Sr and Nd isotopic compositions of 24 volcanic rocks from the Central American arc show an unusual positive trend that correlates strongly with crustal thickness. Nicaraguan lavas, situated on the thinnest crust, have MORB-like Nd, but elevated Sr isotopes and high 11 Be, implying a slab component in their genesis. Lavas from Costa Rica and Guatemala have lower values of both isotopes and are underlain by crust 30% thicker than that beneath Nicaragua. The regional isotopic variation can be ascribed to mixing between two reservoirs: a relatively uniform mantle wedge with a subducted oceanic component, and a lower crust. The correlation of chemical parameters with crustal thickness can be explained if the lower crust acts as a 'density filter'. Thus the least fractionated Nicaraguan lavas have the highest Sr and Nd isotopic ratios and are the most isotopically similar to the melted mantle wedge.-L.C.H.
|Original language||English (US)|
|Number of pages||14|
|State||Published - Jan 1 1986|
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