The petrogenesis of basaltic and andesitic magma at continental convergent margins will be investigated using the Andean Central Southern Volcanic Zone, Chile, as a natural laboratory. Problems to be addressed are: 1) How are diverse basaltic magma generated concurrently from the sub-arc mantle wedge and 2) How is andesitic magma generated from basaltic magma in a continental arc setting A hypothesis, based on previous work, that large basaltic stratovolcanoes are generated by flux melting of the mantle wedge, whereas small eruptive centers (SEC) are decompression melts of "aged" subduction-modified mantle wedge, will be tested. Basaltic rocks will be analyzed for fluid-mobile elements (B, Sb, Mo, Sn), and U-series isotopes (230Th, 226Ra, 238U, 232Th). Melt inclusions in olivines will be analyzed for volatile elements (H2O, CO2, Cl, S, F). These results will help to determine the wedge composition during melting, and the timing of melting and ascent of basaltic magma. Andesites from two volcanic centers, exhibiting contrasting bulk rock trends of low-pressure fractional crystallization of degassed magma and crustal assimilation and hornblende crystallization, will be examined through analysis of minerals, groundmass and melt inclusions using electron microprobe, ion-microprobe and laser ablation ICPMS. U-series isotopes will be studied in selected basalt-andesite pairs to compare the timing of distinct differentiation processes. Results will contribute to an understanding of magma generation in continental arcs, and to fundamental geologic/geochemical issues such as the processes and time scales for mass transfer of subducted materials to the mantle wedge and to the continental crust. An internet-based database of petrographic and chemical data for the collection of SVZ rock samples housed at FIU will be developed as part of this project, and research will integrate FIU undergraduates participating in an ongoing NSF-funded project to enhance diversity in the geosciences. The PI and students will attend the 2004 IAVCEI General Assembly in Pucon, Chile, and further research interactions with Chilean colleagues.
