Tectonic Relations of North and South America

Abstract

The Pacific and Atlantic marginal belts of orogeny in Paleozoic time are believed to merge in central and southern Mexico and then as a single belt to swing eastward through Central America approximately to Jamaica and Hispaniola. Veering sharply southward from Hispaniola the belt includes the present submerged Beata Ridge and connects with the metamorphic core of the Venezuelan and Colombian Andes. The major Mesozoic belt of orogeny is believed to extend down the peninsula of Baja California, through the Sierra del Sur of Mexico to the Costa Rica-Panama Isthmus and the Colombian and Ecuadorian Andes. It is marked throughout by great granitoid batholiths. Another belt of late Jurassic and Cretaceous orogeny branches eastward in Central America from the main belt and follows through the Greater and Lesser Antilles to Trinidad and Venezuela to join the main belt in Colombia. This belt makes a tight U-shaped pattern and is believed to mark two tectogenes for the most part, both of which formed in the late Mesozoic time and probably in succession one after the other. A third tectogene from Puerto Rico around the Lesser Antilles to the Leeward Islands is active to-day and probably had a beginning in Eocene time. It lies outward from the late Mesozoic tectogenes. The available geophysical data in the form of gravity anomalies and seismic observations are related to the geological information in making the analysis of the tectogenes. The eastern Caribbean Basin is believed to be due to middle and late Tertiary subsidence, and the western Caribbean Basin is believed to be due to Cretaceous and early Tertiary subsidence. The Gulf of Mexico is postulated to have begun to subside in Permian time. From the sequence of events described for each of the basins in the Mexican-Caribbean region, as well as for the Banda Sea of the Dutch East Indies, an orogenic cycle is postulated as follows: (1) general epeirogenic uplift of a central region for a long time, and the shedding from it of large amounts of debris to partly surrounding basins; (2) compressional deformation in the partly surrounding basins to form a belt of major orogeny; and (3) subsidence of the former region of uplift, with the creation of a basin having deep water in places. The marginal areas of the new basin soon become sites of heavy sedimentation. From this tectonic setting a theory of orogenesis is devised which proposes asymmetrical convective flow in the mantle as the causative mechanism. The theory is applied to the Dutch East Indies and the Peruvian Andes as well as the mediterranean region between North America and South America.