Chapter 15 Tectonic evolution of the grenada basin

Abstract

Detailed analyses of gravity, seismic reflection and refraction data are integrated with an earlier interpretation of magnetic data to produce a coherent model for the tectonic evolution of the Grenada basin that suggests that the basin formed by near east-west extension. Although the seafloor of the Grenada basin changes from smooth and undisturbed in the south to rugged with relatively high relief in the north, Bouguer anomalies and two-dimensional and three-dimensional gravity models, based upon seismic refraction and reflection data, reveal that the crust gradually thins in an east-west sense towards the center of the basin. Typical back-arc crust is observed in the southern part of the basin, but refraction data are not sufficiently reliable in the northern part to adequately determine the nature of the crust. Several curvilinear discontinuities in magnetic, gravity and bathymetric trends are observed. These discontinuities, when integrated with two-dimensional and three-dimensional modeling and analyses of Bouguer gravity anomalies, are interpreted to be due to late Tertiary compressional forces in the northern part of the region. These compressional forces have resulted in the bifurcation of the Lesser Antilles island arc north of 15∘N, the westward displacement of part of the Aves Ridge (a remnant island arc), and the crustal deformation observed in the northern Grenada basin. The compressional forces also appear to have sufficiently disrupted the crust in the northern Grenada basin such that earlier magnetic anomaly patterns have been modified to yield the observed magnetic signature.