microplate, with a rate that increases from NW (87 mm/yr), in correspondence of the Nicoya Peninsula, to SE (92-95 mm/yr), in correspondence of the Osa Peninsula.    The Cocos Plate formed, together with the Nazca Plate, about 28 Ma from the Farallon Plate fragmentation in turn due to the formation of the East Pacific Rise (EPR). The subduction process is extremely seismogenetic and caused some earthquakes up to 7.8 Mw (1950): one of the most recent hits Nicoya on September 5th, 2012 (Mw 7.6). The migration of the Cocos Plate towards the Galapagos plume generated, about 14 Ma, the Cocos Ridge, a strip of oceanic ridge that is currently subducting beneath the southeastern margin of Costa Rica, in correspondence of the Osa Peninsula. The beginning of subduction, dated between 8 and 1 Ma, generated an isostatic rebound that gave rise to a general uplift generating the Cordillera de Talamanca, which emerged between 4.5 and 3 Ma and representing the extinct portion of the volcanic arc.     The main aim of this study is to provide a reliable model about the evolution of the Costa Rica subduction margin, paying attention on the Cocos Ridge subduction and to understand how this affects the evolution of the margin. Through the seismostratigraphic interpretation of several multichannel seismic reflection profiles, together with morphobathymetric data, well data from ODP Leg 170, focal mechanisms and oceanic crust age variation chart along the MAT, as well as the Costa Rica geological map, produced by USGS, we recognized some evidence and mechanisms responsible for the uplift that affected the area (e.g. underthrusting process and strike-slip faults) and how this could be related to the subduction of the Cocos Ridge and of several seamounts recognized along the Costa Rica subduction margin. The Cocos Ridge subduction is also responsible for the magmatism recognized along the Nicoya Peninsula offshore, as well as of the variation of the slab geometry recognized through the realization of a 3D model of the Wadati-Benioff Plane.