CONSTRAINTS ON UPLIFT FROM GEOMORPHIC ANALYSIS OF A DIGITAL ELEVATION MODEL OF THE CENTRAL RANGE MOUNTAINS, TRINIDAD

Trinidad is located on the boundary between the South American continent and the Caribbean Plate, which translates eastward approximately 20 mm/yr, relative to a fixed South American. This movement is primarily expressed in the Central Range Fault zone (CRFZ), which accommodates 12 mm/yr of strike-slip motion and 4 mm/yr of convergence. The transpressional nature of the CRFZ is reflected in the rise of the Central Range Mountains, which likely began forming at the same time the CRFZ became active. We used ArcGIS to analyze an ASTER-based digital elevation model (DEM) to characterize 23 drainage basins within the CRFZ. Elevation and area data for each basin were imported into MATLAB to generate hypsometric curves, used as a proxy for the maturity of the basins. Twenty-one basins displayed mature curve profiles, while the remaining two were characterized by less mature, more linear hypsometry. The relatively small size of these two drainage basins, along with the weakly resistant siltstone and shale bedrock characteristic of the CRFZ, may account for the variation in basin maturity. Erosional processes in larger stream basins may be occurring at rates that rapidly eliminate any significant changes to hypsometry created by tectonic uplift. Long profiles from each basin suggest that knickpoints are preserved throughout the CRFZ. Analysis of the frequency distribution of elevations in the long profiles suggest a local base level of approximately 20 m elevation and an uplifted surface at approximately 70 m in elevation. Together these values imply the Central Range has experienced at least 50 meters of uplift. The Central Range Mountains have an average divide height of 150 m which equates to a mean erosion rate of 0.01 mm/yr following the relief vs. erosion rate data compiled by Montgomery and Brandon (2002). Removal of 50 m at 0.01 mm/yr implies that uplift in the CRFZ began 5 Ma. The true rate of erosion, however, is likely higher than that suggested by the global data set presented by Montgomery and Brandon (2002) because of the tropical climate in Trinidad and weakly-resistant bedrock. This age estimate could be improved greatly by local constraints on erosion rate (e.g. cosmogenic studies). Regardless, both the hypsometric and long profile analyses indicate that a tectonic signal is preserved in the topography of the CRFZ.