The Thermal Evolution of the Grenville Terrane Revealed through U‐Pb and Fission‐Track Analysis of Detrital Zircon from Cambro‐Ordovician Quartz Arenites of the Potsdam and Galway Formations

Abstract

Tectonothermal studies of Precambrian terranes using detrital zircons have been the domain of U‐Pb dating techniques. Advancements in technology have made it possible to study the low‐temperature evolution of these terranes with the fission‐track (FT) dating method, and combining these two techniques provides a unique look at the thermal evolution of Precambrian terranes. Detrital zircon grains from the upper middle Cambrian to lower middle Cambrian Potsdam and Galway formations in New York State, which uncomformably overlie the Precambrian Grenville terrane, were analyzed by U‐Pb and FT dating. Approximately 90% of the U‐Pb ages fall between 950 and 1200 Ma, fully consistent with the idea that these zircons are derived almost entirely from Grenville‐age rock. Zircon FT (ZFT) ages from the same suite of samples have component populations of ∼540, ∼780, and ∼1200 Ma, with single‐grain ages as old as 2.1 Ga. The most important observations from the FT data are that there is no widespread resetting on either side of the Adirondacks, that the component populations are older than the age of deposition, and therefore that the principle population likely reflects the cooling ages of what was almost exclusively Grenville source rock. The ZFT component populations older than Grenville tectonic events (FT age > 1.6 Ga) suggest that these old grains and the zircon with old U‐Pb ages were transported from other nearby Precambrian terranes, such as the Superior and the Yavapai‐Mazatzal. These FT data show that the Potsdam and Galway formations have not undergone heating significant enough to reset fission tracks in zircon since deposition and that the heating in the source rocks at 540 Ma corresponds to cooling after the breakup of Rodinia and the rifting of the Iapetus Ocean.