Paper No. 4
Presentation Time: 8:00 AM-4:45 PM
Detrital Zircon Geochronology of Paleocene/Eocene Turbidites from Venezuela and Offshore Islands: Implications for Late Cretaceous Subduction Initiation along the Leeward Antilles and Aves Ridge
Quartz rich southerly derived passive margin sedimentation along the Venezuelan continental margin was interrupted in the Paleocene/Eocene and Miocene when turbidites with a mainly northerly source were deposited (the Matatere, Guarico, Los Cajones, Garrapata, Caratas and Los Arroyos formations). The turbidites are compositionally immature and rich in volcanic, chert, and metamorphic framework grains as well as abundant detrital plagioclase and quartz, whereas passive margin sedimentation was dominated by compositionally mature sandstones consisting principally of mono crystalline quartz. Paleocene/Eocene turbidites are also present on Curacao, Bonaire, Margarita island and Barbados. All of these units (Venezuelan margin and off shore islands) have a mixed continental margin and volcanic arc provenance and were probably derived from reworking of passive margin units as well as from the Leeward Antilles/Aves ridge. Preliminary apatite fission track and U-Th-He dating suggest rapid exhumation of the Leeward Antilles in Paleocene/Eocene time and thus are a potential source for the arc detritus. Our preliminary U-Pb detrital zircon data from Paleocene/Eocene turbidites on Curacao support a mixed arc/continental margin provenance. Detrital zircon ages range from 66 Ma to 2.7Ga. Cretaceous age grains have a prominent peak at 75 Ma with only a few grains that date back to as old as 89 Ma. We will present additional data from the units discussed above. Our preliminary interpretation is that arc magmatism initiated along the Aves Ridge/Leeward Antilles in the Late Cretaceous and was constructed on a basement of the slightly older Caribbean Large Igneous Complex (CLIP). The Leeward Antilles/Aves Ridge do not have a significant Greater Antilles arc basement. We suggest that the Greater Antilles arc terminated southward at a transform boundary that separated proto Caribbean oceanic crust from the Greater Antilles arc and the CLIP. Subduction initiation along the transform generated the Leeward Antilles/Aves Ridge island arc.