Crustal structure of the eastern Caribbean in the region of the lesser Antilles and Aves Ridge

Abstract

The results of two marine gravity, magnetic and seismic reflection surveys in the eastern Caribbean are presented, the principal structures surveyed being the Venezuela Basin, Aves Ridge, Grenada Trough and Lesser Antilles island arc. The data are presented in the form of charts of bathymetry, free air anomalies, Bouguer anomalies and total field magnetic anomalies. The Venezuela Basin is a broad, extensive basin with a sediment thickness in excess of 1.5 km. At its eastern margin it exhibits small negative free air anomalies and is in approximate isostatic equilibrium. The Aves Ridge is an elevated linear volcanic prominence parallel to the Lesser Antilles characterised by positive free air anomalies. Its typical form is of two basement ridges marking its western and eastern flanks enclosing a sediment filled trough. The western ridges are shown to be more dense and less magnetic than the main body of the Aves Ridge and may represent a series of intrusive bodies. The Aves Ridge exhibits strong magnetic-gravity correlations. It is underlain by a root attributed to depression of the Moho and lowest crustal layer and exhibits negative isostatic anomalies. The Grenada Trough is a basin of subdued topography in the south and more rugged topography in the north. It contains a sediment thickness in excess of 2 km. and is characterised by predominantly negative free air anomalies. It is underlain by an elevated Moho and exhibits predominantly negative isostatic anomalies. The Lesser Antilles lie on a narrow elevated ridge rising abruptly out of the Grenada Trough. The island arc exhibits extreme free air gravity gradients. It is underlain by a root attributed to depression of the Moho and is the site of a linear belt of positive isostatic anomalies. Possible modes of origin of the Aves Ridge are discussed.