THE NW MARGIN OF SOUTH AMERICA IN JURASSIC TIME: SOUTHERN EFFECTS OF THE OPENING OF THE GULF OF MEXICO AND PROTO-CARIBBEAN TECTONICS

The northernmost record of Jurassic rocks includes, from west to east, the Santa Marta massif, Perija Range - Cosinas Range, Merida Andes – Santander massif, and in the subsurface two grabens: Maracaibo and Espino-Arauquita. Paleomagnetic data in the Santa Marta massif indicate a southern paleolatitudinal position in Middle Jurassic time and northern equatorial position in Aptian time. In contrast, paleomagnetic data in the Perija-Cosinas and Merida Andes indicate that Jurassic and Lower Cretaceous strata accumulated in northern paleo-latitudes, with slightly higher latitudes in middle Jurassic time and equatorial latitudes in Early Cretaceous time. After restoration of the Cosinas-Perija ranges, due to 40 to 90º of clockwise rotation, all the ranges and subsurface basins shows a fan-like geometry of an extensional system, with a north-striking Perija-Cosinas system, changing gradually to northeast-striking in the Merida Andes and more eastward for the Espino-Arauquita graben system in the subsurface.

Depositional systems in those ranges are very similar, with dominance of red volcaniclastic strata, epiclastic deposits and volcanic rocks, and localized presence of magmatic centers. Stratigraphic thickness may reach 7-9 kms in some areas, and abrupt changes in thickness occur across normal faults. All of these deposits accumulated in an extensional regime, with rift-axis trend changing from N-S to ENE, and all the systems ending toward the Santander massif. The restored configuration of the Lower-Middle Jurassic subduction zone in the pacific margin also changes in strike at the latitude of the Santander massif. The Jurassic extensional basins and associated magmatic arcs in the northernmost South America plate and amalgamated Mexican terranes were more dispersed, in contrast to the linear trend a subduction magmatic arc father south. The development of the proto-Caribbean plate that separated Mexican and Colombian terranes, and the influence of the opening of the Gulf of Mexico, favored the formation of extensional basins along the NW corner of South America.