Lead isotopic fingerprinting of tectono-stratigraphic terranes, east-central Alaska

Abstract

Common lead isotopic compositions have been determined on feldspars from meta-igneous rocks from nine tectono-stratigraphic terranes or subterranes in east-central Alaska. Most of the terranes have distinct and well-defined signatures in terms of isotopic composition; thus, most can be distinguished on conventional lead isotopic diagrams. Lead isotopic ratios provide evidence for (1) possible sources for the igneous rocks, (2) time of metamorphism, (3) correlation of terrane fragments, and (4) delineation of juxtaposed terranes. Determination of lead isotopic ratios from igneous rocks can be useful in characterizing tectono-stratigraphic terranes (as to mantle or crustal origin) and in correlation, particularly where terrane relationships are enigmatic.