Tectonic Evolution of the Late Cretaceous-Cenozoic Lesser Antilles Subduction System and the Mesozoic-Recent Rifted-Passive Margin of Northern Morocco Using an Integration of Geologic, Seismic Reflection, and Gravity Data

The largely submarine, 850-km-long, late Cretaceous to recent Lesser Antilles subduction system consists of the Aves Ridge remnant arc, the Grenada back-arc basin, the Lesser Antilles volcanic arc (LAVA), the Tobago forearc basin, and the Barbados accretionary prism. Differing tectonic models have been proposed to explain the origin of these five main components of the Lesser Antilles magmatic terranes and their intervening sedimentary basins. Chapter 2 of this thesis tests three of these differing tectonic models using three dip-direction and one strike-direction gravity transect. Based on the integration of the crustal thickness information from the gravity transects and a compilation of radiometric dates, the tectonic model that best fits the gravity profiles and dates include: 1) an eastward shift about 190 km of the volcanic arc from the late Cretaceous Aves Ridge to its present-day location of the LAVA during the Oligocene; this eastward shift was likely a response to slab rollback; and 2) a westward shift of 180 km from the inactive Outer Arc to the presently active Inner Arc (13-5 Ma); this westward shift was likely a response to the subduction of elevated areas of fracture zones in the Atlantic oceanic. Chapter 3 of this thesis describes the 950-km-long, Jurassic Agadir-Essaouira-Rharb marginal rift underlies the Mesozoic-Recent, rifted-passive margin of northwestern Morocco. Seismic data integrated with gravity models show that the 8-15 km-thick necked zone of rifted continental crust is overlain by a single marginal rift that concentrates the thickest (1-5 km) area of Jurassic salt. The four 170-280-km-long, dip 2D gravity models created along the coast of northern Morocco were constrained by several previous refraction studies and delineate three crustal provinces of the rifted-passive margin: 1) early Jurassic oceanic crust of the deepwater area of the Atlantic Ocean; 2) thinned continental crust that includes the marginal rift on the slope and outer shelf; and 3) full-thickness and unstretched continental crust of the shelf and land areas of Morocco. The integration of the gravity models with the seismic reflection data helped constrain the width and depth of the marginal rift, which was not well imaged from seismic reflection data.