Speed, R., and C. Bina, Alkalic magmas of the southern Lesser Antilles arc related to arc-continent collisions, Eos, Transactions of the American Geophysical Union, 67, 1278, 1986.
The Neogene Lesser Antilles arc lies above the leading edge of terranes that override the South and(?) North American plates. Magmas in the southern Lesser Antilles (SLA=Grenada. Grenadines) are anomalously alkalic, increasingly so from Miocene to present, relative to calcalkaline magmas to the north. From tectonic studies, we claim the SLA have progressively encroached on and overridden the passive margin of the Precambrian South American continent in Neogene time. Thus, the alkalic magmas are probably due to the existence of old sialic crust and/or fringing terrigenous sediments below the SLA.
Isotopic data (Sr, Nd, Pb, O) for volcanic rocks of the Neogene SLA permit two models of evolutions of the alkalic magmas by mixing of two fluid components: 1) fluids/melts from downgoing oceanic crust interact with the overlying mantle wedge to give one component and melts or fluids in suprajacent (unrecognized) continental crust in the arc, the other; and 2) fluids melts from a downgoing continental crust and/or sediment wedge form one component and partial melts derived from the overlying mantle wedge and/or primitive arc crust the other component. The occurrence of Neogene collision between the SLA and continental South America and the seismic structure of SLA support the second model.Copyright © 1986 American Geophysical Union