Age of Skarn Formation and Meteoric Water Infiltration in the Willsboro–Lewis Wollastonite District (Adirondack Highlands, New York).

The article focuses on the geochronology and oxygen isotope systematics of the Willsboro–Lewis wollastonite skarn district at the margin of the 1.15-billion-year-old (Ga) Marcy anorthosite massif in the Adirondack Highlands, New York. It presents evidence that skarn formation, anorthosite emplacement, and infiltration by heated meteoric water occurred contemporaneously around 1150–1140 Ma during the Shawinigan orogeny, with subsequent metamorphic overprinting during the Ottawan (1.09–1.02 Ga) and Rigolet (1.01–0.98 Ga) phases of the Grenville orogeny. Zircon U–Pb dating and oxygen isotope analyses reveal preservation of igneous zircon cores with low δ^18O values indicative of meteoric water interaction during skarn formation, as well as metamorphic zircon growth in equilibrium with host minerals during later tectonothermal events. The study supports a model of shallow crustal emplacement of the Marcy anorthosite massif during crustal thinning following the Shawinigan orogeny, with the Marcy massif acting as the heat source driving a large meteoric hydrothermal system responsible for the extensive wollastonite skarns.