Two phases (pink and white granite) of the Sebago batholith have been dated by the U/Pb zircon method. The age of both phases is 325 m.y. Zircon in the pink phase has been reset in intrusion of the Pleasant Mountain stock approx 114 m.y. ago. Zircon in the white phase lost lead only recently. Metamorphic isograds in the vicinity of the batholith approximately parallel its shape, and may be at least partly Hercynian in age. Cooling and uplift of the Sebago batholith appear to have followed a complicated path involving little or no uplift in the Middle Carboniferous to Middle Permian, rapid cooling from 275 to 225 m.y. ago, and a slow cooling since Middle Triassic. Different rates of cooling may be related to changes in the tectonic regime.-L.C.H.
Additional publication details
Carboniferous U-Pb age of the Sebago batholith, southwestern Maine: metamorphic and tectonic implications.