Basalts thorium/lead isotopic

O Hara MJ (1968) The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks. Earth Sci Rev 4 69-133 O Nions RK, McKenzie D (1993) Estimates of mantle thorium/uranium ratios from Th, U and Pb isotope abundances in basaltic melts. Phil Trans Royal Soc 342 65-77 Oversby V, Gast PW (1968) Lead isotope compositions and uranium decay series disequilibrium in reeent volcanic rocks. Earth Planet Sci Lett 5 199-206... 

Altliough plagioclase, unlike calcium-rich pyroxene, ilmenite, or zircon, does not readily incorporate uranium or thorium, isotopic compositions of lead in plagioclase are of particular interest. Plagioclase is a dominant mineral phase in the lunar crust and a major constituent of mare basalts that can incorporate lead into cation sites normally occupied by potassium, sodium, or calcium and thereby play an important role in the U-Th-Pb isotopic systematics. 

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