COMPARISON OF MAGMA SOURCES IN THE MODERN CARIBBEAN VOLCANIC ARC TO SEDIMENT ENRICHMENT SOURCES IN THE CENTRAL AMERICAN ARC

Considerable effort has been put into deciphering the relationships between mantle, crustal and sedimentary inputs into arc volcanic systems. Volcanic arc lavas incorporate a package of elements from sedimentary materials in the down-going slab. In some arcs at least one other component seems necessary to explain high Ba/La ratios. Central America has the highest Ba/La found (100 to 135) along with high Ba (up to 1610 ppm), B and δ¹¹B. Combined, this is thought to be produced by subducting sediments. Lavas from other arcs exhibit moderate Ba/La and B signals, but are enriched in LREE and LILE, a signal also thought to be inherited from sediment subduction. Past work suggests that the southern Caribbean arc has a subducted sediment signature derived from Orinoco and or Amazon river sediments, as evidenced by high La/Sm (3.5 - 6), low Nb/Y (< 0.5), high B (up to ~50 ppm), along with moderate to high Ba and Sr in melt inclusions. In contrast, only oceanic sediments subduct in the northern Caribbean arc, and should show different chemical signatures from lavas of the south. The Lesser Antilles have generally been studied as individual islands, comprehensive studies of along arc variations of trace and fluid mobile elements has yet to be completed. This study begins to examine these relationships through the analysis of a comprehensive suite of volcanic rocks from Lesser Antilles.

We present preliminary trace and FME results along the Caribbean arc. The southern Caribbean does not show significant Ba/La enrichment (Ba/La = 12 - 47) suggesting that Central America is unique among arcs in this respect. However trace element and REE suggest Grenada is chemically similar to the subducted sediment from ODP Site 144 while Martinique is more similar to that of ODP site 543. Our data point to the modification of Antilles mantle sources by fluid addition or partial melting of sediment in both the southern and central parts of the arc. We find that the thicker and chemically distinct sediments in the south have no more influence on the Grenadian rock composition than the thinner package delivered to Martinique. Trace element ratios and REE patterns are a likely result of different degrees of partial melting with contributions from the sediment package the degree to which varies even among samples from the same island.