The Peekskill Granite pluton in southeast New York is a steep-walled, shallow intrusion in a major fault zone between Grenville rocks of the Reading Prong and Cambrian-Ordovician rocks of the Manhattan Prong. Emplacement of the pluton postdated folding during the Taconic orogeny and postdated the intrusion of the Cortlandt mafic complex. The pluton was probably emplaced during or following the development of the fault zone.
Rb/Sr whole-rock analyses show that the pluton crystallized about 371 ± 14 m.y. ago with an initial 87Sr/86Sr ratio of 0.7074 ± 0.0002. The field relationships and age determinations indicate that the northwestern part of the Manhattan Prong was affected by brittle fracture and faulting and by igneous activity during the Acadian deformation.