Abstract

Mafic dikes and metamorphosed basaltic flows of Late Proterozoic to early Paleozoic age in western Vermont and northeastern New York have geochemical signatures consistent with their origin during progressive rifting of the ancient North American continent. The basalts change from being enriched in Ti and fight rare earth elements (REEs) to being depleted in Ti and light REEs from west to east across the western Appalachians. Western samples are similar to early-stage rift basalts as seen in the Main Ethiopian Rift, whereas easternmost samples are like mid-ocean ridge basalt (MORB) produced in axial parts of the Red Sea. Samples from intermediate geographic areas can be either enriched or depleted. By analogy with the East African Rift-Red Sea system, the chemical changes in basalts across the western Appalachians probably reflect a changing source from trace element-enriched mantle (ocean-island basalt asthenosphere or continental lithosphere) to depleted MORB-type asthenosphere as rifting progressed.

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