The petrogenetic significance of interstratified high- and low-ti basalts in central Nicaragua

Basalts erupted from recent volcanoes in central Nicaragua can be divided into distinct high-and low-Ti suites. Low-Ti basalts have higher concentrations of LILE and LREE than high-Ti basalts. In addition, low-Ti basalts have obviously higher Ba/La, La/Sm, and ⁸⁷Sr/⁸⁶Sr, and lower Ti/Zr, than high-Ti basalts. In contrast, there are no mineralogical or petrographic differences between the two suites.The differences between the high-and low-Ti basalts of central Nicaragua are inherited from their source regions. The primary magmas of both are generated in the mantle wedge. However, low-Ti primary magmas come from parts of the wedge which bear a strong subduction zone signature, including that of subducted pelagic sediment. On the other hand, the primary magmas of the high-Ti basalts are generated in parts of the wedge relatively free of subduction zone influence.Subducted pelagic sediment can therefore be a key source component at active continental margins as well as at island arcs. Pelagic sediment could also be responsible for subtle high-field-strength element fractionations within subduction zone magmas. The mantle wedge beneath Nicaragua, which is variably modified by the subducting plate, is relatively enriched suboceanic mantle.