The inference of a volcanic sea-floor–spreading genesis for the lithospheric slab beneath the Caribbean Sea is supported by the discovery and mapping of large easterly trending lineations of crustal magnetism within the Colombia basin. Furthermore, critical examination of available descriptive data and theoretical calculations strongly imply that the Colombia basin linear magnetic anomalies are not associated with sediment-buried topography of the Colombia basin igneous crust.

The direction of decreasing crustal ages within the Colombia basin can be utilized as a first-order test of plate-tectonic genetic syntheses of the Caribbean Sea floor. The easterly trending anomalies of crustal magnetism and the smooth floor of the basin imply that the parent spreading center lay either to the north or to the south of the present physiographic boundaries of the basin.

The direction of decreasing crustal ages within the Colombia basin cannot be conclusively deduced from available data. The igneous crust beneath the basin floor has not yet been directly sampled. However, a correlation of the Colombia basin crustal magnetic anomalies with Late Cretaceous index anomalies 27 to 33 can be made if the assumption of a nearly constant rate of crustal genesis is valid. This crustal magnetism age correlation implies that the parent spreading center lay to the south of the basin. The correlation is inconsistent with a simple Pacific-emplacement theory and suggests that the Isthmus of Panama did not evolve upon the Colombia basin lithospheric slab.

Direct crustal sampling in the Colombia basin by the next Deep Sea Drilling Project expedition to the Caribbean Sea (projected date, July 1975) is suggested as a meaningful test of the basin's sea-floor spreading genesis. If crustal ages can be established through drilling to the igneous basement, then the mapped distribution of linear magnetic anomalies could be sufficient to firmly establish the age gradient of the lithospheric slab beneath the central Caribbean Sea.

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