Thermochronology constraints on Miocene exhumation in the Central Range Mountains, Trinidad

Abstract

The Central Range fault zone is a continental transform that accommodates most of the present-day slip between the Caribbean and South American plates in Trinidad. Global positioning system data and paleoseismic work suggest that this zone is active today and has been active for at least the past several thousand years. The modern fault zone overprints a middle Miocene fold-and-thrust belt; therefore, the strain recorded in the Central Range fault zone is the sum of both middle Miocene and more recent events. Thermochronology data from Eocene and Oligocene sandstones in the Central Range were collected to evaluate the timing of exhumation driven by crustal shortening and thickening. (U-Th)/He zircon analysis of subhedral zircons collected from eight samples indicated that the burial temperatures of these sedimentary rocks did not exceed ∼180 °C, suggesting that these grains record detrital (U-Th)/He dates. Apatite fission-track (AFT) analysis of 10 samples yielded mixed results, with cooling ages ranging from 30 to 15 Ma; however, most sites failed the χ2 test, suggesting that multiple age cohorts are present. Pooled AFT ages suggest that rocks presently at the surface were exhumed through their AFT closure temperature ca. 11−18 Ma. Cooling and exhumation thus most likely resulted from middle Miocene shortening across the fold-and-thrust belt in response to early oblique convergence between the Caribbean and South America plates. Post-Miocene deformation associated with more recent transform tectonics has therefore resulted in more limited (<∼4 km), if any, exhumation.