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Abstract

We performed zircon fission-track dating on twenty low-grade metamorphic rocks from the Northern Range and eight unmetamorphosed sandstones from the Central Range of Trinidad. Reset and partially reset zircon populations from the Northern Range gave a consistent fission-track age of 11.7 ± 1.1 Ma. This dates the cooling of the Northern Range through 240 ± 25°C. Assuming a geothermal gradient of 25°C km 1 which is unproved, and a constant rate of uplift, the Northern Range uplifted at an average rate of 0.7 to 1.0 mm yr 1 from the Late Miocene to Recent. If the uplift was not at a constant rate, then the true uplift rates may have been greater than 1.0 mm yr-1. In areas of lower grade metamorphism, Northern Range zircon fission-track ages were not reset, and thus gave information on the provenance of the Cretaceous sediments. Permian and Late Jurassic fission-track ages determined for the Maastrichtian Galera Formation sandstones are interpreted to have been derived, respectively, from granitoids and rift-related volcanics along the northern South American margin. Albian and Early Silurian/Late Ordovician zircon fission-track ages from the Lower Cretaceous Toco Formation have no provenance local to Trinidad but may have been derived further west, possibly from the Caribbean island arc and northern Andes respectively. This difference between the two formations is entirely consistent with structural and stratigraphic work which show the Toco Formation to be part of the Sans Souci Group, an allochthonous terrane transported from the west with the Caribbean plate. The Galera Formation is part of the Northern Range Group, which makes up the majority of the Northern Range, and is inteipreted to have been deposited on the northern South American margin, probably within 400 km of its present location.

Zircon fission-track ages from unmetamorphosed sandstones of central Trinidad’s Pointe-a-Pierre Formation constrain deposition of the formation to later than 34 Ma (Lower-Middle Oligocene or later). This is much younger than the faunally estimated Lower Eocene (55 Ma) depositional age, probably because the fauna, which are “arenaceous,” have been reworked. Similar zircon fission-track ages are found in central Trinidad’s Nariva Formation, which is faunally dated as Middle Oligocene to Middle Miocene age.

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