Accreted oceanic terranes in Ecuador: Southern edge of the Caribbean plate ?
Résumé
The western part of Ecuador is made of several oceanic terranes, which comprise two oceanic plateaus, of Early (≈ 120 Ma), and Late Cretaceous age (≈ 90 Ma), respectively. The older oceanic plateau was accreted to the andean margin in the Late Campanian (≈ 75 Ma). Fragments of the Turonian-Coniacian plateau were accreted to the ecuadorian margin in the Late Maastrichtian (≈ 68 Ma, Guaranda terrane) and Late Paleocene (≈ 58 Ma, Piñón-Naranjal terrane). The Guaranda terrane received either fine-grained oceanic sediments of Coniacian-Maastrichtian age, or island arc / back-arc volcanic suites of Middle Campanian-Middle Maastrichtian age. The Piñón-Naranjal terrane recorded a comparable history, completed in the Maastrichtian-Paleocene, either by pelagic cherts, or by island arc products (Macuchi arc). The Late Cretaceous plateau of Ecuador is interpreted as part of the Caribbean oceanic plateau (COP), because their evolutions are comparable. If so, the COP was not formed by the Galápagos hotspot, but on the Farallón oceanic plate, south of Ecuador and close to the South American margin. The COP belonged to the Farallón plate, until a subduction zone separated both plates in the Middle Campanian, giving way to a well developed Mid Campanian-Mid Maastrichtian island arc. Accretion in the Late Maastrichtian triggered a change in the subduction system, and the development of a new arc system of Late Maastrichtian-Late Paleocene age, which crosscut the South America-COP plate boundary. The last accretion occurred in the Late Paleocene.
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