THERMOCHRONOLOGIC CONSTRAINTS ON TRANSPRESSIONAL EXHUMATION, CENTRAL RANGE FAULT ZONE, TRINIDAD

The Central Range fault zone in Trinidad marks the active boundary between the Caribbean and South American plates just off of the coast of Venezuela. Previous GPS studies demonstrate that the fault zone is currently obliquely convergent. Modern transpression overprints and reactivates a Miocene fold and thrust belt. Mountains in the Central Range are low relief and gravity data indicate the range is underlain by a small crustal root. Thermochronology samples, both apatite fission-track and zircon (U-Th)/He, from Eocene and Oligocene sandstone in the Central Range place constraints on the timing and amount of exhumation in the Central Range Mountains. Apatite fission-track data yield mixed results with cooling ages ranging from 30 to 15 Ma, however most sites fail the chi-squared test suggesting multiple age populations. Pooled apatite fission-track ages suggest that rocks currently at the surface were exhumed through the partial annealing zone in response to Miocene contraction. Apatite grains >50 microns in diameter were not present, therefore apatite (U-Th)/He data could not be collected. Zircon (U-Th)/He ages preserve a provenance signal in all samples, indicating that Oligocene to recent burial did not exceed the zircon (U-Th)/He closure temperature (approx. 180˚C). These data place an upper bound of about seven kilometers for the total exhumation magnitude of the Central Range. Contraction in the Miocene caused at least half of the unroofing and moved the samples into the apatite partial annealing zone (100˚C to 60˚C). It is unclear how much of the remaining exhumation occurred during the Miocene vs. the more recently obliquely convergent plate motion. The presence of a shallow crustal root under a small, low relief mountain range, however, strongly suggests that some of this exhumation was accomplished by the presently active system.