Regional provenance study of Eocene clastic sedimentary rocks within the South America–Caribbean plate boundary zone using detrital zircon geochronology

Abstract

Previous on- and offshore studies have postulated that the Caribbean plate has translated hundreds of kilometers eastward during the Cenozoic along strike-slip and oblique thrust faults bounding the northern margin of the continental South America plate. Two previously proposed tectonic-sedimentary models to explain the complex linkages between plate motions and sedimentation within the broad plate boundary zone include: 1) eastward bulldozing by the Caribbean plate of a single, large point source, thick Eocene proto-Maracaibo deltaic system of northwestern South America, over 1000 km to the east and incorporation of these continentally derived sediments into the ∼ 12-km-thick Barbados accretionary prism along the leading edge of the Caribbean plate; and 2) eastward bulldozing by less than 300 km of smaller point and line sources of Eocene and younger clastic sediments derived from erosion of the Guyana shield located in north-central and northeastern South America. We test both models by sampling eight Eocene localities that span a 1200-km-length of the plate boundary zone from the proto-Maracaibo delta in western Venezuela to Barbados Island in the subaerial part of the large accretionary prism bounding the eastern margin of the Caribbean plate. Ages of 972 single grains from samples at these eight localities support the multiple-source model, in which the Barbados prism was partly constructed from the bulldozing and incorporation of smaller point and line sources derived from older-than 1500 Ma crustal provinces of the Precambrian Guyana shield in central and northeastern South America. Eocene clastic sediments of the proto-Maracaibo delta derived from Paleozoic and Precambrian crustal provinces in northwestern South America are distinct in their ranges of detrital zircon ages from the ranges of the Guyana shield sources to the east.