The island of Hispaniola – home to Haiti and the Dominican Republic – is generally considered to be relatively young, geologically, with rocks no older than about 160 million years. But a team of geologists led by George D Kamenov of the University of Florida has found lavas on the island that suggest that the local area is underlain by rocks that are almost a billion years older than this.

The lavas were the result of volcanic activity that probably occurred less than one million years ago in the region of the fault system that caused the earthquake in Haiti in January last year. The existence of this volcanic activity is unexpected as it postdates the previously known active volcanism in this part of the Caribbean by at least 40 million years.

Chemical analysis of the lava showed that it was probably derived from billion-year-old rocks that are today found in Central and South America, at least 1,600 kilometres away. These fragments of the Earth’s crust are thought to be surviving portions of the supercontinent of Gondwana.

In a paper published in Nature Geoscience, the scientists suggest that a piece of crust was captured by the Caribbean tectonic plate as it moved between North and South America. This fragment then migrated eastwards across the upper mantle to its current position in Hispaniola. If one of the faults found in the area was deep enough, it may then have acted as a conduit for magma to reach the surface, bringing the crustal remains up to their present position.

September 2011