THE LESSER ANTILLES ISLAND ARC

The island arc forms the eastern boundary of the Caribbean plate beneath which the Atlantic crust is subducted. The arc has probably been active since the early Cretaceous. It extends from the South American continent to the eastern termination of Puerto Rico and Virgin Island.

During the early, Eocene, a volcanic front settled upon the arc substratum. The arc can be traced from Grenada, in the south, to Anguilla, in the north. This trace constitutes the Older (or Outer) Arc.

The volcanic line ceased activity, and after a hiatus, the volcanism resumed along the Recent (or Inner) Arc. Between Grenada and Martinique the two arcs are imbricated; but to the north, they diverge, and from Martinique northwards, they are separated by a corridor about 50km wide.

Figure: Map of the Lesser Antilles depicting the cold deformation front, the surface trace of the subduction zone, and the Outer and Inner Arcs. Adapted from Bouysse and Westercamp, 1990.

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