A plate-kinematic framework for models of Caribbean evolution

Abstract

We define the former relative positions and motions of the plates whose motions have controlled the geological evolution of the Caribbean region. Newly determined poles of rotation defining the approximate spreading histories of the central North and the South Atlantic oceans are given. For the late Jurassic-Early Cretaceous anomaly sequence of the central North Atlantic, we have used previously published∗ definitions of fracture-zone traces and magnetic anomaly picks, redetermining the pole positions and angular rotations for various isochrons on an Evans and Sutherland interactive graphics system. For magnetic anomalies younger than the Cretaceous Quiet Period in both oceans, we (1) used Seasat altimeter data to help define fracture-zone traces, and (2) identified and used marine magnetic anomalies to determine the positions of spreading isochrons along the flowlines indicated by the fracture zones. By the finite difference method, the relative paleopositions and the relative motion history between North and South America were computed. This analysis defines the size and shape (and the rate at which the size and shape changed) of the interplate region between North and South America since the Middle Jurassic. Thus, a plate-kinematic framework is provided for the larger plates pertaining to the Caribbean region, in which can be derived more detailed scenarios for Gulf of Mexico and Caribbean evolution. North and South America diverged to approximately their present relative positions from Late Triassic? to Early Campanian (about 84 m.y. ago) time. This is the period during which the Gulf of Mexico and a Proto-Caribbean seaway were formed. Since the Campanian, only minor relative motion has occurred; from Early Campanian through to Middle Eocene times. South America diverged only another 200 km, and since the Middle Eocene, minor N-S convergence has occurred. These very minor post-Early Campanian motions have probably been accommodated by imperfect shear and compression along the Atlantic fracture zones to the east of the Lesser Antilles, and along the northern and southern borders of the Caribbean Plate. Accordingly, it is suggested that from Campanian time to the present, the relative motions between the North and South American plates have had only minor effects on the structural development of the Caribbean region. Primarily using the data of Engebretson et al.∗∗, the convergence history of Pacific plates with North America was calculated for two points near the western Caribbean. By completing finite difference solutions, the convergence history of the Pacific plates with the Caribbean and South American plates can be approximated. The direction and rate of convergence of the Pacific plates with the Americas may have controlled the style of subduction and possible microplate migration along the North American, South American and western Caribbean boundaries that define the eastern Pacific plate margin.