Haïti devient-il un lieu maudit par les séismes ?

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Haiti, formed on a lump of Gondwana!

Is Haiti becoming a place cursed by earthquakes?

Through modern chemical analyses, researchers at the University of Florida have discovered that very ancient rocks are present under the island of Hispaniola. The kind of debris left by the supercontinent Gondwana, they will be transported for nearly 1,500 km, through the tectonic movements of the Caribbean plate.

 Geologists have so far believed that Hispaniola, the island home to the Dominican Republic and Haiti, was geologically relatively young. About 150 million years ago. But analyses by researchers at the University of Florida have reversed that perspective. The chemical composition of rocks helps us to know their origin. Detailed studies of rare element concentrations such as strontium or neodymium and isotopic ratios of elements such as lead provided researchers with a kind of rock identification label. They can thus discover the source of the lava or magma from which they come, and reconstruct the tectonic displacements caused by the terrain they have formed.

A double surprise

 Professor Michael Perfit's team examined the lava that quickly turned out to have been spat out during an eruption 1 million years ago. First surprise, because the last known volcano on the island dates back 40 million years. But the main discovery is yet to come. After analyzing the plasma source mass spectrometer (ICPMS), geochemists found oddities in the composition of the samples. Throughout the rest of the island and more widely throughout the Caribbean arc, there are subduction zone lavas: basaltic oceanic crust, ancient and dense, subducting under another lithosphere, oceanic or continental, resulting in deformation and volcanic formation. Here, however, the curves show very different concentrations of trace elements. They are strikingly similar to what one might encounter in the case of volcanoes occurring in the center of a continent. And the rocks of the superposition, the source of this lava, seem to be at least 1 billion years old. 

An incredible journey 

 To solve the puzzle, he must take a solution more than 1,500 km away. At the level of Central and South America, there are rocks of this type. This is Terranes Grenvillian, fragments of ancient continents testify to distant ages in the history of the planet or emerging lands without the same terms.

Ainsi, il semble qu'Hispaniola soit, au moins en partie, située sur les restes d'une croûte continentale très ancienne qui faisait partie intégrante du supercontinent Gondwana qui existait il y a des centaines de millions d'années. Au moment de son éclatement en plusieurs blocs, dont l'Amérique du Sud et l'Afrique, suivi de l'expansion orientale de la plaque des Caraïbes, une partie de cette ancienne lithosphère continentale avait été emportée. Transporté dans sa coque supérieure comme un rondin dérivant entre deux plans d'eau, il aurait survécu sinon dissipé lors de son périple de plus de 1 500 km jusqu'à son emplacement actuel. Les géologues pensent que ce type de débris formerait une sorte de noyau autour d'îles, voire de continents, qui pourraient se former et grossir.

Par Jean-Emmanuel Rattinacannou, Futura

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