Origin and Cretaceous tectonic history of the coastal Ecuadorian forearc between 1°N and 3°S: Paleomagnetic, radiometric and fossil evidence

Abstract

The presence of at least one Block (Pallatanga Block) derived from the Caribbean–Colombian Oceanic Plateau has been proposed in the Western Cordillera of Ecuador. New 40Ar/ 39Ar dating of the basement of the coastal blocks (90–87 Ma) and fossil ages in the overlying Calentura Fm. (89–84 Ma) argue for late Turonian–Coniacian extrusion of the basement of the Piñon block. Paleomagnetic inclinations indicate that the mafic basement of the Piñon and San Lorenzo blocks extruded at equatorial, low southern latitudes. No subsequent significant latitudinal drift can be observed during the Cretaceous. Rapid changes in paleomagnetic declination between 73 and 70 Ma in both the Piñon and the San Lorenzo blocks indicate that the large igneous province, which originally hosted the coastal blocks experienced a major tectonic event during Late Campanian times. Similar Late Turonian–Coniacian basement ages and Late Campanian tectonic events are reported in the Pallatanga Block of the Western Cordillera. We propose that the Piñon, San Lorenzo and Pallatanga blocks all derive from a common large igneous province, the Caribbean–Colombian Oceanic Plateau, and were incorporated into the South American margin by collision during the Late Campanian (73–70 Ma).