STRUCTURAL GEOLOGY AND CENOZOIC DEFORMATION: WESTERN NORTHERN RANGE, TRINIDAD

The Northern Range, Trinidad, underwent deformation due to oblique collision of the Caribbean plate with northern South America, which was then followed by transform plate motion. Deformation began in the late Miocene when sedimentary protoliths were ductility deformed and metamorphosed to greenschist facies; this collision and subsequent transform deformation drove exhumation of these rocks to the surface and created the high topography (~1000 m) of the Northern Range. This project provides constraints on the structural history of the western Northern Range where bedrock mapping and structural analyses are most complete. Initial geologic mapping of Northern Range attempted to establish and map a protolith stratigraphy. Our approach was to simply map the observed metamorphic rock types. We supplement our new map with abundant mesoscopic structural fabric measurements collected from roadcut, streambed, and quarry exposures. We synthesized the new map and all structural data into a GIS geodatabase. The data were used to construct cross-sections and stereonets along a continuous N-S transect across the entire western Northern Range. Our analyses highlight three major phases of deformation in the western Northern Range. D₁ (early Miocene) produced a S₁ foliation that completely transposed the original stratigraphy and dips south at an azimuth between 150–220°. D₂ folded S₁ into asymmetric trains of south-verging m- to dm-scale mesoscopic folds, yet the timing of D₂ is not well constrained. D₃ produced conjugate sets of NE-SW- and NW-SE-trending f₃ folds. D₃ is probably associated with Pliocene extension related to the local development of pull-apart basins. The cross-sections and detailed analyses also traverse important southern range-front structures, including: 1) range-front domains of upright NW-SE trending folds, and 2) the range-bounding Arima Fault zone. We characterize the Arima Fault as an ~100m wide zone of inactive (Plio-Pleistocene?), ~E-W trending, sub-vertical (both N- and S-dipping), predominantly normal sense, fault zone.