TECTONIC SIGNIFICANCE OF THE CARIBBEAN PLATE AS A REFERENCE FRAME SINCE XMA: THE “BACKBONE” EXPLAINED

The Cordilleran/Central American/Andean “Backbone of the Americas” has had a complex tectonic Cenozoic history, involving migrating triple junctions, changes in relative and “absolute” plate motion, subduction-accretion/erosion, arrival of seamounts/seamount chains/plateaux, oroclinal bending, strain/displacement partitioning, and terrane motion. The Caribbean “finger” moved through the NA-SA gap as the Americas moved west and CA moved east (mantle reference frame). By 100Ma, the Costa Rica subduction zone initiated to trap the Caribbean Plate between the Central American and Lesser Antillean subduction zones. Since then, the Caribbean Plate has been trapped in the hot-spot (mantle) reference frame with respect to which the Americas have moved westward with leading edge flat compressional subduction. Subduction-accretion has occurred on both eastern and western sides of the Caribbean Plate in front of linear neutral arcs, whereas the Mexican arc is patchily and widely distributed with compressional subduction erosion and is moving westward in the Caribbean reference frame. Throughout Cenozoic, the Andean margin has moved westward in the mantle frame, and subduction erosion has occurred. In NA, lengthening of San Andreas transform system, between N-ward and S-ward migrating triple junctions, has allowed progressive extension of Basin and Range, and dangerous flat subduction in Cascades and Mexico. Plate circuits give hotspot tracks on Pacific, Cocos, and Nazca Plates if the Caribbean Plate is fixed in the mantle frame. Fixing Caribbean Plate in the mantle frame allows the broad tectonic history of the “Backbone” since 100 Ma to be explained in an integrative way. This is illustrated, semi-quantitatively, by translation on a flat surface using vector triangles, and quantitatively (using the DeMets et al NUVEL1A relative motions and the Gordon and Gripp HS3 NUVEL1A motions in the hotspot reference frame) on stereographic projections to illustrate slip vectors, relative and “absolute” rotations, the evolution of triple junctions, and the nature of subduction zones. We pay tribute to the genius of Tanya Atwater whose 1970 paper on the plate tectonic evolution of western North America laid the foundations of the way in which it is possible, in some plate boundary zones, to relate relative plate motion, quantitatively, to geologic evolution.