PROVENANCE AND GEOCHEMICAL ANALYSIS OF THE NORTHERN RANGE, TRINIDAD

Geochemical compositions and petrographic analyses of 13 metasedimentary bedrock samples from the Northern Range, Trinidad were used to interpret tectonic provenance, paleoweathering, and tectonic depositional setting. Petrographic analysis reveals samples are dominated by monocrystalline quartz typically greater than ~95%, with only two samples containing more than ~30% feldspars. Sedimentary provenance is based on modal plots and major element discriminant functions and provenance suggests Northern Range sediments were derived from felsic igneous rocks, predominantly from a cratonic interior with minor contributions from a transitional continental setting. Geochemical analyses were also used to infer paleoweathering conditions of the source terrain and include: (1) the Chemical Index of Alteration (CIA); (2) the Index of Compositional Variability (ICV); and (3) the Plagioclase Index of Alteration (PIA). These index values for most samples indicate highly weathered and compositionally mature source sediments (e.g., CIA is 75-85), while the two samples with feldspars present have significantly lower degrees of chemical weathering (e.g., CIA is < 70). Several elemental discrimination analyses including binary plots of TiO₂ against (Fe₂O₃ + MgO) and ternary plots of are used to decipher the depositional tectonic setting and are all generally associated with deposition in a passive margin setting. Overall, these results indicate that the sedimentary protolith of the Northern Range metasediments were most likely derived from highly weathered felsic igneous rocks sourced from a cratonic interior and subsequently deposited along a passive margin. Potential source areas within the interior of northern South America are identified and possible sediment transport and depositional river systems are explored.