Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
On the maps below, different pieces of continental crust are shown in color. Present coastlines are shown. White areas are present day submerged continental crust. Subduction zones are shown as red lines with round knobs. The knobs are on the overriding side of the subduction zone. Other plate boundaries are shown as plain red lines. Oceanic crust is shown in blue. Recently formed oceanic crust (in the preceding 10 million years) is in a lighter shade. Pacific oceanic crust uses a darker shade than Atlantic crust.
170 million years ago, before the breakup of North America (green), South America (pink) and Africa (purple). Yucatan (yellow-green) occupies the present Gulf of Mexico. Mexico (orange) is adjacent to western North America but well northwest of its present position. The Chortis Block, making up Nicaragua and Honduras (yellow), lies on the Pacific side of Mexico. Oceanic crust is being subducted along the whole western side of the Americas. This is not yet the Pacific Plate. At this time the East Pacific Rise is far to the west. The Pacific Plate is west of the rise and another large plate, the Farallon Plate, is east of it. The Farallon Plate is being subducted beneath the Americas. The present Nazca, Cocos and Gorda Plates are remnants of the Farallon Plate.
North America separates from South America and Africa, with Yucatan temporarily attached to South America. The exact nature of the breakup around Florida is unclear and it is possible that Florida moved as well.
As North America moves west, new oceanic crust (light blue) forms in the gap.
The proto North Atlantic and Gulf of Mexico continue to widen and Yucatan begins to separate from South America.
Yucatan is now a separate plate. South America starts to rift away from Africa.
As North and South America continue to separate, the shear causes Yucatan to rotate counter clockwise.
Yucatan continues to rotate and South America continues to separate from Africa, which has disappeared from the map.
Mexico begins sliding southeast and begins to converge on South America.
Mexico and Yucatan begin to converge. Meanwhile, out in the Pacific, volcanism (gray) begins to build a volcanic plateau.
Yucatan collides with Mexico while the volcanic plateau continues to build.
The movement of the Farallon Plate eventually brings the volcanic plateau into the subduction zone. The volcanic plateau is too thick to subduct, so instead it begins overriding the subduction zone. A volcanic arc (brown) begins to build up on the leading edge of the volcanic plateau. This will eventually become the Antilles.
As the plateau jams between North and South America, the Chortis Block is broken loose and parts of northwestern South America are moved. Subduction begins on the southern side of the plateau and a volcanic arc begins to grow there as well. This will become the future Costa Rica and Panama.
Very long lived volcanic arcs sometimes undergo a process called back-arc spreading. The arch splits lengthwise and magma rising over the subduction zone generates new oceanic crust. This begins to happen off Yucatan, and the Yucatan Basin begins to form.
The future Caribbean continues to be jammed through the gap between North and South America, being deformed internally as it goes. Meanwhile, although we can't yet see it, the subduction of the Farallon Plate and the growth of the Pacific Plate along the East Pacific Rise have brought the North American and Pacific Plates close together.
Finally the subduction of the Farallon Plate and the growth of the Pacific Plate along the East Pacific Rise have brought the North American and Pacific Plates into direct contact. Since the Pacific Plate is moving northward more or less parallel to the west coast of North America, the plate boundary is not a subduction zone but a transform fault. This is the ancestral San Andreas Fault.
Around 5 million years ago a sliver of Mexico breaks loose and begins sliding up the coast, opening the Gulf of California. The convergence of North and South America create the land bridge of Panama and cut off the Pacific-Atlantic connection.
Created 18 January 2008, Last Update 11 June 2020