U-Th-Pb Geochronology and Mineral Pb Systematics of Quaternary Basalt

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EAR-9909590DePaoloDevelopment will continue on a new method for determining the ages of young basaltic volcanic rocks, the most abundant lava type erupted on the earth. The research involves measurements of Pb isotopic composition combined with measurements of U/Pb and Th/Pb ratios in minerals, glass and groundmass in volcanic rocks. The research requires a special approach to measuring Pb isotope ratios. The approach had been developed with a previous grant, but we hope to improve the resolution. With this new technique it will be possible to better understand the processes by which magma is produced in the earth and transported to the surface for eruption. The work will focus on application of the technique to submarine mafic lavas, particularly those with low potassium concentrations. Low-K lava is widespread on the earth, and particularly difficult to date by other methods. Preliminary work shows that Pb isotopes in minerals of many basalts are more variable than expected. The causes and implications of these variations will befurther investigated as well. The rocks and minerals that will be measured will be collected from Hawaii, the western U.S., and Italy, and additional submarine lavas will be obtained from other sources. To help interpret the Pb isotope data, analyses of Sr and Nd isotopes will also be made.