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Chapter 2: The Ribbon Continent of South America in Ecuador, Colombia, and Venezuela
Isotopic ages in volcanic arc igneous and subduction complex rocks in Venezuela and on the offshore island of Aruba are consistent with the finding that the ages of arc igneous activity and high pressure–low temperature metamorphism in both of those areas are restricted to times between ca 150 Ma and ca 70 Ma. That age range, and the restriction of fossil ages in the subduction complexes to between mid-Jurassic (ca 170 Ma) and late Cretaceous (ca 70 Ma) times, reveals a match to the ages of volcanic arc rocks that were involved in collision with the Andean Margin of Ecuador more than 2000 km (1242.7 mi) away. The similarity of ages can be explained if the rocks in both areas are those of the Great Arc of the Caribbean, which has been considered to have collided with the west coast of South America during the late Cretaceous. Synthesizing results from Ecuador and Colombia shows that in those areas the Great Arc was involved in collisions, first with the Caribbean–Colombian Oceanic Plateau (CCOP) and then with the Andean Margin of South America. By 70 Ma a ca 200-km(124.2-mi)-wide Ribbon Continent consisting of fragments of both the Great Arc of the Caribbean and the CCOP was traveling to the north in a transpressive plate boundary zone (PBZ) along the Colombian coast.
By 65 Ma, as the CCOP began to enter the Atlantic Ocean and a newly formed Caribbean plate (CARIB) separated from the Farallon plate, parts of the Ribbon Continent began to be carried in a southern CARIB transform PBZ eastward along the north coast of South America. We characterize three W–E-trending belts in that part of the Ribbon Continent: (1) a Northern Belt consisting largely of Great Arc of the Caribbean intrusions and subduction complex rocks; (2) a Central Belt, very well known in Venezuela, consisting of Great Arc of the Caribbean subduction complex rocks; and (3) a fold-and-thrust belt in the Serrania del Interior and Lara nappes of Venezuela. A receiver function (seismic) study has shown where rocks of the Great Arc of the Caribbean abut the South American continent along an E–W-trending line in Venezuela. We find that rocks of both the subduction complex of the Great Arc and rocks of the Serrania del Interior have been thrust across that boundary in secondary thrusts as the Ribbon Continent has propagated to the east in the South Caribbean transform PBZ.
The structure of the north coast of South America is being radically altered by the northward movement of the Maracaibo Block as it escapes from deformation related to the collision of the Panama Arc with Colombia. Restoration of movements within that block during the past 15 My has been essential to reconstruct the structure and history of the Ribbon Continent on the north coast of South America.
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