This project is to investigate the origins and tectonic significance of intermediate composition flood eruptives that re associated with continental rifts. Chemical and radiometric isotopic analyses of approximately 10 natural flood phonolite and trachyte lavas will be used to constrain possible source reservoir(s) and the evolution of these lavas. Melting experiments on samples from this suite will be used to examine the processes and the P, T. and composition conditions necessary for the genesis of these lavas. Possible source mineralogies, polybaric and polythermal crystallization sequences, and the role of volatiles in partial melting and mass transport will be identified. Complementary studies of compositionally simplified analog systems will facilitate interpretation of phase relations and extrapolation of results to different magma compositions. Forward approach studies, if appropriate, will test petrogenetic models that result from the inverse experiments. The result of this integrated experimental and analytical approach are relevant to understanding heat and mass transfer from mantle to crust during rifting, identifying the involvement of crust in rift magmatism, and developing geophysical models for rift evolution and structure.
