U-Th-Ba Elemental Fractionation during Partial Melting of Crustal Xenoliths and its Implications for U-series Disequilibria in Continental Arc Rocks

• Main Author: Brens, Raul, Jr.
• Format: Others
• Published: FIU Digital Commons 2011
• Subjects: Magma chamber processes; geochemistry; partial melting; radiogenic isotope geochemistry; U-series disequilibria; South America
• Online Access: http://digitalcommons.fiu.edu/etd/406; http://digitalcommons.fiu.edu/cgi/viewcontent.cgi?article=1458&context=etd

Understanding U-series isotopic disequilibria of partially melted crust is integral for determining the effect that crustal assimilation has on the U-series signature of magmas. In this work, U, Th and Ba (as a proxy for Ra) elemental abundances were gathered on the quenched glass in partially melted crustal xenoliths of granitic composition using microbeam techniques. The crustal xenoliths, which are found in basaltic lava, from Mirador Volcano in Chile, are old, and can be assumed to be at secular equilibrium, whereas melting occurred during eruption of Mirador in 1979. A comparison of the ratios Ba/Th and U/Th in the partial melts with those of the whole rock reveal how much fractionation has occurred during partial melting. Different ratios of U, Th and Ba compared to the whole rock substantiate fractionation via partial melting. Thus, assimilation of partial melts of crust can play a role in U-series isotopic disequilibria.