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Neogene Tectonic Phases of Central and Southern Trinidad Based on Brittle Tectonic Analysis of Faults Exposed in Coastal Cliffs and Rock Quarries

Paul Mann1, Jean-Claude Hippolyte2, and John Weber3
1 Jackson School of Geosciences, The University of Texas at Austin, Austin, TX
2 University of Savoie, Le Bourget de Lac, France
3 Department of Geology, Grand Valley State University, Allendale

Most previous structural studies of Trinidad have focused on its older pre-Cenozoic rocks exposed in the Northern Range with far fewer systematic structural studies of the widespread folded and faulted rocks of Neogene age. We applied methods of brittle tectonic analysis to 31 fresh exposures of striated, mesoscopic fault planes mainly located along coastal cliffs and in rock quarries. We identified three phases of deformation: 1) Phase 1: post-middle Miocene to pre-Pliocene, ENE shortening. The shortening axis is enigmatic because it parallels the present-day ENE trend of axial traces of folds on the island; we suspect this older event may reflect CCW block rotations; 2) Phase 2: Pliocene SSE shortening. This phase is orthogonal to and likely responsible for the ENE-trending foldbelt of central and southern Trinidad; because this shortening direction is almost at right angles to the ENE-striking, right-lateral Central Range fault zone, this phase may have preceded the onset of strike-slip motion along this major fault. Fold effects on the SE coastal exposures dominate over the NS-trending growth normal faults proposed by previous workers. Normal faults in coastal exposures trend ENE, parallel fold axes, and record gravitational slumping off of anticlinal highs. Phase 3: Plio-Pleistocene SE shortening. This phase likely accompanies right-lateral strike-slip motion along the ENE-striking Central Range fault zone, which is currently active and may accommodate up to 80% of present-day Caribbean-South American plate motion known from previous GPS studies.