Caribbean arc tholeiites

Abstract

The occurrences of arc tholeiites in the two active subduction zones involving the Caribbean plate, Central America and the Lesser Antilles, are quite restricted. Volcanic rock suites exhibiting strong iron enrichment are limited to five volcanoes, all in Central America. Three of the five occur along the Nicaraguan portion of the volcanic front beneath which the arc crust is thinnest. On the other hand, volcanic rock suites with low absolute concentrations of large ion lithophile elements and light rare earth elements are largely confined to two northern islands in the Lesser Antilles, St. Kitts and St. Eustatius, and solely confined to the Nejapa‐Granada cinder cone alignments of Nicaragua in Central America. These tholeiitic characteristics, strong iron enrichment and low concentrations of certain incompatible elements, are produced by dissimilar processes. Strong iron enrichment results from extensive fractional crystallization at low pressure or with low water contents, perhaps in shallow magma bodies, whereas low absolute concentrations of specific incompatible elements are governed by relatively high degrees of source melting. The high degree of melting is made possible by a greater flux of material from the subducted plate. Crustal contamination exerts only a secondary and local control on incompatible element concentrations, at least in Central America.