CONSTRAINING THE TIMING OF DEFORMATION OF THE SOUTHERN BASIN AND RANGE, TRINIDAD USING ZIRCON AND APATITE (U-TH)/HE THERMOCHRONOLOGY

The Southern Basin and Southern Range of the Caribbean island of Trinidad are comprised of folded post-middle Miocene sedimentary strata. This basin and the low elevation (~300m) mountains are located 20-30 km south of the modern Caribbean-South American plate boundary. The strike-slip Central Range Fault accommodates most of the total relative modern plate motion, yet it is unclear how much and where plate strain has been partitioned in southern Trinidad in the geologic past. To investigate the exhumation history of this region, apatite and zircon (U-Th)/He (AHe and ZHe, respectively) thermochronology were utilized. Three sandstone bedrock samples from the Southern Range yield very young (Quaternary) mean AHe aliquot ages. Notably, these AHe ages are younger than the depositional age of the parent rock, the Moruga Formation (early Pliocene), indicating that the apatite has been reset to temperatures of at least 60°-90° C. Nine sandstone well-cutting samples from the Southern Basin yield single grain ZHe ages that range from early Miocene to Proterozoic and single grain AHe ages of middle Pliocene to late Cretaceous. These Southern Basin samples were collected from two formations: the Lower Cruse with a depositional age of late Miocene, and the Herrera with a depositional age of middle Miocene. While none of the Southern Basin ZHe ages were reset to temperatures of 180° C, the AHe ages from the Southern Basin show signs of partial resetting. Southern Basin ZHe and AHe data suggest units were buried to maximum depths of ~3-5 km. The Southern Range AHe data suggests that the sediments at the surface in the early Pliocene were syndepositionally buried to a maximum depth of ~3 km and subsequently exhumed starting in the Pleistocene. All of the reset thermochronology ages become progressively younger toward the south which is interpreted as a southward propagation of deformation away from the plate boundary to the South Coast Fault zone. This geologically very recent activity highlights the South Coast Fault zone as a subsidiary fault that has facilitated rapid rates of exhumation.