Abstract by Lauren Franzen
Bart Kowallis, Eric Christiansen
Titanite zoning in the Oligocene Little Cottonwood granite, Wasatch Mountains, Utah
Titanite from the outer parts of the Little Cottonwood granite have oscillatory zoning in both grain cores and mantles. In contrast, grains from the pluton interior have cores with partially resorbed ilmenite within patchy overgrowths of titanite, surrounded by mantles with oscillatory zoning. These relations suggest initial crystallization of high fO2 magma with stable titanite on the margins of the pluton. Then a lower fO2 magma with ilmenite mixed into the still molten core of the chamber. The ilmenite partially dissolved in favor of titanite creating the patchy core zones. Titanite crystallization then proceeded through several phases of growth and minor dissolution, creating mantles with oscillatory zoning. Ilmenite inclusions in the cores later exsolved, probably under subsolidus conditions, into lamellae of ilmenite, Ti-rich magnetite, and rutile. Many titanite grains throughout the pluton also have narrow rims with interstitial extensions that have low REE and high F contents, likely formed as the magma became saturated with water.