A Terrain Corrected, Bouguer Anomaly Map of Central Trinidad: Looking for a Crustal Root beneath the Neotectonic Central Range Fault Zone

The Central Range on the island of Trinidad is a locus of active mountain building. The island straddles a transpression collision between the Caribbean and South American tectonic plates. GPS studies show the Caribbean plate moving 20 mm/yr eastward relative to a fixed South American plate. These data show that Central Range fault zone is the most active part of the plate boundary accommodating approximately 12 mm/yr of that motion. A crustal root is expected to form below this emerging mountain range because the added topographic mass of the range requires additional isostatic support. The size and shape of the Central Range crustal root may provide information about the magnitude of the on-going collision. To characterize the crustal root, 2806 gravity measurements from the National Geospatial-Intelligence Agency database were analyzed. The development of a crustal root displaces the dense mantle away from the surface of the Earth and creates a gravity low. The shape and magnitude of this low provides information about the size and shape of the crustal root. Standard drift, earth tides, latitude, free air, and Bouguer corrections were applied to the data. A 30 meter digital elevation model (DEM) was used to calculate the terrain correction. We present a terrain corrected, Bouguer anomaly map of central Trinidad. The data show a clear increase in the gravity from south to north across the island. This gradient documents the transition from continental crust to the south (South America) to oceanic crust to the north (Caribbean). Removal of this gravity gradient should isolate the signal of any crustal root beneath the Central Range. If present, the size and extent of the crustal root can be modeled using standard forward modeling techniques.