Along-strike variations in the thermal and tectonic response of the continental Ecuadorian Andes to the collision with heterogeneous oceanic crust

Oblique to strike geological segmentation in the Andean chain has been prev iously recognised at Various scales and is commonly attributed to changes i n the convergence vectors of the oceanic and continental plates, as well as the upper-plate expressions of differing along-strike subducted slab age, strength and composition. We present new white mica and biotite Ar-40/Ar-39 and zircon and apatite fission-track data from several traverses across th e Cordillera Real of Ecuador in the northern Andes that reveal distinct alo ng-strike differences in the timing of accelerated crustal cooling during t he Cenozoic, The data record elevated cooling rates from temperatures of si milar to 380 degreesC during similar to 65-55 and similar to 43-30 Ma from all sampled regions of the Cordillera Real and at similar to 15 Ma and sinc e similar to9 Ma in the northern Cordillera Real. Each cooling period was p robably driven by exhumation in response to the accretion and subduction of heterogeneous oceanic crust. Elevated cooling rates of up to similar to 30 -20 degreesC/Myr were initiated during the Palaeocene and Eocene-early Olig ocene along the entire contemporaneous margin of Ecuador and were driven by the accretion of the oceanic Pallatanga Terrane and Pinon-Macuchi Block, r espectively, onto northwestern South America. Both of these geological prov inces originated at the southern parts of the leading and trailing boundari es of the Caribbean Plateau and accreted onto the margin during the approxi mately northeastward migration of the Plateau into its current position. Wi thin Ecuador the development of higher topography and elevated cooling rate s of up to 50 degreesC/Myr at similar to 15 Ma and since Ng Ma are restrict ed to the region north of 1 degrees 30'S and is situated above the postulat ed subducted flat-slab section of the aseismic Carnegie Ridge. Plate conver gence rate calculations suggest the Carnegie Ridge collided with the Ecuado r Trench at similar to 15 Ma, which caused the pre-existing coastal provinc es to displace to the northeast, subsequently driving extension and marine ingressions in southern Ecuador and compression and uplift in northern Ecua dor. (C) 2001 Elsevier Science B.V, All rights reserved.