Origin of hybrid ferrolatite lavas from Magic Reservoir eruptive center,Snake River Plain,Idaho

The mineralogy and geochemical characteristics of intermediate composition ferrolatites and related lavas from the Magic Reservoir eruptive center (central Snake River Plain) have been investigated to evaluate the origin and petrologic significance of these hybrid lavas. The ferrolatites are chemically uniform, but contain a disequilibrium phenocryst/xenocryst assemblage derived in part from mixed rhyolitic and basaltic magmas that are closely represented by extrusive units in the area. The hybrid lavas also contain xenoliths of Archean granulites and have high ⁸⁷Sr/ ⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd ratios, all of which suggest significant magma-crust interaction. Quantitative models including magma mixing, minor crystal fractionation, and crustal contamination very closely reproduce the observed compositions of these ferrolatites; closed system fractionation and (or) simple bulk contamination models are not as successful and can be ruled out. It appears that preexisting mafic and silicic magmas from distinct sources (e.g., mantle and crust) encounter one another in crustal-level magma chambers under conditions where intimate mixing may occur despite wide differences in the physical properties of these liquids.